Nutlet morphology and micromorphology of 27 species with four varieties of Carex sect. Paniceae were observed under scanning electron microscopy（SEM）. The results showed that：（1）The nutlet shape of all samples（beak excluded） were obovoid trigonous， with the length ranged from 1.53-3.59 mm. The nutlet length between different populations of the same species revealed stability and no significant difference exist by statistical analysis. （2）The epidermal cells were five to seven gonal， rarely four or eight， which was various within the different individuals of C. rouyana. The anticlinal wall was straight or microwave， and silica platform was flat， occasionally concave or slightly convex， with solitary central silica body but without satellite body. Whereas each epidermal cell of C. filipes var. kuzakaiensis and C. filipes var. tremula occasionally had two central silica bodies. （3）Based on the shape of epidermal cells， numbers of central silica platform， some species were distinguished from similar species， such as C. baimaensis and C. filipes， and it was also valuable to distinguish the varieties of C. filipes， ie. var. kuzakaiensis， var. oligostachys and var. tremula. （4）Sections Paniceae s.s. and Laxiflorae had a high consistency in the morphology and micromorphology of nutlets. It indicated that the morphology and micromorphology of nutlets were of great importance of taxonomic significance.
In order to explore the karyotype characteristics and evolutionary relationship of different populations of Sophora alopecuroides， the karyotype characteristics and evolutionary of six natural geographic populations distributed in Inner Mongolia， Gansu， Ningxia were analyzed respectively， and chromosome conventional slicing technology was used. The results showed that the number of chromosomes in six populations of S. alopecuroides was constant，2n=2x=36. There were two types of central centromere（m） chromosome and sub-central centromere（sm） chromosome in three populations. Chromosomes of most populations were only central centromere chromosome except for Population 3 in Wuwei， Gansu， with central centromere and sub-central centromere chromosome. The average arm ratio of chromosomes ranged from 1.19 to 1.37， the length ratio was between 1.72 and 2.19， and the karyotype asymmetry coefficient was from 54.30% to 57.17%. There were three types of karyotypes including 1A， 3A and 2B for S. alopecuroides. The karyotype asymmetry coefficient of population 3 of S. alopecuroides was the largest and the evolutionary degree was the highest， while those of population 19（Ordos， Inner Mongolia） was the smallest and the lowest. Cluster analysis showed that the six populations of S. alopecuroides were aggregated into two major branches of A and B. Branch A could be divided into two subclades of C and D. Among them， population 5（Wuwei， Gansu） and population 13（Alxa， Inner Mongolia） were clustered into subclade C， which had the closest relationship， whereas population 3 was clustered into subclade D alone， which was relatively distant with two populations from subclade C. Similarly， branch B could be further divided into subclade E and subclade F respectively. Subclade E was consisted of population 19 and population 43（Ordos， Inner Mongolia）， which had the closer relationship， while Subclade F only contained population 17（Yinchuan， Ningxia）， which had the relatively distant with two populations from subclade E. In this study， the chromosome number， karyotype characteristics and evolutionary trend of S. alopecuroides were discussed at the population level， which provided cytological evidence for further studying the system and evolution， and genetic diversity of germplasm resources of S. alopecuroides.
The perennial fern Pteris vittata（Pteridaceae） is a hyperaccumulator of arsenic and is used for remediation of soils contaminated by heavy metals. In order to identify the characters that the P.vittata sporophyte thrives in xeromorphic rocky environments and hyperaccumulates ions， the brightfield and epifluorescence microscopy were used to investigate the anatomical structures and histochemical features of this species. The results were as follows： （1）The structure of the rhizome， adventitious roots and leaves of P. vittata sporophytes were all primary structures， the adventitious roots had an vascular bundles， endodermis with Casparian band， lignified sclerenchyma layers， cortex， rhizodermis. （2）The rhizomes had a dictyostele， endodermis， cortex， epidermis， cuticle. （3）The stipes had a single vascular bundle with a central endodermis， cortex， sclerenchyma layers， while the epidermis had a cuticle. The pinnae had bifacial mesophyll with palisade tissue and spongy tissue， the epidermis had a cuticle. （4）The surfaces of the rhizodermis and the root hairs were pectin-rich and underlain by a lignified cortex， and permeability tests using a berberine tracer showed that these structures retained large volumes of berberine. In summary， the suberized endodermis， lignified sclerenchyma layers， bifacial mesophyll， and a cuticle， all of which reflect an adaption to xeromorphic rocky environments. The result of the berberine permeability test are consistent with the hyperaccumulation of ions by P. vittata.
To clarify the function of SPL gene in growth and development of Betula platyphylla，the BpSPL9 gene was cloned， and the expression vector of BpSPL9 was constructed by CREST technology， and the genetic transformation was carried out by Agrobacterium mediated method， and the phenotype of the transgenic lines was observed， respectively. The results showed that the transgenic lines with BpSPL9 suppressed were successfully obtained. The height of transgenic lines was significantly lower than that of non-transgenic lines， with shorter node spacing and smaller leaf area. The contents of 6-BA and IAA in transgenic lines were lower than those of the non-transgenic lines. It is speculated that BpSPL9 gene participated in plant growth and development by affecting the synthesis of auxin and cell division.
In order to reveal the mechanism of Ricinus communis response to heavy metal cadmium（Cd） stress， and screen out the resistance genes involved in Cd stress， by observing the seed germination and plant growth status， castor plants treated with water were used as controls to study their effects under three doses（300， 700 and 1 000 mg·L-1） of Cd stress. The response mechanism is expected to provide new ideas for revealing the defense and detoxification mechanism of castor plant under in Cd stress. Using differential proteomics to analyze the network regulation mechanism of castor under Cd stress， that is， with the increase of Cd stress concentration， the castor plant blocks the absorption of heavy metal Cd by roots， improves their own antioxidant capacity， and inhibits Cd2+ operation. As well as the induction of programmed cell death and other detoxification processes to resist Cd stress damage； according to the results of omics analysis， a significantly different gene RcBSK7 was screened. Through functional verification in Arabidopsis， it can be seen that this gene can improve tolerance of castor plants to Cd stress. This study enhances the understanding of the diversity and complexity of castor plants under three Cd stresses， and provides a valuable theoretical basis for the identification of Cd-tolerant genes and the restoration of heavy metal pollution in the soil.
To clarify the genetic diversity and genetic structure of a rare and the endangered small population of Ferula fukanensis， it is the basis and prerequisite to develop effective conservation and management strategies. The genetic diversity and structure of 87 endangered plants F. fukanensis from three populations based on 10 pairs of SSR primers with good polymorphism and stable amplification were analyzed respectively. The results showed that small population of F. fukanensis had relatively high genetic diversity， the Nei’s gene diversity index（hS） among the populations was 0.514， the total Nei’s gene diversity index（hT） was 0.516， the observed heterozygosity（Ho） was 0.881， the expected heterozygosity（He） was 0.512， the Shannon information index（I） was 0.836 and the percentage of polymorphic bands（PPB） was 100%， and the genetic differentiation degree of F. fukanensis was very low（Fst=0.007）， 95.9 % of the variation of F. fukanensis occurred within populations， and there was no significant correlation between genetic distance and geographical distance， 66.7% of the populations suffered from genetic bottlenecks. The results showed that F. fukanensis had abundant genetic variation and high evolutionary potential. Based on the current situation of this wild population， it is suggested to establish a protected area， and carry out in situ conservation and strengthen ex situ conservation measures such as introduction and artificial breeding to assist the conservation of F. fukanensis. This study can provide theoretical support for the conservation of plant resources of F. fukanensis and has important theoretical and practical significance.
