西藏横断山区溪流细菌beta多样性组分对气候和水体环境的响应

理解沿环境或空间梯度的群落组成变化(即beta多样性)一直是生态学和保护生物学的中心问题, 且beta多样性的形成机制及其对环境的响应已成为当前生物多样性研究的热点问题。本文以西藏横断山区怒江和澜沧江两个流域入江溪流中的细菌为研究对象, 使用Baselga的beta多样性分解方法, 基于Sørensen相异性指数将细菌的beta多样性分解为周转(turnover)和嵌套(nestedness)两个组分, 探究了细菌beta多样性及其分解组分随海拔距离的分布模式, 并且衡量了环境、气候和空间因子的相对重要性。结果表明, 两个流域中细菌的群落结构显著不同。两个流域的细菌总beta多样性和周转组分随海拔距离的增加而增加, 周转组分占总beta多样性的比例较大。气候和环境因子是两个流域中细菌总beta多样性及周转过程的重要预测因子, 并且所有的显著因子均为正相关, 其中环境因子中相关性最高的为海拔距离(R ²= 0.408, P < 0.001), 而气候因子中相关性最高的为年均温差(R ²= 0.417, P < 0.001)。方差分解结果暗示嵌套组分主要受空间扩散的影响; 总beta多样性和周转组分在环境较恶劣的澜沧江主要受环境过滤的影响, 而在环境较温和的怒江主要受空间扩散和环境过滤的共同影响。此外, 较为恶劣的环境条件会增加细菌的总beta多样性和周转率, 并且会形成更强的环境筛选作用去影响细菌群落的物种组成。我们的研究表明对西藏横断山区水体细菌多样性的保护需要从整个流域入手, 而非少量的生物多样性热点地区。

Beta diversity of stream bacteria in Hengduan Mountains: The effects of climatic and environmental variables

Understanding community composition variation (beta-diversity) along environmental and spatial gradients is a central interest in ecology and conservation biology. Although bacterial elevational patterns are somewhat established, their underlying processes were understudied. To better understand the patterns behind beta diversity, we investigated aquatic bacterial community composition in individual streams in Nujiang and Lancang rivers located in the Hengduan Mountains of the Tibetan Plateau. Using Baselga’s approach of beta diversity partitioning based on the Sørensen dissimilarity index, we explored the elevational patterns of turnover and nestedness through linear models and measured the relative importance of environmental, climatic, and spatial factors on bacterial beta diversity with multiple regression on distance matrices and variation partitioning analyses. Our results showed bacterial community composition differed between the Lancang and Nujiang rivers. Total beta diversity and turnover component increased with increasing elevational distance, and total beta diversity was driven by turnover component. Climatic and environmental factors were important predictors of total beta diversity and turnover component in the two catchments, and all the significant correlations were positive. The highest correlation factors were elevation distance (R ² = 0.408, P < 0.001) and mean annual temperature (R ² = 0.417, P < 0.001). The variation partitioning results suggest nestedness component was heavily affected by dispersal limitation while total beta diversity and turnover were mainly affected by environmental filtering. Moreover, harsher climate conditions will increase total beta diversity and turnover, and form stronger environmental filtering processes that impact the bacterial species composition. Our research shows that the conservation of bacterial diversity in the stream of Hengduan Mountains in Tibet needs to target the whole multiple sites, rather than a few richest sites of biodiversity.