To complement and improve the community composition and structural characteristics of the summit mossy dwarf forests in Southwest China， based on the community survey data of the 1 hm2 forest dynamic plot（FDP）， the Center for Tropic Forest Sciences（CTFS） standard was used to investigate all woody trees with DBH ≥ 1 cm in the plot. Then， ten standard plots（a total of 0.6 hm2， 20 m×30 m each） were selected from the 1 hm2 FDP， and all vascular plants within the 0.6 hm2 plot were investigated and counted by plant community inventory. The species composition and community structure were analyzed by the aspects of species richness and quantitative characters， and the diameter class structure of the dominant tree species. The main results were as follows： （1）there were 3 614 woody individuals from 42 species， 32 genera， 20 families， with DBH≥1 cm within the 1 hm2 FDP； in the 0.6 hm2 plot， there were 103 species of vascular plants in 42 families， 67 genera and 1 536 individuals of 24 woody species with height≥3 m； （2）Rhododendron sinofalconeri was， absolutely dominant in the community， with important values 3-4 times higher than those of the secondary dominant species； （3）The age structure of the whole community showed a “L” shape； however， Rhododendron sinofalconeri was dominant in adult individuals， being different from other dominant species； （4）The community was composed of tree， shrub and herb layers as well as epiphytes and parasitic plants， and named as Rhododendron sinofalconeri， Clethra delavayi var. yuiana， Illicium tsaii summit mossy dwarf forests. In the Bozhu Mountain， Wenshan county， Yunnan， China， the mossy dwarf forest community was rich in species， stable in composition， prominent in dominant species and good in their regeneration. The canopy appearance of the community was flat， and the community succession was in a mature forest state.
Seeds of 18 F. mandshurica clones were used as materials， the germination performances of clones at suitable temperatures after different stratification treatments were compared， and the relationships between germination performances and seed embryo growth changes were analyzed. The results showed that the germination performances of seeds were different among F. mandshurica clones after different stratification treatments. Seed dormancy of clones 1， 2 and 6 was shallow and could be broken after variable temperature stratification treatments for a short time（a total 18 weeks）， which the germination rate of clones 2 and 6 reached more than 75%. Seed dormancy of clones 13， 14， 15 and 16 were broken by 20-week stratification treatment （cold temperature extended for two weeks）， and clones 4， 8， 11 and 12 by 20-week stratification treatment （warm temperature extended for two weeks）. Seeds dormancy of clones 5 and 18 was deep-degree， it could be broken by extending the stratification（warm and cold temperature） time to 22 weeks. Seed dormancy of clones 3， 7， 9， 10 and 17 could be broken by stratification treatment for 20 weeks， without significant difference in the dormancy between seeds treated by extending warm and cold stratification time. The changes of embryo length， embryo rate and embryo mass ratio in the process of stratification were different in different clones， and relative extension time（two weeks） of cold temperature stratification in clones 6， 7 and 11 was conducive to embryo growth， and extension time（two weeks） of warm temperature stratification in clones 2， 5 and 17 was conducive to embryo growth. Differences in seed dormancy of different clones could not be accurately judged by changes in seed embryo growth during the stratification process， which should be judged mainly by the germination performances. The results could provide a reference for the selection of mother clones with shallow seed dormancy in production practice.
To address the problem of the rooting ability of Fraxinus mandshurica cuttings significantly decreasing after three years due to age effect， four-year-old F. mandshurica seedlings were used to investigate the role of cycle rejuvenation through cuttings in overcoming age effect in this study. The impact of the number of cycles and topping treatment on the sprouting， growth， and rooting of F. mandshurica cuttings， as well as the physiological changes during its rejuvenation process were examined. The results showed that the measurement of increasing the number of rejuvenation cycles and topping treatment both enhanced the degree of rejuvenation in F. mandshurica， which were characterized by an increased number of sprouted branches， finer branches， and shorter internodes， while significantly improved the regeneration ability of the cuttings. When the number of rejuvenation cycles reached three and was combined with topping treatment， the number of sprouted branches increased by 6.56 times， and the rooting rate increased by 7.44 times compared to non-rejuvenated treatment. During one to three rejuvenation cycles， the indole acetic acid（IAA） and cytokinin（CTK） levels in the plants increased， the gibberellin（GA3） levels significantly increased only at the third cycle， and the abscisic acid （ABA） levels decreased gradually. After rejuvenation， the activities of catalase（CAT）， peroxidase（POD）， and superoxide dismutase（SOD） and the contents of malondialdehyde（MDA） and soluble sugars decreased in the regenerated plants. These physiological changes were consistent with the juvenile state of the plants. Cycle rejuvenation can effectively restore the juvenile state， induce the formation of sprouts with higher IAA and GA3 levels and lower ABA levels， and simultaneously reduce the oxidative state and soluble sugar content in F. mandshurica. These changes are beneficial for achieving rejuvenation of F. mandshurica， thereby increasing the rooting rate of F. mandshurica cuttings and enabling rapid and efficient clonal propagation of superior F. mandshurica varieties.