Flavonols play important roles in plant responses to various environmental stresses and in the regulation of seed coat development. In this study， a transparent seed coat mutant was obtained through ethyl methane sulfonate（EMS） mutagenesis screening， compared with wild-type Arabidopsis thaliana（Col-0）， the mature seed color of the mutant was yellow， and its phenotypic trait was controlled by a recessive single gene. Using map-based cloning and fine-mapping technology， the mutant gene TT4（At5G13930） was mapped to BAC of MAH20 on chromosome 5， and the 1 299th base C of the TT4 was mutated to T， resulting in the 324th amino acid glycine mutated to glutamic acid. TT4（transparent testa 4） encoded a structural gene for flavonoid synthesis， chalcone synthase（CHS）， and after mutation， the seed coat was transparent and the seed color was yellow， then the mutant was named tt4-1. The phenotype of brown seed coat was restored by functional complement mutants， which further demonstrated the important role of TT4 in regulating the development of seed coat color. The tissue expression analysis of TT4 was conducted by promoter coupling GUS assay， and it was found that TT4 gene was expressed in the roots， stems， leaves of plant seedlings and flowers respectively. Physiological phenotypic analysis showed that the mutant tt4-1 seeds germinated earlier， and the seedlings had shorter taproots， as well as more lateral roots and root hairs， larger stomatal opening and higher water loss rate in mature leaves compared with the wild type. This study would lay a theoretical basis for further elaborating the function of TT4 gene.
In order to elucidate the mechanism of tapping panel dryness（TPD） and effectively control it， the ultrastructure and the expression patterns of reactive oxygen species（ROS）-related genes in barks from healthy（H） and different degrees of TPD trees were studied in this study. The results showed that with the development of TPD， aberrant mitochondrial ultrastructure changed including the loss of the matrix， swelling of cristae， and the cavitation of the inner cavity were observed in barks. The results of qRT-PCR experiments showed that the expression levels of HbPOD2 and HbPOD3 in TPD trees were higher than those in healthy trees， indicating the possibility of these genes being used as “marker” genes to monitor the tapping intensity， the stimulation intensity， and the occurrence of TPD. The gene HbCAT was also down-regulated in TPD trees， indicating that the balance between ROS generation and scavenging may be a key factor in the occurrence of TPD in rubber tree. The expressions of HbGST1， HbGST2， and HbPPO in TPD trees were higher than those in healthy trees， indicating these genes may be associated with in-situ coagulation of latex during TPD occurrence. This study reveals the changes of ultrastructure and the expression patterns of ROS-related genes in rubber tree barks during TPD occurrence. These findings may provide a new perspective for elucidating the mechanism of TPD in rubber tree， and provid theoretical guidance for developing methods for monitoring tapping intensity and stimulation intensity and for developing TPD-related “marker” genes in rubber trees.
In order to explore the regulatory effect of exogenous hydrogen sulfide（H2S） on the levels of organic acids and hormones in plants under saline-alkali stress， naked oats（Avena nuda） were used as materials to study the effect of spraying 50 μmol·L-1 H2S donor sodium hydrosulfide（NaHS） solution on the contents of organic acids and hormones in leaves and yield traits under 3.00 g·kg-1 saline-alkali stress. The results showed that saline-alkali stress significantly increased the contents of succinic acid， butenedioic acid， malic acid， glucuronic acid and total organic acids， respectively， but significantly decreased the contents of pyroglutamic acid， jasmonoyl-isoleucine（JA-Ile）， trans-zeatin（tZ） and N6-（Δ2-Isopentenyl） adenine（iP） in leaves respectively. Under saline-alkali stress， spraying NaHS solution significantly increased the contents of 3-Hydroxy-3-methylglutaric acid， indole-3-acetic acid（IAA）， gibberellin A7（GA7）， methyl jasmonate（MJA）， iP and IAA/ABA ratio， respectively， but significantly decreased the contents of glucuronic acid， gibberellin A3（GA3）， gibberellin A4（GA4）， total gibberellins（GAs）， 1-aminocyclopropanecarboxylic acid（ACC） and ACC/ABA ratio respectively， while it had no significant effect on the contents of succinic acid， butenedioic acid， malic acid， citric acid， malonic acid， pantothenic acid， nicotinic acid， pyroglutamic acid， suberic acid， phenylpyruvic acid， total organic acids， gibberellin A1（GA1）， jasmonic acid（JA）， JA-Ile， abscisic acid（ABA）， tZ， trans-zeatin-riboside（tZR）， N6-（Δ2-isopentenyl） adenosine（iPA）， total jasmonic acids（JAs）， cytokinin（CTK） and the ratios of GAs/ABA， JAs/ABA and CTK/ABA respectively. The principal component analysis showed that spraying NaHS solution significantly increased the contents of organic acid 3-hydroxy-3-methylglutaric acid and hormones MJA， GA7， tZ and IAA in leaves of naked oat under saline-alkali stress by 14.31%， 41.83%， 50.00%， 22.97% and 13.02%， respectively； while the contents of organic acids nicotinic acid， glucuronic acid and hormones GA4， ACC， tZR and GA3 were significantly decreased by 16.00%， 23.87%， 73.53%， 32.72%， 50.00% and 33.91%， respectively. In addition， the application of NaHS solution reduced the 1 000 grain weight of naked oat under saline-alkali stress by 5.91%， while spike number， boll number per spike， spike grain numbers and grain yield were increased by 2.19%， 9.70%， 61.60% and 52.83%， respectively. These results indicated that exogenous H2S participates in the regulation of organic acid and hormone levels of naked oat under salt-alkali stress， which could enhance the ability of naked oat to adapt to salt-alkali stress.
Photosynthesis is a basic metabolism process for plants and provides the material basis for plant growth and development. Different environmental conditions determine the polymorphism of plant photosynthetic capacity， but the mechanisms regulating the divergence of photosynthetic capacity among different populations under the same environmental conditions remain still unknown. This study aims to reveal the divergence of photosynthetic capacity in different geographical populations of Arabidopsis thaliana in Europe under common garden conditions and the mechanisms of their gene transcriptional regulation. A comparative study of photosynthetic characteristics of 23 geographic A. thaliana（Arabidopsis） populations from different regions was conducted under common garden conditions by determining the gas exchange parameters， chlorophyll fluorescence parameters and SPAD values. In addition， the photosynthetic-related gene expressions of the typical populations with differences in photosynthetic capacity was examined using real-time quantitative PCR（RT-qPCR）. The comparative result revealed that gas exchange parameters differed significantly among geographical populations of Arabidopsis from different climatic zones in Europe. The variation range of net photosynthetic rate was 2-11 μmol·m-2·s-1.while chlorophyll fluorescence parameters varied to a lesser extent， the variation range was almost no more than 10%. Cluster analysis showed that the 23 Arabidopsis populations were divided into two groups， strong and weak photosynthetic ability respectively. The populations with strong photosynthetic capacity were mainly distributed in central and western Europe， and the average net photosynthetic rate was 7.37 μmol·m-2·s-1. The populations with weak photosynthetic capacity were mainly distributed in eastern and southern Europe with an average net photosynthetic rate of 4.46 μmol·m-2·s-1. Correlation analysis revealed a significant correlation between net photosynthetic rate， water use efficiency and SPAD. The results of redundancy analysis（RDA） suggested that the divergence of photosynthetic capacity in Arabidopsis might be related to environmental factors such as temperature and rainfall during the growing season in the region. RT-qPCR results showed that the expression of PSⅡ- and Rubisco-related genes were significantly higher in En-D and Stw-0， typical populations with strong photosynthetic capacity， than in Wa-1 and Per-1， typical populations with weak photosynthetic capacity， suggesting that transcriptional differences in PSⅡ and Rubisco genes could be involved in the regulation of photosynthetic capacity differentiation in populations. The results clarified that there were differences in photosynthetic capacity between geographic populations of Arabidopsis under common gardens， and such differences might be related to the environment of origin and have been inherited to future generations during long-term evolution. In contrast， the transcriptional regulation of PSⅡ and Rubisco-related genes might be involved in the differentiation of photosynthetic capacity in Arabidopsis.
