The decline of landscape connectivity caused by the increasing global habitat fragmentation has seriously threatened biodiversity. However, our understanding of how landscape connectivity affects biodiversity, especially for plant diversity, is limited. Taking the meadow of Poyang Lake as a case, this study firstly applied the landscape pattern metrics and the graph-theoretic connectivity metrics to analyze the changes of meadow structural connectivity and functional connectivity after determining the spatial distribution of meadow at each water level. Then, the impacts of meadow connectivity on plant diversity and its scale effects were revealed through the linear regression model (LRM), and the redundancy analysis (RDA) was used to explore the contrasted explanatory of meadow structural connectivity and functional connectivity to plant diversity patterns. The results showed that: (1) Meadow was submerged and divided by water and its shrinkage coexisted with fragmentation when the water level rose. While meadow emerged and spliced and its expansion co-occurred with cohesion when the water level fell. (2) When the water level increased, the shape of patch simplified, the area of patch shrank, the density of patch reduced, the aggregation of patch decreased and the meadow structural connectivity decreased progressively. Meanwhile, the number of components rose, the possibility of connectivity decreased and the meadow functional connectivity reduced dramatically. (3) Higher meadow connectivity not only led to greater plant species richness at the landscape scale but also increased plant community similarity at the patch scale. Functional connectivity explains plant diversity patterns better than structural connectivity. This thesis proposes a new insight of landscape connectivity for sustainable biodiversity conservation and landscape pattern optimization in lake areas.

Analyzing the dynamics of landscape connectivity is of great significance for biodiversity conservation, but the description of multiple ecological processes and the depth of coupling requires to be strengthen. Taking the grassland of Poyang Lake as a case, based on the integrated perspective of habitat and biology, comprehensively considering the ecological process of water level change and species diffusion, this study firstly analyzed the changes of landscape connectivity of grassland with different water levels and diffusion distances by using the graph-based connectivity indices. then, landscape pattern indices were applied to analyze the dynamics of landscape pattern of grassland and further study the effects of landscape pattern on connectivity. The results showed as follows: (1) From the perspective of habitat, grassland connectivity showed a sharp decrease with the increase of water level. From the perspective of ecology, the species diffusion distance had an absolutely positive impact on landscape connectivity. With the increase of diffusion distance, grassland connectivity increased significantly. (2) The dynamics of landscape pattern of grassland showed that with the increase of water level, the patch area shrank, the patch shape tended to be simple, the patch density decreased and the patch fragmentation aggravated. (3) The correlation results between landscape pattern and connectivity indicated that F had a significant positive relationship with PD, ED, PC had a strong significant positive relationship with LPI, COHESION, and NC had a negative relationship with LPI, ED, COHESION. This study provides theoretical guidance for the conservation and management of grassland in Poyang Lake.