Abstract:

Altitude has an important impact on spatial patterns of organisms. Exploring how biomes change with altitude can determine the geographic range of organisms. And it can predict how organisms will respond to climatic change. There were numerous studies on altitudinal patterns of biodiversity. However, most studies focused on macro-organisms with less consideration of micro-organisms which were seemed as “everything is everywhere, but the environment selects”. It is still unclear whether micro-organisms also display large-scale patterns as that of macro-organisms. In the present study, based on the survey data of Heiqu and Xuequ, two tributaries of the upper Jinsha River located in Changdu, Tibet, we analyzed altitudinal patterns and driving mechanisms of density, biomass, species richness, evenness and LCBD of benthic algae by generalized linear mixed models and piecewise structural equation models. A total of 161 taxa were identified, belonging to the Bacillariophyta, Cyanophyta and Chlorophyta. Diatoms (78.9%) are the most common phylum, with Achnanthidium minutissimum (28.3%), Reimeria sinuate (11.5%), Encyonema ventricosum (9.3%) and Nitzschia dissipata (7.2%) the dominant species. The composition of bethic algal communities in high-altitude areas was significantly different from that in low-altitude areas. Density, biomass, richness and local contribution to beta diversity (LCBD) of benthic algae showed evident altitudinal patterns, while evenness did not. Species richness decreased monotonically, while density, biomass and LCBD increased monotonically along the altitudinal gradient. Altitude had a significant effect on annual mean temperature, annual precipitation, solar radiation, electrical conductivity, dissolved oxygen, turbidity and flow velocity. Altitude affected local environmental variables by determining regional climate variables including average annual temperature, annual precipitation and solar radiation. Local environmental variables had direct influences on altitudinal patterns of benthic algae. Conductivity, dissolved oxygen and turbidity are the key drivers affecting altitudinal patterns of benthic algal communities. Our finding elucidates evident altitudinal patterns of benthic algal diversity, which provides important information on algal responses to climate changes. And it provides a scientific basis for the protection of biodiversity.

Key words: benthic algae, density, biomass, species richness, evenness, LCBD, altitudinal patterns

摘要：

海拔对生物群落的空间格局具有重要影响。探究生物群落随海拔变化规律不仅可以确定生物的地理分布范围，而且可为预测生物响应气候变化提供基础信息。然而，目前对于生物群落海拔格局的研究多集中于陆生大型生物，对水生微型生物的研究相对不足。基于西藏昌都市境内金沙江上游支流黑曲和雪曲着生藻类的调查数据，运用广义线性混合模型和分段结构方程模型探究着生藻类密度、生物量、物种丰富度、均匀度和样点对β多样性的贡献（Local contribution to beta diversity，LCBD）等生物群落指标的海拔格局及其驱动机制。结果表明：两条河流共鉴定出161个分类单元，分属硅藻门、蓝藻门和绿藻门。其中着生硅藻种类最多，占总分类单元数的78.9%，极小曲丝藻（Achnanthidium minutissimum，平均相对丰度：28.3%）、波状瑞氏藻（Reimeria sinuata，平均相对丰度：11.5%）、偏肿内丝藻（Encyonema ventricosum，平均相对丰度：9.3%）和细端菱形藻（Nitzschia dissipata，平均相对丰度：7.2%）为主要优势种。不同海拔的着生藻类群落组成存在显著差异。着生藻类物种丰富度随海拔梯度单调递减，着生藻类密度、生物量和LCBD随海拔梯度单调递增，而着生藻类均匀度并无明显的海拔分布格局。海拔对年均温、年降水量、日均辐射量、电导率、溶解氧、浊度和流速有显著影响。进一步解析海拔对着生藻类密度、生物量和多样性指数的影响机制，发现海拔主要通过影响年均温、年降水量和日均辐射量等区域气候因子进而影响局地环境因子间接影响着生藻类分布格局。电导率、溶解氧和浊度是着生藻类海拔分布格局的关键驱动因子。该研究结果为了解河流生物多样性对气候变化的响应规律提供了重要信息，为河流生物多样性保护提供了科学依据。

关键词: 着生硅藻, 密度, 生物量, 物种丰富度, 均匀度, 样点对β多样性的贡献（LCBD）, 海拔分布格局