Exploring the coupling relationship among stand structure， site conditions， protection intensity， and plant diversity is helpful to improve the effect of plant diversity protection in protected areas. Based on this， the forest community of the Chuona River National Nature Reserve in Daxing’anling Mts was selected as the research object， the plant diversity and stand structure characteristics of the arbor， shrub， and herb layers were investigated， and the soil samples were collected and the soil physicochemical properties were determined. The frequency distribution， redundancy ranking and variance analysis were used to reveal the characteristics of plant diversity and its coupling relationship with influencing factors. The results showed that：（1）Larix gmelinii was the dominant tree species in the tree layer of Chuona River Reserve， with a relative abundance of 64.35%， followed by Betula platyphylla. The proportion of lingonberry（Vaccinium vitis-idaea） in shrubs was the highest， reaching 72.70%. A total of 77 herbs were recorded， of which Carex callitrichos accounted for the largest proportion（23.72%）. （2）The order of richness index and diversity index was herb layer>arbor layer>shrub layer， and the shrub layer had the highest evenness index. （3）Redundancy analysis and variance decomposition analysis showed that the independent effects of stand structure explained the most changes in plant diversity. Herbaceous coverage， shrub density， tree height and soil bulk density were most closely related to plant diversity changes. Adjusting stand structure would be a simple and reliable way to improve plant diversity， and the above results provided data support for stand management in Daxing’anling Mts.
The fixed monitoring plot was conducted in the Xilinhe National Nature Reserve to analyze tree species diversity， dominant species niche， interspecific associations and community stability in the Piceakoraiensis-Abies nephrolepis-Pinus koraiensis forest community by using a series of analysis methods including the α diversity index， the niche determination， the variance ratio（VR）， the Chi-square test（χ2 test）， the Spearman’s rank correlation coefficient test and the M. Godron stability. The results showed that： （1）the plot encompassed 20 tree species， 14 families and 14 genera， with a balanced distribution of trees， and the α diversity index was high； （2）the community niche overlap index was relatively high， but the cases with large （>0.7） or small（<0.4） niche overlap index were rare with a moderate degree of niche differentiation； （3）the overall correlation of the community was nonsignificant positive， and the interspecific correlations among the main tree species were mainly positive and nonsignificant correlation with strong interspecific independence； （4）the stability of M. Godron analysis fell to the point（32.79， 67.21） and was far from the stable point （20， 80）， indicating poor community stability； （5）P. koraiensis had the highest importance value and niche width in the sample plot， the average niche overlap index with other tree species was higher than the average value of the sample plot； the species was dominated by large-diameter individuals， and the relative frequency among tree species was low. Therefore， during the restoration process of Piceakoraiensis-Abies nephrolepis-Pinus koraiensis forest， the appropriate artificial intervention should be carried out to promote the recovery of Pinus koraiensis population， to regulate interspecies relationships， to enhance interspecies association strength， and to strengthen monitoring and protection of rare plant populations when community stability declined.
In order to reveal the mechanism of selenium alleviating the cadmium stress in Astragalus membranaceus， the traditional medicinal plant A. membranaceus was used as materials， and the roles of ion antagonism， antioxidant enzyme system， heavy metal chelates and isoflavones in alleviating the Cd stress by Se were clarified comprehensively using hydroponic cultivation method. The results showed that 10 μmol·L-1 Se significantly improved the growth of A. membranaceus seedlings under 50 μmol·L-1 Cd stress， and reduced the accumulation of reactive oxygen species and membrane lipid peroxidation levels. The addition of Se significantly reduced the Cd content in all parts of A. membranaceus under Cd treatment. Meanwhile， the addition of Cd also reduced the Se content， indicating that it has a significant antagonistic effect on the absorption of Se and Cd. Se reduced the activities of POD， SOD， APX， CAT and GR in all parts of A. membranaceus under Cd stress. Correlation analysis showed that various antioxidant enzymes activities were significantly positively correlated with O2•- content， suggesting that the changes of antioxidant enzyme activity were more adapted to the level of reactive oxygen species in the plants. In addition， the addition of Se also reduced the content of non-protein sulfhydryl groups and metallothionein in all parts of A. membranaceus exposed to Cd treatment， and the contents showed a good positive correlation with the Cd content in corresponding part， indicating that the content of heavy metal chelates was regulated by the Cd content in various parts. Unlike antioxidant enzymes and metallothionein， the contents of three isoflavone components were significantly increased by Se addition in the roots of A. membranaceus seedlings under Cd stress. Furthermore， the expression levels of key enzyme genes in the isoflavone synthesis pathway， including CHS， IFS， I3'H， IOMT and UCGT， were significantly upregulated by Se under Cd stress. In summary， Se decreased the content of Cd in A. membranaceus seedlings under Cd treatment by antagonizing Cd during the absorption process， and reduced the degree of plant stress. At the same time， Se improved the tolerance of plant to Cd stress by upregulating the synthesis of secondary metabolites such as isoflavones.