In order to provide a basis for the conservation and utilization of Michelia wilsonii natural population， the phenotypes of fruit and seed traits of M. wilsonii were analyzed， and the variation mechanism and spatial autocorrelation was studied. M. wilsonii natural population was taken as materials， which located in Zhougong Mountain， Ya’an， 12 phenotypic traits were determined. The spatial variation characteristics of fruits and seeds of M. wilsonii were explored by using coefficient of variation and semi-variogram. The results showed that：（1）The average coefficient of variation of phenotypic fruit and seed traits was 27.59%， the variation extent of morphological traits was the least， and the variation extent of seed traits was more abundant than that of fruit. （2）The seed abortion rate and follicle abortion rate were the highest in the lower part of fruit， which were 18.32% and 38.22% respectively. The seed and follicle abortion rates were lowest in the middle part of fruit， which were 15.05% and 23.45% respectively. （3）The semi-variogram models were dominated by exponential and spherical models， presenting a distribution of aggregation. Except fruit length， seed longitudinal diameter and seed abortion rate， the other nine indexes showed medium and high spatial autocorrelation respectively. （4）The anisotropy ratios of the nine indexes were close to 1， and the spatial heterogeneity was isotropy. Therefore， the phenotypic fruit and seed traits of M. wilsonii had abundant variation in the medium scale spatial range.
In order to clarify the characteristics and sequences variation of the chloroplast genome of Yucca， a comparative genomics of the chloroplasts was performed， and a phylogenetic tree based on the chloroplast genome was constructed. The chloroplast genome of Y. treculeana was obtained by high-throughput sequencing technology， and combined with the published chloroplast genome of Yucca， the chloroplast genomes of six species of Yucca were studied by comparative genomics， including basic structure， SSR， boundary contraction and expansion， sequence variation and phylogenetic analysis respectively. The results showed that the chloroplast genome size， gene type and number of the six Yucca species were similar， and the interspecific genome structure was conserved. Several repeated sequences were detected in the chloroplast genome of Yucca， among which SSR loci were mostly composed of mononucleotide， dinucleotide and tetranucleotide， and preferred A and T bases. Three regions with high variation（psbK-psbl-trnS-GCU， rpl20-rps12 and ccsA-ndhD） were identified from the chloroplast genomes of six Yucca species according to the nucleic acid polymorphism index（π）≥0.008. The phylogenetic relationships constructed from the chloroplast genome and LSC+SSC region sequences were basically consistent， and the phylogenetic relationships among six Yucca species were confirmed， among which Y. treculeana and Y. queretaroensis were most closely related. The sequencing obtained Y. treculeana chloroplast genome， revealed the genome characteristics and sequence variation of six Yucca species， and clarified the relatedness among various species. The results could provide reference for subsequent molecular marker development and phylogenetic research.
To clarify the basic characteristics of the complete chloroplast genome of Syringa villosa subsp. wolfii， the sequence information of chloroplast genome was analyzed by high-throughput sequencing technology， and its systematic evolution position was discussed. The results showed that：（1）The total length of the S. villosa subsp. wolfii chloroplast genome was 156 517 bp， which had a typical tetrad structure and had 131 functional genes， including 36 tRNA genes， 8 rRNA genes and 87 protein-coding genes respectively. （2）The relative synonymous codon usage（RSCU） analysis of the protein-coding region of the chloroplast genome showed that there were 31 codons with RSCU>1， of which 21 ended with A/U base； and there were 34 codons with RSCU<1， including 22 codons ending with G/C base. （3）In the chloroplast genome of S. villosa subsp. wolfii， 334 scattered repeats were detected， including 170 forward repeats and 164 palindromic repeats， and 227 SSR loci were discovered， and PCR primers were designed successfully for 226 of these loci. （4）Phylogenetic tree analysis based on the maximum likelihood method showed that S. villosa subsp. wolfii was the most closely to the S. yunnanensis. In this study， repeated sequences， IR boundaries and phylogeny of chloroplast genome of S. villosa subsp. wolfii were analyzed to provide reference data for molecular markers， phylogenetic classification， species identification and evaluation and DNA barcode development.
In order to clarify the potential functions of bZIP transcription factor family members in Macadamia integrifolia under stress response， MibZIP1 was cloned from ‘Guire 1’ fruit. Combined with the analysis of transcription factor structure and expression patterns under different treatments， it was found that the full length of MibZIP1 was 1 157 bp， and the ORF was 927 bp， and encoded 308 aa，and had a typical bZIP Superfamily domain. Phylogenetic analysis showed that MibZIP1， TsbZIP60 and NnbZIP60 were closely related. The results of tissue expression analysis showed that MibZIP1 expression was the lowest in leaves of ‘Guire 1’ and the highest in branches of ‘695’. The expression of MibZIP1 was significantly up-regulated in ‘Guire 1’ leaves treated by zeatin， salicylic acid， ethephon and abscisic acid respectively， but was unchanged treated by gibberellin and hydrogen peroxide respectively. It was speculated that MibZIP1 was related to the stress tolerance of M. integrifolia， which provided theoretical guidance for the development of new cultivation and hormone regulation techniques.
