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 explore the flowering strategies of early spring flowering plants at low temperatures， five early spring flowering plants and five non-early spring flowering plants were collected，and the endogenous hormones and secondary metabolites between early spring flowering plants and non-early spring flowering plants were analyzed by high performance liquid chromatography-mass spectrometry and metabolomics. The results showed that the content of auxin（IAA） and zeatin（ZT） in early spring flowering plants were significantly lower than that in non-early spring flowering plants， while gibberellin（GA3） and abscisic acid（ABA） were significantly higher than that in non-early spring flowering plants， indicated that GA3 and ABA might play a regulatory role in promoting the flowering process of early spring plants. In the secondary metabolites， L-phenylalanine， the precursor of phenolic metabolites， was usually higher in non-early spring flowering plants than in early spring flowering plants. In addition， there were C6C1 phenolic compounds， including vanillic acid， syringic acid and protocatechuic acid； C6C3 phenolic compounds， including ferulic acid， chlorogenic acid and caffeic acid； Flavonoids， including apigenin， genistein， hesperidin， chrysin and galangin， were generally higher in non-early spring flowering plants than in early spring flowering plants. The changes of these secondary metabolites might be due to a large amount of material loss caused by the flowering process of flowering plants in early spring， which reduced the level of secondary metabolism. The results showed that endogenous plant hormones and secondary metabolites regulated the physiological process of flowering plants in early spring， and laid a foundation for further understanding the flowering process of plants under low temperatures.
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.
In order to promote the rapid greening of the steep bare rock slopes in the Jiuzhaigou National Nature Reserve after the earthquake， and accelerate the ecological restoration process of the landscape， based on references and field investigations， 30 common native mosses in the region were selected， and an evaluation index system of 18 items was constructed based on six aspects including resistance ability， availability， ecological function， reproductive ability， biomass accumulation， and aesthetic appeal， using the Analytic Hierarchy Process（AHP）. The results indicated that： according to the comprehensive evaluation score， the mosses were divided into four grades. Finally， five species， Racomitrium japonicum， Hypnum plumaeforme， Eurohypnum leptothollum， Plagiomnium ellipticum and Brachythecium rutabulum were selected. The results should provide an objective guidance for future ecological restoration without soil in Jiuzhaigou and its surrounding cold fragile ecosystem area.
To explore a sustainable and stable way to obtain birch branches， a multi branch birch by promoting germination was established. One year old birch seedlings were used as experimental materials， and three cutting heights（10， 20 and 30 cm）and four hormone or chemical agents （20 mg·L-1 2，4-D， 20 mg·L-1 KT， 20 mg·L-1 6-BA and 20 mg·L-1 KMnO4） were used to promote the sprouting of birch seedlings. The results showed that the germination rate of birch seedlings was the highest， which reached 65.0% after the first cutting（30 d） and the cutting height was 10 cm. Under the treatment of sawdust moisture， the sprouting rate and sprouting yield of the three cutting heights were higher， the sprouting rate was more than 75.0%， and the yield was more than 77.0 g per plant. The content of total triterpenoids in the branches was the highest at 20 cm cutting height（76.43 mg·g-1）， followed by 10 cm cutting height. Other treatments were not conducive to the accumulation of total triterpenoids. The content of total triterpenoids in leaves was the highest under the treatment of 6-BA （91.16 mg·g-1）， which was more than 2.68 times of sawdust treatment（30 cm）. The content of total triterpenoids in the branches and leaves of sawdust， KT and KMnO4 treatments was significantly lower than that of other treatments. 6-BA was beneficial to the accumulation of oleanolic acid in branches and leaves， while other treatments were not conducive to the accumulation of oleanolic acid. Sawdust treatment was beneficial to the secondary sprouting and yield improvement. The sprouting yield of the treatment with 10 cm cutting height reached 126.96 g per plant. The total triterpenoids content in the branches was 97.99 mg·g-1 when treated with 6-BA at the cutting height of 30 cm. The content of total triterpenoids in leaves was option when the cutting height was 20 cm， reaching 99.22 mg·g-1， followed by sawdust treatment group. The results provid technical support for sustainable and efficient utilization of birch resources and obtaining triterpenoids.
