In order to answer the controversial question of the effects of Eucalyptus introduction on plant diversity， the Eucalyptus forest in Lancang County， a large-scale introduction area of Eucalyptus in Yunnan Province， was taken as the research object， and the secondary evergreen broad-leaved forest and artificial Pinus kesiya forest were used as reference forests， and six groups of comparative plots were set up， and the plants were divided into different functional groups. The species composition characteristics and species diversity index of each functional group under Eucalyptus forest and reference forest were compared and analyzed， and the effects of Eucalyptus introduction on the species composition and diversity of understory plant functional groups were examined. The results showed that： （1）the replacement of the secondary evergreen broad-leaved forest by Eucalyptus plantation would increase the number of species in the warm-sun-medium functional group and decrease the number of species in the warm-shade-wet functional group. The replacement of artificial Simao pine forest by Eucalyptus forest would increase the number of species in warm-shade-wet functional group and reduce the number of species in warm-sun-medium functional group. （2）the species composition and important value of understory plants changed after Eucalyptus forest replaced the two reference forests， Eupatorium adenophorum occupied the absolute dominant position of warm-sun-medium functional group， and Arthraxon hispidus occupied the absolute dominant position of warm-shade-wet functional group. （3）after Eucalyptus forest replaced the two reference forests， the Shannon-Wiener diversity index and Pielou uniformity index of the warm-sun-medium functional group under the forest were significantly decreased（P<0.05）， but there was no significant effect on the species diversity index of the warm-shade-wet functional group（P>0.05）. In conclusion， Eucalyptus introduction changed the species composition of understory plant functional groups， and had different effects on the species diversity of different plant functional groups.
To explore the mixing effect of Cunninghamia lanceolata and Elaeocarpus sylvestris， 20-year-old pure and mixed C. lanceolata and E. sylvestris plantations in Fengshushan Forestry Farm in Jingdezhen were selected as test objects， and three slope positions（up slope position， middle slope position and down slope position） were set for each stand type， and the effect of mixed tree species on the plantation growth was analyzed， and the responses of the mixed effects on site condition and on environmental factors was investigated， respectively. The results showed that the volume of the mixed forests ircreased by 5% compared with the expected volume， showing a slightl increase. Compared with pure stands， the diameter distributions of the two species showed opposite trends to the mixed， the peak of diameter distribution of C. lanceolata in mixed stands moved towards higher order， however， the peak of diameter distribution of E. sylvestris in mixed stands moved towards lower order. The allometric analysis of coarse root diameter-stem diameter of pure and mixed plantations showed that C. lanceolata allometry in mixed forests was focused on stem growth， while E. sylvestris allometry in mixed forests was focused on root growth， regardless of forest type and tree species， tree growth would focus on stem growth from slope position to bottom. There was a significant negative correlation between the mixed effect of C. lanceolata and E. sylvestris and the site index， the soil available phosphorus was the main limiting factor for the growth of the mixed forests. The mixed forest of C. lanceolata and E. sylvestris might improve stand growth， and the mixed stands had better adaptability to poor site conditions.
In this study， the soil enzyme activities， stoichiometric characteristics and major environmental factors of Sarcococca ruscifolia and Fargesia spathacea communities at different depths（0<h≤10 cm， 10 cm<h≤20 cm） were examined in the natural Fagus forest in Micang Mountain Nature Reserve， Sichuan. The results showed that： （1）In different understory plant communities， the total nitrogen（TN） content in plantless community was higher than that in plant community soil. At the soil depth of 10 cm<h≤20 cm， the contents of total carbon（TC） and soil available nitrogen（SAN） were the highest in the S. ruscifolia community. （2）The soil enzyme activities （acid phosphatase（AP）， 1， 4-β-N-acetylglucosaminidase（NAG）） in the S. ruscifolia community were significantly higher than those in the no plant community and the F. spathacea community， and the activities of β-glucosidase（BG） and leucine aminopeptidase（LAP） were the highest in the F. spathacea community. The activities of polyphenol oxidase（PPO） and peroxidase （POD） in plant community were significantly higher than those in no plant community. （3）Soil enzyme activities of BG， LAP， PPO and POD were significantly positively correlated with soil pH， and soil enzyme activities（except cellobiohydrolase（CBH）） were significantly positively correlated with soil moisture content. The results of redundancy analysis（RDA） showed that soil moisture content， SAN and TC content explained 51.4%， 40.5% and 37.7% of the variation of soil enzyme activity and its stoichiometric characteristics， respectively. （4）The vector angle（VA） was greater than 45°， suggesting that soil microorganisms were more susceptible to phosphorus restriction. The results indicated that different understory plant communities could affect soil physical and chemical properties and soil enzyme activities and their stoichiometric characteristics were mainly regulated by soil moisture content， SAN and TC content.
Exploring the characteristics and its driving forces of plant community in different geomorphic units in arid gravel desert areas was of great significance for the development of targeted natural plant community protection measures， and the construction of reasonable artificial restoration plant communities in different geomorphic units in arid region. In this paper， the plant community composition and diversity in four micro-geomorphic units（gravel desert Gobi， wind erosion unaka， aeolian sandy land and valley land） were analyzed， and the main ecological factors affecting plant community characteristics in different geomorphic units were explored based on the monitoring of soil and micro-meteorological factors. The results showed that： （1）Plant community in gravel desert areas was distributed in patches， with one to two layers vertical structure， and the life forms were mainly annual plants and small shrubs. About 45% shrubs were found in arid gravel desert Gobi， while about 50% species were annual plants in wind erosion unaka and aeolian sandy land. The plant community in the valley land contained all five life forms， including a few trees and vines. （2）The plant community coverage， plant density， diversity and stability were the highest in valley among four micro-geomorphic units， followed by wind erosion unaka. The plant community diversity and stability were lowest in gravel desert Gobi with the plant sparsely distributed and the aeolian sandy land with simple community structure. （3）Soil moisture content， organic matter， soluble salts and surface temperature were the main same factors affecting plant diversity， productivity and community stability in arid gravel desert areas. In addition， the soil bulk density in wind erosion unaka， the surface wind speed in arid gravel desert Gobi and aeolian sandy land were also the factors affecting plant community characteristics in different micro-geomorphic units. In summary， different vegetation restoration measures should be formulated after ecological disturbance in arid gravel desert on the basis of the main ecological factors affecting plant communities in different geomorphic units， such as reducing surface temperature in gravel desert Gobi， restoring constructive species by improving soil quality in wind erosion unaka and aeolian sandy land， and maintaining ecological water using in valley land.
Apocynum venetum is an important wild germplasm resource in China， and understanding the characteristics of A. venetum community and its relationship with environmental factors is of great significance for the protection and rational development and utilization of A. venetum germplasm resources. The wild A. venetum distributed in Jinta County， Minqin County， Hangjinqi， Zhaluteqi， and Baicheng City were used as materials. Based on the community composition and habitat characteristics， the biodiversity and its relationship with climate factors， and environmental factors affecting the changes in A. venetum communities were analyzed respectively. The results showed that： the species diversity of the five plots from high to low was Zhaluteqi， Minqin County， Baicheng City， Jinta County， Hangjinqi， with Zhaluteqi having the highest biodiversity（H=2.591， D=2.511， E=0.796， R1=44.833， R2=6.423）， and Hangjinqi had the lowest biodiversity（H=1.173， D=0.915， E=0.564， R1=3.641， R2=1.968）. The species diversity of A. venetum community was closely related to precipitation， temperature and evaporation， especially the Gleason and Margalef index were significantly positively correlated with precipitation in May， June and July， indicating that precipitation during the growing season was important to community species diversity.