In order to reveal the driving mechanism of competition dynamics and pattern formation in the process of arid forest restoration and succession， the competition and spatial distribution pattern of standing trees in arid forest China were studied， and a typical secondary Pinus tabuliformis forests was investigated in the Ziwuling Mountains， China， and four larger sample sites（0.25 hm2 each） in different developmental stages were selected， according to the method using space instead of time， and some details of population， size， inter-tree competitions and spatial pattern of four sample sites were acquired respectively. The results showed that， in the four communities at different stages of succession， population densities of P. tabulaeformis were 1 476， 996， 800 and 648 per ha2 respectively； population densities of Betula platyphylla were 48， 32， 44 and 16 per ha2 respectively； and population densities of Populus davidiana were 64， 28， 24 and 12 per ha2 respectively. Competition index of main tree specials decreased with succession， and showed P. tabulaeformis>B. platyphylla>P. davidiana. Quantity of small individuals（diameter at breast height from 2-15 cm） decreased obviously； but quantity of large individuals（diameter at breast height larger than 30 cm） increased. In all succession stages， the competitive intensity of P. tabulaeformis decreased with the increase of diameter. The horizontal spatial competition pattern of P. tabulaeformis showed a patchiness distribution. P. tabulaeformis clumped at the scales 0-5 m， and negative correlated with other tress specials at the scales 5-15 m. Quantity of small size Pinus individuals decreased obvious in later developmental stage. Inter-tree competition of P. tabulaeformis was stronger than other tree species， and inter-tree competition decreased in the later developmental stage. The conclusions are as follows： the size of trees are negatively correlated with the competition index； the competition index of P. tabulaeformis is higher than other species； the competition at community scales decline as development， and the quantity and range of the patches with an intense competition decline， but do not disappear yet. Competition and spatial relations are observed within the scales of 5-15 m which are larger than the average crown size of Pinus. The conditions suggest that the range of inter-tree influence could expand indirectly beyond their crown range through unknown methods， which should be further investigated.
In order to clarify the reproductive biological characteristics of Dendrobium chrysanthum， the flowering habits， the pollen vitality， the characteristics of stigma secretion， the fruit setting rate as well as the development and storage of seed were investigated. The results were listed as followed： （1）Its budding period and the emergence were 19 d， 23 d respectively. The population's flowering period was 28d， whereas the single flower span was from 10-15 d. （2）From the first day to the third day of flowering， the pollen viability was about 90% but decreased to 23.7% at the ninth day of flowering. The data of pollen viability significantly differed between at three former day and other latter time（P<0.01）， pollen viability varied from high to low level with the blooming. （3）The stigma of D. chrysanthum produced secretions from the 2nd day of flowering， and had the maximum yield at the 6th day， and stigma staining showed that the stigma receptivity was optimal at the 5-6 d of flowering， and stigma receptivity changed from weak to strong to and then to weak with the prolongation of bloom stage. （4）An artificial pollination was made at the fourth day after flowering. but no fruit was found after cross-pollination and same-flower pollination. In the field， the seedpod weight was from 2.02-4.83 g， seed length varied from 0.628-0.845 mm and its width was from 0.082-0.110 mm， and the ratio of length to width was 7.798 and the rate of embryo formation reached to 97.35%， and the seed vigor was 90.80%， and the seed vigor maintained at 73.20% at room temperature for 6 months. All results mentioned above indicated that the flowering period of D. chrysanthum was short， and the pollen vigor remained the highest after flowering， and the pollen matured earlier than stigma. There was no apomixis occurred in D. chrysanthum， and the artifical self-pollination caused sterile. Although it could bear well-developed seedpods under natural condition with a high seed vitality. Dried seeds could keep a good storage resistance under natural condition. This study confirms the biological characteristics of flowering and dichogamy of D. chrysanthum， and its breeding system belongs to self-incompatibility， and could provide the strategies for conservation of wild germplasm resources and a precise hand-pollination of D. chrysanthum.
Since Linnaeus established the genus Populus， many taxonomic studies have been carried out about it and some taxonomic systems have been proposed， while the taxonomy of Populus is still in the stage of traditional morphological classification around the world. Although the taxonomic hierarchy of ‘genus-section-species’ is adopted in many countries， in which has Populus plant distributed， there are great differences in the classification of species， subspecies and varieties. The taxonomists of China and the United States are the representatives of splitter and lumper respectively， and there is a huge gap in poplar classification between them， but each has advantages and disadvantages. Even in China， there are still many problems to be solved. The existing phylogenetic studies about the genus Populus provide useful information to taxonomic revision， but the actual contribution is small yet. The ultimate aim on poplar classification is to establish a unified taxonomic system based on phylogeny in the world. It requires a comprehensive classification based on both population and the concepts of integrated species， which integrates morphology， ecology， biogeography， genomic bioinformatics and evolutionary biology.
Based on the survey of orchid resources in the lower Yarlung Zangbo River region， the priority protection value of each endangered plant was quantitatively calculated using multiple evaluation indexes to determine the endangerment level and priority protection sequence of rare and endangered orchids in the region by combining data collection and specimen review. The endangerment level of 156 species of endangered orchids in 60 genera in the lower Yarlung Zangbo River region was evaluated， among which 15 species were in critically endangered（CR） status， 46 species in endangered（EN） status， 78 species in vulnerable（VU） status and 17 species in near threatened（NT） status； the priority protection range value was 0.853 9-0.416 8， among which 45 species were classified as Class Ⅰ protected plants， 72 species as Class Ⅱ protected plants， and 39 species as Class Ⅲ protected plants.The results of this study differ greatly from the endangered degree and priority protection level of various protected plant lists， and most of the orchids are under enhanced threat in this region， which is consistent with the real survival status of these orchids in the lower Yarlung Zangbo River area， and the protection of orchids in this region is urgent and should be given sufficient attention.
In this study， the effects of NaCl， PEG（6000） and low temperature stresses on the levels of iATP （intracellular ATP） and eATP（extracellular ATP） of tobacco suspension cells BY-2（Nicotiana tabacum ‘Bright Yellow-2’） were studied respectively. The results showed that the tobacco suspension cells treated with 50-200 mmol·L-1 NaCl significantly increased membrane permeability（P<0.05）， the levels of iATP and eATP decreased significantly at 100 and 200 mmol·L-1 NaCl stresses（P<0.05）. With the increase of PEG mass concentration（50， 100 and 200 g·L-1）， the membrane permeability and eATP level increased. Under 200 g·L-1 PEG stress， eATP level increased significantly to 3.4-fold of the control（P<0.05）， iATP level decreased significantly to 0.5-fold of the control（P<0.05）. After the treatment with low temperature at 0-10 ℃， the membrane permeability and iATP level increased to different extents. iATP level increased to 1.9-fold of the control at 0 ℃， while eATP level decreased significantly to 0.8-fold the control at 10 ℃（P<0.05）. The above results indicate that iATP is the source of eATP in plant cells， iATP level is not the only factor that affects eATP level under abiotic stresses. The way in which plant cells transport ATP and other factors may affect eATP level under abiotic stresses.
To assess the size and complexity of the genome of the endangered plant Tetraenamongolica， and reveal the hyper-arid mechanism of T.mongolica and further explore its characteristic genetic resources， and to better decipher the whole genome information of T.mongolica， the second-generation high-throughput sequencing technology of genome survey analysis was used as the method， and bioinformatics method was used to estimate the genome information such as heterozygosity， repeat sequence and GC content of T.mongolica respectively. The results showed that the genome size of T. mongolica was 1 079.25 Mb， the corrected genome size was 1 065.84 Mb， and the heterozygosity rate was 0.76%， the percentage of repetitive sequences was 75.25%， and the GC content was 33.57% respectively. After the initial assembly of T. mongolica genome 3 502 126 contigs were obtained， totaling 682 Mb， with an N50 of 187 bp. It was hypothesized that T. mongolica genome belonged to a homo-tetraploid complex genome， which was difficult to assemble by whole-genome sequencing. Due to the high heterozygosity of T. mongolica， the third-generation high-throughput sequencing technology（single-molecule sequencing） combined with chromatin region capture technology could be used subsequently， which was expected to finally obtain a high-quality whole-genome map of T. mongolica.