In order to illuminate the regulating mechanism of gas signal hydrogen sulfide（H2S） on reactive oxygen species（ROS） metabolism of naked oat（Avena nuda） under saline-alkali stress， and to screen and determine the optimal application period and concentration of H2S， the effect of spraying NaHS（H2S donor； 0， 25， 50， 100， 200 and 400 μmol·L-1） at different periods（seedling stage， jointing stage， heading stage， flowering stage and filling stage） on the H2S content， H2S production related enzyme activityof L-cysteine desulfhydrylase（LCD） and ROS metabolism-related enzyme activities and substance contents in leaves of soil-potted naked oat under 3.0 g·kg-1 salt-alkali mixed stress（NaCl∶Na2SO4∶NaHCO3∶Na2CO3 molar ratio was 12∶8∶9∶1） were carried out respectively. The results showed that spraying period， NaHS concentration and their interaction had significant effects on the content of H2S， superoxide anion（）， hydrogen peroxide（H2O2）， malondialdehyde（MDA）， ascorbic acid（AsA） and glutathione（GSH）， and the activities of LCD， superoxide dismutase（SOD）， catalase（CAT）， peroxidase（POD）， ascorbic acid peroxidase（APX） and glutathione reductase（GR） in naked oat leaves under salt-alkali stress respectively. Compared with spraying 0 μmol?L-1 NaHS， spraying a certain concentration of NaHS increased the contents of H2S， AsA，GSH and the activities of LCD， SOD， CAT， POD， APX and GR， and reduced the accumulation of ， H2O2 and MDA respectively. However， the optimal spraying period and NaHS concentration of the above indexes were different. Comprehensive analysis of membership function showed that spraying 25-200 μmol?L-1 NaHS at the seedling stage and jointing stage had the highest the comprehensive evaluation value（D）. It indicated that spraying 25-200 μmol?L-1 NaHS at the seedling-joint stage improved the ROS scavenging ability， alleviated the oxidative damage of salt-alkali stress on naked oats.
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.
Platycladus orientalis ‘Beverleyensis’ is an important ornamental tree species. Plant endogenous hormones（i.e.， indole-3-acetic acid（IAA）， zeatin（ZT）， abscisic acid（ABA） and jasmonic（JA）） play an important role in regulating the adventitious roots regeneration process， but the dynamic changes of endogenous hormones at different developmental stages and their effects on adventitious roots are still unclear. Using semi-woody branches as materials， the dynamic changes of four endogenous hormones were detected by high performance liquid chromatography- mass spectrum（LC-MS）. The results showed that the root primordium originated from callus， medullary ray， xylem， vascular cambium， secondary phloem， cortex， and the junction of medullary ray and cambium respectively， which belonged to multiple locus occurrence mode and the multiple rooting type. Hormonal dynamics results showed that the content of IAA and ZT decreased， ABA and JA increased with the formation of callus； the content of IAA and ZT increased slowly， ABA and JA decreased with the differentiation of root primordium； IAA， ZT， JA gradually increased， and ABA maintained at a low level during adventitious root formation and elongation. Hormone balance analysis results showed that the IAA/ABA ratio and IAA/JA ratio both decreased， and the increasing of IAA/ZT ratio was beneficial to the formation of callus， and on the contrary， it was beneficial to the induction and differentiation of root primordia， while the IAA/ABA ratio increased， IAA/ZT and IAA/ JA maintained at a low level was conducive to the formation and elongation of adventitious roots. The results provide a basis for revealing the regulation effect of different endogenous hormones on the development of adventitious roots of P. orientalis ‘Beverleyensis’.
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 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.
In this paper， the zygotic embryos were used as storage materials to further analyze the changes of physiological and biochemical indexes of the zygotic embryos before and after cryopreservation， and the effects of freezing method and dewatering time on physiological and biochemical indexes were clarified， which provided physiological data support for the establishment of long-term storage methods of fine genetic materials of Fraxinus mandshurica. Under the condition of dehydration for 120 min， the activity of dehydrogenase in zygote embryos was the highest， and the activity of catalase， peroxidase and mass fraction of proline reached the maximum. They were 1 168.85 U·g-1·min-1， 338.33 U·g-1·min-1 and 394.99 μg·g-1， respectively. Dehydrogenase activity， proline content， peroxidase activity and catalase activity in zygotic embryo cells were all the minimum values after vitrification. The soluble protein fraction and superoxide dismutase activity in zygote embryos reached the maximum values after storage by slow freezing method， which were 18.82 mg·g-1 and 361.97 U·g-1， respectively， which were significantly higher than those by other freezing methods. The activity of zygotic embryos reached the highest value under the conditions of drying and dewatering for 120 min and fast freezing. The results showed that the survival rate and physiological indexes of the zygotic embryos of F. mandshurica were affected by different freezing methods， dehydration time and their interaction. In addition to the decrease of malondialdehyde content， the dehydrogenase activity， antioxidant enzyme activity， proline content and soluble protein content in the zygotic embryo cells of F. mandshurica increased with the increase of dehydration time after being stored in different freezing methods. The survival rates of zygotic embryos and somatic embryos after cryopreservation were 62.26% and 51.68%. Therefore， the method of drying and dewatering for 120 min combined with fast freezing is suitable for cryopreservation of F. mandshurica embryos.
