Dynamic response of plant diversity, community and interspecific association along environmental gradients is one of the basic issues in community ecology and biodiversity science. Soil salinity is one of the most decisive factors that govern desert plant community dynamics. The Ebinur Lake wetland national nature reserve is located in typical arid desert area. Previous related studies about the reserve had point out that soil salinity influences the desert plant community characteristic significantly, but the specific role of soil salinity in plant community dynamics is still unknown. Based on this, the objective of this study is focused on the responses of desert plant diversity, community overall association and interspecific association to soil salinity gradient.
In this study, altogether 74 sampling plots were investigated; including 22 plots for trees (10 m×10 m), 35 plots for shrubs (5 m×5 m) and 17 plots for herbs (1 m×1 m). At each plot, abundance, height and diameter at breast height of trees, abundance of shrubs and herbs were surveyed. According to soil salinity of the corresponding plot, all plots were classified to 3 salinity gradients by cluster analysis, with the salt contents of low (S1), middle (S2) and high (S3) defined as 0.03%-0.55% (S1), 0.61%-1.24% (S2) and 1.41%-1.79% (S3) respectively. A range of different diversity indices including Shannon-Wiener, Simpson, Pielou, Fisher-α of logarithmic series distribution and Margalef were calculated to examine the plant diversity under each salinity gradient. Variance ratio (VR), χ² test and Spearman rank correlation were employed to quantitatively analyze the community overall association and interspecific association under different salinity gradient. VR value, proportion of species pairs with positive and negative correlation, Dice index and Spearman rank correlation coefficient were used in exploring response of overall association and interspecific association to different soil salinity. The results indicated that: 42 species (which belong to 39 Genus of 18 Family) were identified in the Ebinur Lake wetland national nature reserve. Along the soil salinity gradient (S1-S3), (1) Life form structure in community was changed, more specifically, proportion of herbaceous decreased while tree proportion increased as salinity increases, and shrubs proportion decreased slightly. (2) Plant diversity indices decreased with increased soil salinity, and showed a very significant positive correlation in low salinity (P<0.01), then the correlation turned into partially significant negative (P<0.05) in middle salinity and showed positive mainly in high salinity gradient (P>0.05). (3) Community overall associations was significant positive in low (VR=1.42) and middle (VR=1.89) salinity, but converted to negative (VR=0.62) in high salinity, which means that high soil salinity lead to the decrease of community stability. (4) Along rising gradient of soil salinity, number of species pairs with a negative correlation increased, while number of species pairs with a positive correlation decreased; both of positive and negative correlation strength (coefficients) was enhanced as soil salinity increases; ratio of positive species pairs to negative species pairs showed a significantly positive correlation with diversity (P<0.05). In conclusion, reduced desert plant diversity and shifted community and interspecific association under high salinity threatened plant community stability of arid area, and may lead to retrogressive succession of community. Results of the present study provide a scientific basis for arid area in vegetation management, vegetation restoration and soil salinization prevention.