At present， we still lack a deep understanding of the response direction and amplitude of root exudate flux and related ecological consequences to different nitrogen（N） deposition levels. In order to reveal the difference in the effects of different N addition treatments on root exudate C flux and its mediated soil nutrient transformation process， the typical Betula albosinensis Burk forest in the mountainous area of southwest China was used as materials， and different nitrogen deposition levels were simulated by in-situ N addition experiment（control group， 0 kg·hm-2?a-1）； low nitrogen treatment， 25 kg·hm-2?a-1； High nitrogen treatment， 50 kg·hm-2?a-1 respectively. The results showed that： （1）N addition significantly reduced the C input rate（the average root exudation rate per unit root biomass decreased by 14.87% under low nitrogen（N25））and annual C input flux of root exudates（about 45.01% reduction under low nitrogen condition）（P<0.05）， and high N treatment had stronger inhibition effect on root exudates C input. （2）N addition significantly inhibited soil N mineralization rate and related microbial extracellular enzyme activities（P<0.05）， and significantly reduced its rhizosphere effect. In conclusion， N deposition significantly inhibited the root exudates C flux and its mediated soil nutrient transformation process， and this inhibition effect increased with the increase of N deposition level. The results could enrich the understanding of carbon-nutrient cycling in forest under global climate change.
To explore the differences in the effects of on the growth and photosynthetic characteristics of tree seedlings， and their adaptation strategies to different nitrogen forms， the one-year seedlings of Fraxinus mandshurica and Quercus mongolica were used as materials， and three nitrogen fertilizer forms were applied： nitrate N， ammonium N and organic N. Two-way ANOVA was used to analysis the effect and interaction of nitrogen form and tree species on the growth and photosynthetic. Spearman rank correlation was used to analysis the correlation between growth index and photosynthetic index. The results were as follows， the effects of nitrogen form treatments， tree species and their interactions on the growth and physiological indexes of seedlings were significant（P<0.05） respectively. Photosynthesis rate and growth were significantly different between the two tree species in nitrogen forms（P<0.05）. The organic N treatment group was more beneficial to the growth of Q. mongolica， than the control group and other nitrogen form treatment groups； the growth indexes of F. mandshurica in the three nitrogen forms treatment groups were significantly higher than those in the control group（P<0.05）， but there was no significant difference in the growth indexes of F. mandshurica between the nitrogen form treatments（P>0.05）. Through the correlation analysis of the growth and physiological indicators of F. mandshurica and Q. mongolica， there was a significant positive correlation between the photosynthetic indexes of F. mandshurica， but the correlation between photosynthetic indexes and leaf nitrogen content was not significant（P>0.05）. The growth amount was significantly positively correlated with the light compensation point， light saturation points and dark respiration rate（P<0.05）； the maximum net photosynthetic rate of Q. mongolica was significantly positively correlated with the stomatal conductance（P<0.01）. The correlation between other photosynthetic indexes was not significant （P>0.05）， the maximum net photosynthetic rate was significantly positively correlated with leaf nitrogen content（P<0.001）， and high growth was negatively correlated with the maximum net photosynthetic rate and stomatal conductance relationship（P<0.01 and P<0.05）. Nitrogen forms and tree species and their interaction have significant effects on seedling growth and photosynthetic characteristics. Different tree species have different response strategies under different nitrogen forms. The organic nitrogen is more conducive to the growth of Q. mongolica， but nitrate nitrogen has a more obvious effect on the growth of F. mandshurica. The result of this study provides reference for the cultivation of appropriate nitrogen fertilizer in Northeast China.
To understand the effects of combined application of N and P on the stoichiometric characteristics of N， P and K in different organs（root， stem， leaf and sprout） of Pinus yunnanensis seedlings， the seasonal variation characteristics of the stoichiometric ratio of ω（N）∶ω（P）， ω（N）∶ω（K） and ω（P）∶ω（K） in different organs（root， stem， leaf and sprout） of P. yunnanensis seedlings were analyzed， and the seedlings of P. yunnanensis treated with different N and P were sampled and measured， and different fertilization experiments were carried out by using 3×3 regression design with 2 factors and 3 levels of N and P. The effects of combined application of N and P on the stoichiometric ratio of N， P and K in roots， leaves， stems and sprouts of P. yunnanensis after stumping were studied. The results showed that P. yunnanensis seedlings had no rule for the distribution of nutrient elements in different organs after flat stubble， but showed rich variation. With the change of fertilization season， ω（N）∶ω（P） decreased gradually in roots， stems and sprouts， and decreased first and then increased in leaves， but the overall difference was not significant. There were some differences in the effects of single application of N， P and combined application of N and P on the growth of P. yunnanensis seedlings. In general， the combined application of N and P was more beneficial to promote the growth of seedlings， and treatment No.5（N1P1） showed extremely significant（P<0.01）. The N， P and K stoichiometric ratios of all organs of seedlings were mainly influenced by the N×P interaction， followed by N and P was the least. The positive and negative correlations between ω（N）∶ω（P） and ω（N）∶ω（K） remained unchanged except in roots and leaves were changed， where the correlation between ω（N）∶ω（P） and ω（N）∶ω（K）. The correlations between ω（N）∶ω（P） and ω（P）∶ω（K）， ω（N）∶ω（K） and ω（P）∶ω（K） changed with seasonal changes in fertilizer application and the correlation coefficients decreased， regulated by P and K， respectively. Stumping changed the content of nutrient elements in the plant， and different fertilization treatments made significant differences in the stoichiometric characteristics of N， P and K in different organs of P. yunnanensis （P<0.01）. The combined application of N and P could effectively alleviate the limiting effect of single application of N and P on plants， and the nutrients was in a balanced state， and meet the needs of plant growth.
In order to illuminate population structures and dynamics of endangered mangrove species from genus Sonneratia，and provide a fundamental understanding and scientific basis for the protection and restoration of endangered mangrove species， the natural populations of three endangered mangrove species including Sonneratia × hainanensis， S. × gulngai， S. ovata were conducted as the research object， and the characteristics of population structure were described by establishing a static life table and drawing a population survival curve， and their future development trends were quantitatively described by population dynamic prediction and time series analysis respectively. The results showed that： （1）The populations structure of S. ovata was increasing type， while both S.× hainanensis and S. × gulngai were the declinated type due to the lack of young individuals. （2）The population survival curves of three endangered species showed the Deevey-Ⅱ type， and the mortality and disappearance curves of all populations showed the same trend， and showed a wavy line with the increase of age class. Both S.× hainanensis and S. × gulngai encountered obstacles in the aging stage， while S. ovata encountered bottlenecks in the development of young individuals. （3）The renewability of S.× hainanensis and S. × gulngai population was poor， and the population numbers would gradually decline in the future. The population of S. ovata had a good recovery potential， and the population number would increase gradually. However， if the population number of S. ovata decreased with the increase of age class， it might lead to the phenomenon of age class fault. （4）Human activities led to fragmentation of the original habitat， resulting in a series of environmental factors（light， salinity， tide， etc.） unsuitable for seed germination and seedling growth， which greatly inhibited the natural regeneration of the endangered species. Therefore， it would be recommended to step up efforts to protect the endangered natural populations in situ， optimization of ex situ conservation strategies and scientific implementation of field regression， carried out artificial assisted breeding to break through the problems of breeding， and ensured the normal renewal of the population.