To explore the optimal cryopreservation conditions for Sinopodophyllum hexandrum seeds， and to provide technical support for the long-term preservation of S. hexandrum seeds， four kinds of seeds with different moisture contents（1.6％， 9.6％， 20.9％ and 30.5％） were obtained by silica gel drying， natural shade drying and soaking methods， and cryopreserved by direct freezing， slow freezing and vitrification respectively， and the seed viability and the activity of superoxide dismutase（SOD）， peroxidase（POD）， and the contents of malondialdehyde（MDA）， total protein（TP）， soluble starch and soluble sugar in seeds were measured before and after cryopreservation respectively. The results showed that the seed viability of S. hexandrum seeds with different water content declined in varying degrees after three cryopreservation methods， but the seeds with water content of 1.6%， 9.6% and 20.9% had no significant difference compared with the control group（P>0.05）. After cryopreservation， the contents of soluble sugar and total protein in S. hexandrum seeds with four kinds of water content increased， and the content of soluble sugar was the biggest， while the content of starch in seeds showed a downward trend as a whole， and the activities of superoxide dismutase and peroxidase declined slightly when the water content was 1.6% and 9.6%. The content of MDA increased when the water content was 1.6% and 30.5%， but decreased when the water content was 9.6% and 20.9%， indicating that the seeds with different water content were damaged to different degrees after freezing in liquid nitrogen. The activities of antioxidant enzymes decreased， while the increase of protein content and the accumulation of soluble sugar content caused by starch degradation improved the low temperature tolerance of seeds. As a result， the content of malondialdehyde（MDA） in chilling injury products showed different trends. The seeds of vitrification freezing group with 1.6% water content and seeds of direct freezing group and slow freezing group with 9.6% water content were the top three places by entropy weight TOPSIS. The results showed that the liquid nitrogen cryopreservation technology of S. hexandrum seeds could be feasible， and the seeds with 9.6% water content would be the best cryopreservation conditions by direct freezing or slow freezing.
To provide an effective supplement for ecological restoration technology in the Arsenic sandstone area， the microecological soil environment in Pinus tabulaeformis and Caragana korshinskii plantation， naturally restored grassland， and abandoned land were studied respectively. The changes in microbial community structure and microbial biomass carbon， nitrogen and phosphorus contents， soil enzyme activities related to nutrient conversion， and soil chemical properties were analyzed in different vegetation types. The correlation between soil microbial community structure and soil microecological environment was discussed， then the main influencing factors of soil microhabitat types were explored in different ecological restoration vegetation. The results showed that： （1）The soil dissolved organic carbon（C） content of P. tabulaeformis plantation was the highest of the four vegetation types， which was 4.26 mg·kg-1. The soil available nitrogen（N） content of the C. korshinskii plantation was the highest， which was 11.69 mg·kg-1. However， there was no significant difference in soil available phosphorus（P） content among P. tabulaeformis plantation， C. korshinskii plantation and natural restored grassland. （2）The enzyme activities related to nutrient conversion and soil microbial biomass C， N and P of P. tabulaeformis plantation were significantly higher than those of other vegetation types. （3）The relative abundance of soil fungi was the highest in P. tabulaeformis plantation， which was 31.36%. The relative abundance of Gram-positive bacteria in the soil of the C. korshinskii plantation and abandoned land was the highest， which were 35.73% and 37.27%. The relative abundance of soil Gram-negative bacteria increased with the decrease of available organic C. It was the lowest in P. tabulaeformis plantation（36.82%） and the highest in the natural restored grassland（42.13%）. （4）The relative abundance of soil fungi was positively correlated with enzyme activities related to nutrient conversion. Gram-negative bacteria of preferred unstable C sources were less correlated with soil microecological environmental factors. Still， Gram-positive bacteria were significantly negatively correlated with the indexes of soil C conversion. （5）The Redundancy analysis showed that alkaline phosphatase was the most explainable environmental factor， and it was positively correlated with fungi and negatively correlated with Gram-positive bacteria（P<0.01）. In conclusion， the stability of the microecological environment of P. tabulaeformis plantation was relatively high in the ecological restoration vegetation types of the Arsenic sandstone area， which might be used as the optimal ecological restoration tree species in the Arsenic sandstone area. The synergistic effect of alkaline phosphatase and fungi in rhizosphere soil microecological environment might effectively regulate environmental restoration in Arsenic sandstone areas.