To investigate the dormancy type and physiological and metabolic characteristics of Acanthopanax senticosus seeds during germination， the seeds from northeast China were treated with sand accumulation for 140 days under different temperature conditions（20 ℃， 4 ℃， 20 ℃/4 ℃） respectively. Five distinct stages were identified based on embryo phenotypic changes，and the dynamic changes in endogenous hormones， main nutrient substances and their hydrolases， antioxidant system， and metabolomics during these five stages were examined respectively. The results revealed that： （1）A. senticosus seeds exhibited good water absorption； while the constant temperature of 20 ℃ only promoted embryo elongation， but not germination. There was no increase in embryo rate at 4 ℃， and the embryo rate increased and the seeds germinated only when the temperature was maintained at 20 ℃ for 0-110 d and 4 ℃ for 110-140 d. （2）As the embryo growth rate increased， gibberellic acid content increased while abscisic acid content decreased. The levels of indoleacetic acid， indolebutyric acid， and naphthenic acetic acid all decreased. Fat content decreased while soluble sugar content increased. Fat content showed a significant negative correlation with lipohydrolase activity as well as a highly significant negative correlation with soluble sugar content. （3）A total of 92 differential metabolites were screened， and the carbon metabolism， energy metabolism， and antioxidant metabolism were the major differential metabolic pathways. Additionally， there were difference in sesquiterpene and triterpene biosynthesis， fatty acid biosynthesis and glyceride metabolism. In conclusion， seeds of A. senticosus were morphological and physiological dormancy， and variable temperature stratification was a necessary condition to break seed dormancy， and endogenous hormones might regulate seed dormancy and germination. Macromolecular nutrients such as fat were decomposed by hydrolases to provide material and energy for seed germination， which was also one of the necessary conditions for seed germination. This study provided theoretical guidance for identifying seed dormancy types and artificial propagation of A. senticosus.
Based on the fact that soil microorganisms can enhance the adaptability of plants to global change， the effects of soil microorganisms on the ecological stoichiometric characteristics of rhizosphere soil microorganisms were studied under the background of nitrogen deposition， and then the regulation of changes in ecological stoichiometric characteristics on the soil microbial nutrient limitation was explored. Under the premise of soil sterilization treatment（sterilized soil（+S） and non-sterilized soil（-S））， one-year-old potted seedlings of Caragana korshinskii were inoculated in two ways（inoculation（+M） and without inoculation（-M））， and nitrogen addition treatments（no nitrogen application（CK）， low nitrogen（LN， 3 g·m-2·a-1）， high nitrogen（HN， 6 g·m-2·a-1）） were set up. Compared with the original microbial community composition in non-sterilized soil without fungus inoculation， the correlation between ecological stoichiometric characteristics of microhabitat and microbial nutrient limitation under different treatments was explored.Results were as follows： （1）In sterilized soil treatment， the relative abundance of fungi in the rhizosphere soil of C. korshinskii mycorrhizal seedlings was significantly increased by 82.20%， 25.00% and 59.84% under CK， LN and HN treatments than that of non-mycorrhizal seedlings， respectively. （2）In the treatment of non-sterilized soil， the microbial biomass carbon-to-phosphorus ratio in the rhizosphere soil of non-mycorrhizal C. korshinskii seedlings under LN treatment was lower by 46.28% compared to CK treatment（P<0.05）， while that of mycorrhizal seedlings was 56.76% higher compared to CK treatment（P<0.05）. （3）Under the nitrogen addition treatments， stoichiometry of carbon and nitrogen-related soil enzyme activity， stoichiometry of carbon and phosphorus-related soil enzyme activity， and vector length in the rhizosphere soil of C. korshinskii non-mycorrhizal seedlings under sterilized soil treatment were significantly lower than those of mycorrhizal seedlings（P<0.05）. （4）PLS-PM path analysis showed that the total effect coefficient of microbial regulation on microbial nutrient limitation was greater than that of nitrogen addition treatment. In summary， soil indigenous microorganisms and mycorrhizal fungi synergistically regulated the enzymatic stoichiometric ratio of rhizosphere soil， and enhanced the adaptation of soil microbial nutrient limitation to nitrogen addition.