Four species of Acer （A. mandshuricum， A. tataricum subsp. ginnala.， A. saccharum， A. pictum subsp. mono）on Mudanjang were selected as materials in spring， summer and autumn， respectively， and the seasonal variation trend of leaf traits（e.g. leaf thickness（TL）， stomata length（LS）， stomata width（WS）， stomata density（DS）， leaf vein density（DV）， specific leaf area（ASL） and pigment content） were analyzed， and the relationship between pigments and leaf morphological traits in different seasons were explored respectively. The result showed that： （1）Four kinds of Acer species showed higher TL， lower ASL and DS in summer， higher ASL and DV， lower TL in autumn. （2）The chlorophyll a and b of four Acer species were higher in summer， and the pigment content decreased in autumn. Their seasonal variation ranges were chlorophyll a 77.40%-98.80%， chlorophyll b 85.60%-99.53%， and carotenoids 4.29%-78.52%. （3）Pigment was closely related to leaf morphological traits. Under seasonal dynamics， pigments were positively correlated with ASL， DS and DV， and negatively correlated with TL， LS and WS（P<0.05）， but the correlations were slightly different in different seasons. The leaf was formed different construction strategies in response to climatic conditions in different seasons in four color species. The variation of leaf functional traits reflected the trade-off mechanism of colored-leaf plants adapting to seasonal changes.
In order to explore the response of seed germination and seedling growth of Armeniaca vulgaris to pulp and buried depth， and provide theoretical reference for natural regeneration and seedling cultivation of A. vulgaris， the seed germination and seedling growth of A. vulgaris were studied by seeds of two kinds of pericarp structure（pulp and no pulp） at different buried depths（14 gradients from surface to 18.0 cm）. The results showed that pulp and buried depth significantly affected seed germination， seedling growth and quality（P<0.05）. The buried depth <3.0 cm was not conducive to seedling， and the germination ability and seedling growth decreased with the increase of buried depth when buried depth >6.0 cm， 3.0-6.0 cm was the optimal buried depth， and the germination of seeds with no pulp was better than that of seeds with pulp， the germination rate， germination index， seedling rate and vigor index increased by 37.18 %， 3.88 %， 37.18 % and 26.59% respectively， seedling height， basal diameter， leaf number， root-shoot ratio and seedling quality index increased by 36.99%， 7.48%， 68.69%， 20.61% and 14.29%， respectively. The germination ability and seedling growth were significantly higher than those of pulpy seeds（P<0.05）. The seed germination and seedling growth indexes of pulp and no pulp seeds were significantly negatively correlated with buried depth（P<0.05）. The results showed that the no pulp seed had a certain promotion effect on seed germination and seedling growth of A. vulgaris， and the germination of seeds of A. vulgaris was optimal at the buried depth of 3.0-6.0 cm.
Grassland biodiversity played an important role in grassland ecosystem stability. In order to reveal the influence mechanism of soil physical and chemical properties on plant diversity of different management methods in grassland， and clarify the changes of species diversity and functional diversity， and the sample plots in the single-household management pasture（SMP） and multi-household management pasture（MMP） of plant community in Alpine Meadow of Gannan were surveyed respectively. The results indicated that： （1）The Margalef index， Simpson index， and Shannon-Winener index of the plant communities under MMP were significantly higher than those under SMP， while the Pielou index was not significantly different under different grazing management methods. （2）Under different management methods， the soil water content， the soil total nitrogen and the soil total phosphorus under MMP were significantly higher than those under SMP（P<0.05） respectively； the soil conductivity and soil pH under SMP were higher than those under MMP； with the deepening of soil layer， the soil water content， the soil total phosphorus， the soil total nitrogen， the soil organic carbon， and the soil conductivity were higher respectively， however the soil pH had no significant difference in the different soil layer. （3）The functional richness， functional evenness index， and functional dispersion under MMP were higher than those under SMP respectively， and the difference between SMP and MMP were significant（P<0.05）. （4）The correlation analysis showed that： the plant species diversity and functional diversity were significantly positively correlated with the soil water content， the soil total nitrogen， and the soil phosphorus， the soil conductivity and soil pH were significantly negatively correlated with plant species diversity and functional diversity. The redundancy analysis showed that： the effect of soil physicochemical properties on plant diversity was more significant under MMP， and the correlation between soil physicochemical properties and plant diversity were higher at the 0-10 cm soil layer. The soil total nitrogen and the soil organic carbon were significant influencing factors of plant diversity under SMP and the soil total nitrogen and the soil total phosphorus were significant influencing factors of plant diversity under MMP.
To reveal the strategies of plants in dealing with biotic and abiotic envrionmental factors through investigating responses of biomass allocation to soil water and population density at different growth stages， in this experiment， we subjected plants of an annual herbaceous species of Abutilon theophrasti to treatments of water addition and no addition（control）. Within each treatment， low， medium， and high densities were set up under field conditions， before measuring dry mass of root， stem， lamina， petiole and reproductive（flower and fruit） organs at day 20 and 50 of growth， to explore how biomass allocation of A. theophrasti respond to density and water addition， and effects of growth stage. Results showed at day 20， in water-added soil， compared to that at low density， medium density increased root mass ratio by 19.4% and root/shoot ratio by 21.5%， but decreased leaf mass ratio by 34.4%， with no response to density in biomass allocation in no-water-added soil（control）. At day 50， in controlled soil， high relative to low density reduced total biomass by 63.5%； in both water treatments， high relative to low density reduced root/shoot ratio and root mass ratio， but increased stem mass ratio， with total mass and allocations of other organs unaffected. Results suggest that the additon of water is more likely to promote the active response（increase） of root mass allocation to increased density at early stage， and mitigated passive responses（decrease） of total biomass at later stage. The responses of biomass allocation to density may depend on the strength of intraspecific interactions， and at the early stage moderate level of interactions among plants will more likely lead to facilitation underground， promoting the active responses of roots， and moderate interactions among plants at medium density can also promote active responses of roots to water addition. Growth stage can modify the strength of plant-plant interactions via affecting plant size， and further affect the responses of biomass allocation to density and water availability.
To explore the role of H2S signal in regulating stomatal movement in alfalfa and the relationship between H2S and Ca2+ during this process， wild type and the calcium transporter mutants of Medicago truncatula were used as experimental materials， and the transcriptional level， cellular level and physiological level were studied respectively， and the expression levels of related genes were compared by qRT-PCR， the content of Ca2+in vivo was detected by fluorescent probe， the content of H2S was measured by electrode method， and the stomatal aperture was observed by microscope respectively. The results showed that compared with the wild type， the content of H2S in the mutant NF3011 and NF2734 decreased significantly； the H2S signal inhibited the expression of calcium transporter encoding gene MTR_6g027580， the exogenous physiological concentration of H2S fumigation could induce stomatal closure of Medicago truncatula， and the combination of treatment with LaCl3， Ca2+ channel blocker， had no effect on stomatal movement of wild type， but opposite in mutant； the concentration of Ca2+ in guard cells was measured by fluorescence probe， which were consistent with the change law of stomatal aperture. In conclusion， the content of Ca2+ in guard cells of leaves is induced by H2S， whose stomatal aperture become smaller at the same time. In this process， the change of intracellular Ca2+ concentration mainly depend on Ca2+ transporter， and small partly depend on Ca2+ channel. The results of this study not only enrich the mechanism of H2S signaling in theory， but also have the potential to be applied to alfalfa production and other crops.