To explore the leaf color mechanism of Acer negundo ‘Aurea’， and to provide theoretical basis for the leaf color mechanism and cultivation of golden leaf plants， the golden re-green and green leaves of A. negundo ‘Aurea’ were used as materials， the leaf color parameters， pigment content and anatomy structure of three leaf types were measured and compared. The results showed that the leaf color parameters L*， a*， b* of the golden leaves were significantly higher than re-green leaves and CK（P<0.01）. The leaf color parameters of A. negundo ‘Aurea’ showed a downward trend during the process of re-greening. The chlorophyll a， chlorophyll b， total chlorophyll and， carotenoid content of the golden leaves were significantly lower than re-green leaves and CK， ω（carotenoid）/ω（total chlorophyll） was 0.64， which was significantly higher than re-green leaves and CK（P<0.01）， and pigment content of the golden leaves increased during the process of re-green. The cross-section structure of the three types leaves were different in the thickness， the ratio and arrangement of tissue. The thickness of golden leaves was 124.51 μm， which was significantly lower than that of CK（P<0.05）. The palisade tissue thickness of 31.26 μm and the palisade/spongy ratio of 0.45 in the golden leaves were significantly lower than other two types of leaves（P<0.01）， the palisade tissue and spongy tissue were arranged irregularly and disorderly， while the other two leaf types were arranged regularly and orderly； The chloroplast length and width were 3.42 μm and 1.27 μm respectively， which were significantly smaller than the re-green leaves and CK（P<0.01）， the chloroplast volume was small and incomplete， lacking thylakoid stacks. The high ω（carotenoid）/ω（total chlorophyll）， thinner palisade tissue， lower palisade/spongy ratio and lack of stacking of thylakoid in chloroplasts were the reasons for the golden color leaves of A. negundo ‘Aurea’.
Abies beshanzuensis is a critically endangered plant endemic species in Baishanzu Mountain， Zhejiang Province， and only three mother trees are remained， one is scattered， and the other two grow adjacent to the north and south. In order to understand the spatial-temporal pattern of the seed rain of A. beshanzuensis， 33 seed collection frames were set up to collect the seeds produced in 2017 and 2019 once every half month. The results showed that： （1）From December 16th， 2017 to February 28th， 2018， 1 093 seeds from the scattered tree and 1 020 seeds from two adjacent trees were collected using six times， while from November 31th， 2019 to January 16th， 2020， 341 seeds from scattered tree and 165 seeds from the adjacent north tree were collected using four times. （2）The fresh weight of 1 000 seeds of A. beshanzuensis varied greatly， with the minimum of two adjacent trees seeds in 2017（25.87 g） and the maximum of the adjacent north tree seeds in 2019（39.21 g）. The maximum length， width and thickness of the seeds were 14.5， 6.8 and 4.1 mm respectively， and the maximum length and width of the seed wings were 16.4 and 13.7 mm respectively. Both seed plumpness rate and 1 000-seed mass showed a trend of “decreasing first and then increasing”. The seed wing， seed plumpness， and seed fresh weight were larger in the north direction， whereas those in the south direction were smaller. There was no obvious pattern between seed characters and the distance from the collection frames. （3）In 2017， there were two peaks of seed rain， and the seeds collected in the first two times were about 80% of the total. However， in 2019， there was only one peak of seed rain， and the seeds collected for the first time were about 80% of the total. After the peak， the number of seeds collected decreased significantly. There was a phenomenon of “secondary seed drop”， which prolonged the drop time of seeds. （4） The number of seeds collected decreased with the increases of the distance from the collection frame to the mother tree， 98% of seeds fell within 10 m from the mother tree. Only four seeds were collected in the 30 m frames. （5） The number of seeds collected from the west was the largest， which might be related to the lower terrain in the west direction.
