Response Of Plant Diversity To Aridity And Salinity Stress In Ebinur Lake Basin

One of the key hypothesized drivers of community assembly and dynamics is environmental filtering,where environmental stress limits species migration and survival as a result of functional trait convergence.Whereas most such studies focus on large-scale variation in functional traits along a single-factor environmental gradient,the mutual effects of small-scale multiple environmental filtering remain unclear.Furthermore,it has rarely been tested whether the combined effect of aridity and salinity on local dryland vegetation constrains the patterns of species richness,functional traits and phylogenetic structures.Soil moisture and salt play key roles in regulating desert plant nutrient cycles on a local scale.However,information on the response of plant nutrient stoichiometric patterns to soil water and salt gradients and biodiversity is limited.Here,we assessed leaf N and P levels of 18 species of desert plants and measured the corresponding soil nutrient,water and salt concentrations,at four dry sites,five humid-saline sites and four humid-non-saline sites?reference sites?along a transect in a temperate desert in Xinjiang Province,northwest China.Across an 8-km long transect in the arid northwest of China,the distribution pattern and adaptive mechanism of alpha diversity and beta diversity were revealed in water and salt gradient,the adaptation of N:P stoichiometry to drought and salt stress was clarified,and the relationship between N:P stoichiometry and species diversity was further clarified.We assessed the role of environmental filtering in shaping community assemblages by testing the hypotheses that aridity and salinity stresses,interspecific competition and phylogenetic structures constrained functional diversity in the local dryland vegetation.?1?In the vertical gradient,soil moisture content and salt content increased gradually from top to bottom.The average soil moisture content was 20.66%and the minimum was 0.20%.The average salt content was 70.57 g kg^-1,and the maximum was197.87 g kg^-1.The average pH value of the 13 samples ranged from 7.96 to 9.14.The difference of soil nutrients was not significant between the sample sites except site 8.Soil organic carbon,total nitrogen and total phosphorus were within the range of1.16-4.02 g kg^-1,0.19-0.34 mg g^-1 and 0.25-0.31 mg g^-1,respectively.Soil organic carbon content and soil total nitrogen content increased significantly with the increase of soil water content and soil salt content,respectively.On the contrary,soil total phosphorus content decreased linearly with the increase of soil water and salt content,respectively.The increase of soil moisture content significantly reduced soil pH value.With the increase of soil salinity,soil pH value first increased rapidly and then stabilized around 9.2.The water-salt coupling phenomenon is obvious in the study area.When the soil moisture content increases by 1.00%,the salt content will increase by 0.12%.Soil nutrients also presented a coupling mechanism,and soil total nitrogen,soil total phosphorus and organic carbon content showed a tendency to grow together.Soil organic carbon and soil total phosphorus also showed a tendency to increase together,but it was not significant.?2?Simpson index,Shannon-wiener index and Margalef index in dry-non-saline sites were significantly lower than those of the other two habitats.Shannon-wiener index of humid-salt habitats was significantly lower than those of the other two habitats.The Pielou index of the three habitats showed no significant difference.On the local scale,water and salt participate in the filtering process of community species composition,but niche differentiation plays little role.Both drought and salt stress significantly reduced the community diversity of the desert ecosystem,but drought stress was more obvious.Soil pH value significantly decreased the community alpha diversity.Soil nutrients had no significant effect on the alpha diversity.Shannon-wiener index and Margalef index were more sensitive to the response of alpha diversity to environmental factors.It was found that the beta diversity in dry-non-saline habitats was significantly lower than those of the other two habitats.On the contrary,the similarity indexes in dry-non-saline habitats habitats were significantly higher than those of other habitats.The diversity index and similarity index of in wet and high salt habitats were lower than those in wet and no salt habitats,and the difference was not significant.The higher the degree of drought,the lower the beta diversity,and the lower the replacement rate of species.Increases in soil pH reduced the beta diversity,but not significantly.The similarity index had significant negative linear correlation with soil moisture,salt and total nitrogen content.The community species richness,soil moisture and salinity increased exponentially to the maximum value.SES.C-score index has significant negative linear correlation with soil salinity and pH value.Soil nutrients and pH values had no significant effect on species richness.SES.C-score was more sensitive to show the influence of environmental filtering on community construction.?3?Compared with the stoichiometry of the leaves at the humid-non-saline sites,the content of nitrogen and phosphorus in the leaves of the desert plants at the dry-non-saline and the humid-saline sites was lower,and the quality of nitrogen and phosphorus was higher.Different from the driving effect of salinity on N concentration plasticity of species,drought and salinity have an interactive effect on the plasticity of P and N:P ratio.The N,P concentrations and N:P ratios of plant communities were positively correlated with shallow and deep soil moisture,respectively.Moreover,drought reduced the plasticity of N content and increased the plasticity of P content in the plant community.High N and P concentrations in plant communities can maintain high species diversity.On the contrary,the lower N:P value of plant community leaves can better reflect the higher species diversity.Plants in the community maintain high species diversity by increasing the plasticity of N concentration.The lower plasticity of P concentration and N:P value in leaves of plant community is conducive to the maintenance of higher species diversity.In summary,the stoichiometry of plant communities showed a consistent trend in maintaining the alpha and beta diversity,respectively.?4?In this study,we used a unique method to separate the effects of drought and salinity in explaining the differences and convergent patterns of functional characters and lineages of local spatial scale communities.The results showed that drought significantly improved the convergence of plant height,specific leaf area,leaf area and leaf nitrogen concentration.However,salinity significantly promoted the convergence of leaf area and leaf nitrogen concentration.Similarly,interspecific competition increased the convergence of plant height and leaf area.Leaf area significantly converges due to phylogenetic history.The effect of drought on the phylogenetic structure of desert plants is greater than that of salinity.Drought filtered to the aggregation of NRI index,while salt filtering had no obvious effect.Further study showed that drought filtering had a negative effect on NTI,but salt filtering had a positive effect on NTI.The effects of interspecific competition and phylogenic structure on the functional diversity of desert plants were weak.The results of structural equation model show that drought has a significant direct negative effect on functional diversity and species richness.Salt,phylogenic diversity and species richness had direct negative effects on functional diversity.Drought has direct positive effect on phylogenic diversity.It has indirect positive effect on functional diversity.To sum up,drought and salinity both play important roles in the filtering of desert plant community assembly?drought plays a more important role in the filtering?,which reduces the diversity of alpha and beta in the community,leading to the convergence of species'functional shapes and the aggregation of family tree structure.Historical evolution factors had obvious convergent influence on the functional shapes of some communities?such as leaf area?.Niche differentiation only resulted in obvious character differentiation of maximum plant height.