To reveal the function of transcription factor PsnbZIP1 from Populus simonii × P. nigra under abiotic stresses， P.simonii × P. nigra was used as material， and the PsnbZIP1 transcription factor gene was cloned with an ORF length of 432 bp， and the molecular mechanism of PsnbZIP1 under salt stress was analyzed. The expression pattern of PsnbZIP1 in P. simonii × P. nigra was analyzed under 150 mmol·L-1 NaCl by q-PCR， it was found that the expression of the gene increased rapidly. The PsnbZIP1 was predicted to be a hydrophilic unstable protein without trans-membrane structure but with signal peptide by bioinformatics analysis. The sub-cellular localization of the gene was observed by Agrobacterium mediated transient expression in tobacco. The results showed that the gene was a nuclear localization protein. It was confirmed by Y2HGold yeast competent cells that the gene had no transcriptional activation activity in yeast. The analysis of the promoter sequence of the PsnbZIP1 gene showed that the promoter contained auxin response elements， ABA response elements， light response elements and seed-specific cis-acting regulatory elements respectively， which might play a role in plant growth and development and response to stress.The promoter also included the MYB binding site and MYBHv1 binding site involved in drought induction， indicating that the gene was likely to interact with some of MYB involved in drought induction.
To reveal the role of transcription factor PsnbHLH162 of Populus simonii × P. nigra under abiotic stresses， and to explore the signal transduction process of genes in plants， the signal transduction process of this gene in plants is explored to provide the theoretical basis for the acquisition of excellent stress-resistant tree species in the future. In this experiment， PsnbHLH162 gene was cloned and obtained from P. simonii × P. nigra as material， and the target gene and promoter were analyzed by bioinformatics； and the function of genes in response to abiotic stresses was analyzed by fluorescence quantitative PCR. The results showed that the cDNA of PsnbHLH162 gene was 537 bp， and the N-terminal of the gene contained a highly conserved HLH domain， and the encoded protein might be a stable hydrophilic protein without trans-membrane region， localized in the nucleus and had no transcriptional activation activity. The promoter region contained a variety of ABA-responsive， auxin-responsive， light-responsive and circadian elements， confirming that this gene participated in abiotic stress response. The results of fluorescence quantitative PCR showed that under salt stress， the gene expression in root tissue was the highest compared with stem and leaf tissue； under low temperature stress， gene expression in stem tissue was the highest compared with leaf and root tissue. It was found that the expression of PsnbHLH162 could be induced by salt and low temperature in plants.
In order to illustrate the flowering characteristics and sexual reproduction of the rare and endangered plant Sinojackia microcarpa， the morphological characteristics of flower， flowering dynamics， pollen ovule ratio（P/O）， stigma receptivity， pollen viability， bagging experiment， pollinator insects and pollinator frequency were investigated respectively. The results showed that： （1）the hybridization index（OCI） was four， the flowering period was 5-7 d， and the flowering period of the population lasted 20 d. Pollen to ovule ratio was 4 093.21±498.56. The pollen viability was the highest on the third day after flowering（76.21%）， but the lowest on the seventh day after flowering（18.37%）. The most suitable period of stigmas was on the second day after flowering. （2）The bagging result showed that： there were some self-incompatibility and no apomictic reproduction in S. microcarpa. Pollinators were necessary for the reproductive process of S. microcarpa， and cross-pollination could improve the rate of fruit and seed setting. There were seven species， five families and three orders in the visiting insects of S. microcarpa. The main pollinators were Xylocopa appendiculata， Bombus sp.，Vespa sp.，Apis cerana，Episyrphus balteatus. The average pollinator frequency of Bombus sp. was （8.67±0.21） times per hour. Further research on the biological characteristics of flowering and breeding system of this species would be helpful to further explore the mechanism of its endangerment， and provided theoretical basis and reference for future studies on rare and endangered plants.
Root hairs are tubular extensions of plant root epidermal cells that play vital roles in soil fixation， water and inorganic salts absorption， and information exchange between plant roots and outside world. The developmental processes of root hair are highly plastic and might easily be affected by various plant hormones and environmental factors. Due to the structural and functional characteristics of root hair， it is often used as model to study apical growth and fate determination of plant cells. Therefore， the regulatory mechanism of root hair development has been a hot topic in the field of botany. The review summarized the research progress in the field of root hair development in the past two decades.
The effect of sampling time and plant growth regulators on the induction of callus， somatic embryo and adventitious bud were investigated with immature embryos of Iris lacteal var. chinensis as explants. The results showed that the most feasible sampling time for immature embryos was 35-45 d after pollination， the young embryos were fully developed， but the endosperm was not completely hardened， and the young embryo was easy to dissect. The optimum medium for callus induction was MS+1.0 mg·L-1 2，4-D+0.2 mg·L-1 6-BA with the induction rate of 83.33%. The appropriate medium for somatic cell induction was MS+0.25 mg·L-1 2，4-D+0.05 mg·L-1 6-BA with the induction rate of 71.67%. The most suitable medium for adventitious bud induction and proliferation was MS+0.2 mg·L-1 TDZ+0.05 mg·L-1 NAA with the induction rate of 78.33% and proliferation coefficient 3.65 in this experiment. The rooting rate was more than 95% after four weeks cultivation on MS medium supplemented with 0.1 mg·L-1 NAA. Then， the medium was washed off and explants were transplanted to sterilized vermiculite， and the survival rate was more than 95%. This study has established an efficient regeneration system of I. lacteal var. chinensis embryos， which can lay a foundation for genetic transformation and gene function analysis of I. lacteal var. chinensis.
Transcriptome analysis in Populus simonii × P. nigra overexpressing PsnCycD1；1 showed PsnHB3 and PsnHB15 are differential genes. Analysis of PsnHB13 and PsnHB15 conservative domains through InterPro tool. The STRING software was utilized to explore PsnHB13 and PsnHB15 proteins interaction network analysis. Yeast two hybrid was used to verify the interaction proteins，calculate the ratio of leaf length to width，the ratio of dry weight to fresh weight of leaves and stems of transgenic plants，and analyze the transcriptome of PsnHB13 overexpression plants. Conserved domain analysis showed that PsnHB13 and PsnHB15 genes belonged two subfamilies，showing that PsnHB13 mainly contains the HDZip I domain，and PsnHB15 mainly contains the HDZip Ⅲ domain. ，Each gene is screened to 10 interacting genes. Moreover，PsnHB15 has a higher probability of interaction with family proteins. Yeast two-hybrid assays demonstrated that PsnHB15 interacts with PsnHB13 and PsnHB13 interacts with PsnCycD1；1. The aspect ratio of leaves in transgenic lines overexpressing PsnHB13 and PsnHB15 increased in the early seedling stage.The ratio of dry weight to fresh weight in stems of PsnHB13 overexpression lines increased significantly（P<0.05）. The analysis of the transcriptome revealed that Gene Ontologies（GO） enrichment analysis identified 3 significantly enriched GO terms，including response to chemical，response to organic substance，regulation of RNA metabolic process. KEGG pathway enrichment analysis demonstrated that transcription factors，plant hormone signal transduction and Cytochrome P450 were significantly enriched. These differential genes，including MADS-box transcription factor，MYBP transcription factor，ERF1 transcription factor，GH3 auxin responsive genes，SAUR protein family. PsnHB13 and PsnHB15 play an important role in the growth and development of Populus simonii × P. nigra，and are key genes to explore the growth law of plants and reveal the relationship between cell cycle and growth regulation.