In order to investigate the effects of saline-alkali stress on the plant growth， seedling of Heucheramicrantha ‘Silver Fan’ was used as materials， and 30， 60， 90， 120 and 150 mmol·L-1 NaCl and NaHCO3， and 20， 30， 40， 50 and 60 mmol·L-1 Na2CO3， were used to simulate salt stress， salt alkali stress， and alkali stress， respectively. The experiment used 1/4 Hoagland nutrient solution as the control， and used water culture method to treat seedlings for 0， 7 and 14 d. The response of plants was observed from aspects such as salt damage rate and physiological indicators， and the effects of salt stress on the growth of ‘Silver Fan’ seedlings were analyzed and evaluated by principal component analysis of 7 indicators. The results showed that under different salt alkali stress treatments， the relative conductivity and malondialdehyde content（MDA） of the seedlings showed an increasing trend with time and concentration. The seedlings treated with 30 mmol·L-1 NaCl or NaHCO3 showed no obvious symptoms of salt damage， and all physiological indicators showed an upward trend with the prolongation of treatment time； With the increase of concentration and stress time， the salt damage index of seedlings increased， but the ornamental value decreased. The overall trend of superoxide dismutase（SOD） increased first and then decreased， reaching the maximum value at 90 mmol·L-1 NaCl and 60 mmol·L-1 NaHCO3， respectively. Under the same stress time， the contents of chlorophyll（Chl）， chlorophyll a（Chla）， and chlorophyll b（Chlb） decreased continuously， while ρ（Chla）/ρ（Chlb） increased with the increase of stress concentration. Under different concentrations of Na2CO3 stress， the SOD activity generally showed an upward trend， reaching the maximum value at 50 mmol·L-1， and the contents of Chl， Chla， and Chlb generally showed a downward trend. However， under the same time conditions of stress， ρ（Chla）/ρ（Chlb） decreased first and then increased with the concentration increasing， and the ratio of ρ（Chla）/ρ（Chlb） was the smallest under 40 mmol·L-1 treatment. In general， ‘Silver Fan’ seedlings had a certain salt alkali resistance ability， and could grow at NaCl concentration<90 mmol·L-1， NaHCO3 concentration<60 mmol·L-1， and Na2CO3 concentration< 40 mmol·L-1， and had certain ornamental value， respectively. The results of principal component analysis showed that the relative conductivity， Chla， and Chlb contents could be used as indicators for evaluating the salt alkali resistance of the ‘Silver Fan’.
To explore the effect of tree age of ancient Platycladus orientalis on rooting of cuttings propagated from them and the physiological mechanism during the cutting process， the cuttings of 5， 100， 300 and 700 years P. orientalis female trees were used as scions respectively， and the phloem at the base of the cutting at rooting stages［0 d （S1， stage of before cutting）， 35 d（S2， stage of callus formation）， 65 d（S3， stage of adventitious root formation）， 95 d（S4， stage of adventitious root elongation）］ were harvested as the materials and the dynamic changes in the physiological indicators were measured， and the rooting rates and the numbers of rooted cuttings were counted respectively. The results showed that both of the rooting rates and the numbers of rooted cuttings propagated from ancient P. orientalis were significantly less than those of five years ones（P<0.05）. The nutrients（total sugar and total protein）， activities of antioxidative enzymes（polyphenol oxidase（PPO），peroxidase（POD）， superoxide dismutase（SOD）） and hormones（Indole-3-acetic acid（IAA）， zeatin riboside（ZR）） contents of the cuttings of five years donors were significantly more than those of ancient P. orientalis donors at all rooting stages， indicating that the high levels of these substances facilitated the rooting of the cuttings（P<0.05）. The contents of malondialdehyde（MDA）， abscisic acid（ABA）， and gibberellin（GA） showed a significant increase with increasing tree ages， indicating that the cuttings of ancient P. orientalis contained more harmful substances and hormones that inhibited rooting（P<0.05）. The nutrients（total sugar and total protein） and hormone（IAA and GA） contents showed a trend increased first and then decreased throughout the four stages， and it was worth noting that the contents reached maximum value at S3. On the contrary， ABA contents at S3 were significantly lower than that of another three stages（P<0.05）. The results indicated that the stage of adventitious root formation（S3） was a critical stage during the cutting process（P<0.05）. The larger the ratio of ω（IAA）/ω（ABA） and ω（ZR）/ω（ABA） were， the better for adventitious root formation. Tree ages significantly affected the rooting rate of P. orientalis cuttings， but there was no significant difference in the rooting rate of cuttings of ancient P. orientalis of different ages. Therefore， the reasons for difficulties in rooting of cuttings from ancient P. orientalis were mainly attributable to the lack of nutrients（total sugar and total protein）， activities of antioxidative enzymes（PPO， POD， and SOD） and endogenous hormones（IAA and ZR） beneficial to rooting.