To provide a theoretical basis for the timely harvesting of Aralia elata， the cultivated A.elata was used as experimental materials， and the biomass， photosynthetic pigment content， total phenolic content， total flavonoid content， and antioxidant capacity of A. elata leaves in different harvesting periods（S1 period， April 10th， 2023； S2 period， April 30th， 2023； S3 period， May 20th， 2023； S4 period， June 9th， 2023） were analyzed respectively. Meanwhile， the high-performance liquid chromatographic（HPLC） method was established to determine the contents of araloside X， araloside V， and araloside A. Based on high-performance liquid chromatography-mass spectrometry metabolomics technology， the differences in secondary metabolites of A. elata at different harvesting periods were compared and analyzed. The results showed that： （1）The fresh weight， dry weight， and photosynthetic pigment content of A. elata leaves increased with growth， and reached the maximum value in the S4 period. （2）The contents of total phenol and total flavone reached the maximum value in the S1 period（1.36 mg·g-1， 29.38 mg·g-1）. （3）The scavenging ability of DPPH radical was the strongest in the S1 period（IC50 of 0.262 g·L-1） and the scavenging ability of ABTS radical was the strongest in the S2 period （IC50 of 0.511 g·L-1）. （4）The content of araloside A reached a maximum of 12.90 mg·g-1 in the S4 period. The contents of araloside V and X in the S2 period were significantly higher than those in other periods， which were 1.53 and 3.30 mg·g-1 respectively. （5）A total of 24 phenolic metabolites were identified， and the total amount of phenolic compounds in the four periods were 64.84， 119.31， 101.95 and 89.32 mg·g-1， respectively. Among the total phenolic compounds， the C6C1 backbone compounds （protocatechuic acid and gentisic acid）， the C6C3C6 backbone compounds （rutin）， and the C6C3 backbone compounds （caffeic acid） were significantly accumulated in the S2 period. In conclusion， considering the content of functional components， antioxidant activity， and edibility， the S2 period is the most suitable time for harvesting.
The establishment of shelter forests in the northeastern region of Ulan Buh Desert is a crucial ecological barrier to protect agricultural productivity within the eastern Hetao Plain. However， the lack of attention towards scientific research on artificial afforestation has resulted in a decline tendency in many shelter forest systems. The investigation of ecological adaptability of indigenous tree species after artificial cultivation was a crucial approach to guide the establishment and sustainable management of plantations. In order to further investigate the ecological adaptability of native tree species in Ulan Buh Desert after artificial cultivation， three native tree species： Ammopiptathus mongolicus， Zygophyllum xanthoxylon and Prunus mongolica were used as materials. By measuring the epidermal morphology， anatomical structure， and physiological indices of functional leaves， in conjunction with local meteorological data， the adaptive mechanisms of these plants to arid desert environments were clarified. The results showed that each of three plants exhibited distinct adaptations to arid desert environment in different ways. A. mongolicus enhanced light exposure and photosynthetic efficiency by augmenting leaf area， strengthened leaf mechanical defenses through dense epidermal hairs and well-developed cuticle， reduced light-induced damage and water transpiration， and maintained cellular water balance to minimize lipid peroxidation. The leaves of P. mongolica were clustered， by increasing number of leaves， the light receiving area was increased and the photosynthetic efficiency was improved， and by curling the leaves to avoid strong light burns， the water transpiration was reduced and the cell water balance was maintained by specializing the stomatal position（all the stomata were distributed on the lower surface of the leaves）， developed vascular bundles and rich mucous cells and crystal structures， and reduced cell membrane lipid peroxidation. The leaves of Z. xanthoxylon showed a cylindrical strip structure. By reducing the wind resistance， the probability of wind-sand flow damage to the leaves was reduced. The antioxidant enzyme activity and osmotic adjustment substance content in leaves was enhanced by physiological metabolic regulation， and the balance of cell water and reactive oxygen species metabolism was maintained. These findings suggested the different adaptation strategies adopted by the three plants in response to the desert environment， and provided the new ideas for introduction and domestication of native tree species in the northeastern Ulan Buh Desert.