To explore the bryophyte diversity of underground forests in craters of Jingpohu Global Geopark， the typical investigation method was used， and a total of 3 622 bryophyte specimens were collected， and morphological and anatomical methods were used to identify the specimens. The results showed that， 292 species（126 genera and 53 families） were recorded， 31 species （17 genera and 14 families） were liverworts， 261 species （109 genera and 39 families） were mosses. The number of bryophyte species of four craters was 192 species in Ⅳ， 126 species in Ⅰ， 113 species in Ⅲ， and 61 species in Ⅱ， respectively. The dominant families were Brachytheciaceae， Mniaceae， Pottiaceae， etc.， accounting for 42.12% of the total species， and the dominant genera were Brachythecium， Entodon， Plagiomnium， etc.， accounting for 18.49% of the total species， and the dominant species were Pylaisia polyantha， Pylaisiadelpha yokohamae， Entodon flavescens， respectively. There were 20 common species of bryophytes in four craters， and the unique species in the Ⅳ crater was the most（88 species）. The diversity of the ‘moderate interference hypothesis’ was supported， and the similarity of bryophytes between Jingpo Lake crater and Wudalianchi volcanos was high（20.42%）， which revealed that the terrain contributes greatly to the diversity. The alpha diversity of bryophytes in the crater I exhibited a mid-peak pattern， which was in line with the ‘Mid-elevation bulge’ theory， priority should be given to the central elevation where the bryophytes were the most abundant. The study showed that the underground forests in Jingpohu Global Geopark craters preserved high bryophyte diversity and played an important role in the volcanic ecosystem of China， and a key protection should be given to bryophytes in this volcanic geological wonder to preserve genetic resources， and the results provided first-hand basic information and important scientific significance.
To explore the effects of exogenous hormones soaking combined with polyethylene glycol 6000 （PEG） osmotic treatment on the thermal dormancy and related physiological changes in seeds of Fraxinus mandshurica， non-dormant F. mandshurica seeds were used as materials and then soaked with 1 mmol·L-1 gibberellin（GA4+7）， ethylene（ETH） and cytokinins（6-BA） for 24 h respectively， and the germination of seeds cultured in different mass fractions（0， 5%， 25%， 50%） PEG solution at the induction thermal dormancy temperature（25 ℃）for 7 d and then at 10 ℃ was assayed. On this basis， the treatments with significant results were selected to determine the changes in seeds endogenous hormones content and cell wall degrading enzyme activity. The results showed that： compared with hormone treatment alone， GA4+7 combined with different mass fraction PEG had no significant effect on germination ability. With the increase of PEG mass fraction， the germination ability of 6-BA combined with PEG treatment gradually increased and then tend to stabilized， when combined with 25% PEG， the germination percentage and germination index respectively increased 69.31% and 1.04， and the germination time was shortened by 7.8 d. The seeds germination ability treated ETH combined with PEG gradually increased with the increase of PEG mass fraction， when combined with 50% PEG， the germination percentage and germination index respectively increased 43.43% and 0.76. Hormone combined with osmotic treatment significantly increased endosperm cellulase activity， but the GA and ABA contents in embryo and endosperm were not significantly regularity. In conclusion， exogenous hormone combined with osmotic treatment could reduce the thermal dormancy of F. mandshurica seeds， and the effect was different depending on the hormone species.
To investigate the effects of salicylic acid（SA） on growth and secondary production synthesis of Betula platyphylla seedling under saline alkali stress， three treatments were applied to birch seedlings： water treatment（control）， 200 mmol·L-1 NaHCO3， 200 mmol·L-1 NaHCO3+360 μmol·L-1 SA. The relative conductivity， chlorophyll fluorescence parameters， osmotic content， anti-stress enzyme activity， the relative expression of key genes of triterpene synthesis pathway in the middle leaves of birch seedlings in response to different treatments were detected respectively， and the total triterpenoids， flavonoids and polyphenols of birch seedlings were analyzed. The results showed that： ①under the 200 mmol·L-1 NaHCO3 treatment， then 360 μmol·L-1 SA treatment significantly reduced the relative conductivity of the leaves of birch seedlings， improved the Fv/Fm value of chlorophyll fluorescence parameters of birch seedlings， increased the content of the osmotic regulator proline and soluble protein， and enhanced the activities of antioxidant enzymes（SOD， POD， CAT， APX） in birch seedlings to a certain extent. ②200 mmol·L-1 NaHCO3 saline alkali stress promoted the upregulation of the expression of key genes of triterpene synthesis pathway FPS， SS， SE， BPX and BPW in birch seedlings， and significantly promoted the synthesis of polyphenols in birch seedlings in the early stage， and significantly promoted the accumulation of total triterpenoids and flavonoids in the late stage of saline-alkali stress（P<0.05）. The application of SA under saline-alkali stress promoted the upregulation of HMGR， FPS， SE， and BPX gene expression in birch seedlings， and promoted the synthesis of flavonoids in the early stage of stress， and significantly promoted the accumulation of total triterpenes in the late stage of stress， which was 34% higher than that of the saline-alkali stress group and 47% higher than that of the water treatment on 7th day. Overall， under saline-alkali stress， SA with suitable concentration improves the tolerance to saline-alkali of birch seedlings by adjusting osmotic equilibrium， alleviating light inhibition， enhancing the antioxidant defense system of birch seedlings， and regulating substance metabolism.
To investigate the effects of salicylic acid（SA）， nano-zinc oxide（ZnO NPs） and growth-promoting endophytic fungus YZ13-1（Fusarium graminearum） on drought tolerance of Fraxinus mandshurica seedlings. Two years old potted F. mandshurica seedlings were used as materials and 5 groups of treatments were set in this experiment：T1，drought stress treatment （soil water content was 20%-25%）； T2， T3 and T4 groups were additionally treated with 50 mg·L-1 SA，100 mg·L-1 ZnO NPs， growth-promoting fungus YZ13-1 suspension on the basis of T1 group； CK， control group（soil water content was 50%-55%）. The results showed that compared with T1 group， the activities of peroxidase（POD）， ascorbate peroxidase（APX）， catalase（CAT） were increased by 2 times， soluble sugar（SS）， proline（PRO） and phenolic substances increased by 44%， 60%， 16%， and relative electrical conductivity（RWC） of leaves decreased by 14% in T2 group. Compared with endophytic fungi and ZnO NPs， SA could significantly increase the anti-stress enzyme activity， increase the contents of osmotic substances and phenolic substances， and thus improve the drought resistance ability of F. mandshurica under drought stress. The study clarified that three induction treatments could improve the drought resistance of F. mandshurica， and SA treatment was the best， providing a theoretical basis for screening drought resistance agents of F. mandshurica.
