西藏高寒草原湿润度梯度下植物群落特征空间格局及其驱动因子

西藏高原是中国高寒生态系统类型和生物多样性均聚集的区域之一,其中以高寒典型草原和高寒草甸草原为主生态系统类型,但其系统活力、组织力和恢复力均较弱,容易受到全球气候变化的影响,表现出极强的脆弱性。目前青藏高原草地生态系统植物群落分布状况与其变化规律以及对各种环境因子的反应研究多集中于站点尺度或样带尺度,但研究结果尚有较大的不确定性。研究于西藏地区沿着不同的湿润度梯度选择14处高寒草原区样地,通过植物群落调查、土壤理化性质分析,探索草本植被群落空间格局对气候因子响应特征及其主要驱动因子,其结果为青藏高原天然草地保护和可持续利用提供基础科学数据支撑。结果表明: (1)研究区内依据湿润度分区可分为干旱区、微干区、微润区和湿润区4类;研究区1971-2021年的气候数据分析发现,北部的干旱程度在逐渐减轻,而南部在1991-2010阶段干旱化趋势逐渐加强,整个研究区的湿润度指数均在下降;(2)植物群落调查发现不同植物功能群的变化各有差异,莎草科地上生物量随湿润度增加而增加,杂类草地上生物量呈现单峰趋势,而其他植物功能群无明显规律;湿润度较高的微润区间植物群落的Shannon-Wiener指数、Simpson指数、丰富度指数、均匀度指数均高于其他湿润度区间;(3)土壤理化性质分析发现高湿润度区域的土壤含水量、全氮、硝态氮、铵态氮、速效磷含量均为最高;对各环境因子与植物群落特征指标进行相关性、主成分分析后构建结构方程模型,发现直接影响西藏高寒草原植物群落特征变化因子为湿润度,土壤含水量和土壤pH,且都表现为显著的负效应(P<0.05),同时湿润度对土壤含水量和土壤全量养分产生了显著的正向影响(P<0.05),进而影响着西藏高原高寒草原不同植物功能群的分布、多样性、地上生物量。

Spatial pattern of plant communities along wetness gradient in Alpine grassland of Xizang and their driving factors

Xizang Plateau is one of the regions with extremely concentrated ecological system types and biodiversity in China''s alpine ecosystem. The high-altitude typical grasslands and alpine meadows are the main grassland ecosystem types. Due to its weak system vitality, organization and resilience, it is strongly vulnerable to the impact of global climate change. For many years, the studies on the distribution of plant communities and their changes and responses to various environmental factors in the grassland ecosystem of Xizang Plateau have been focused on site scale or transect scale, but the results are still uncertain. We selected 14 sample plots of alpine grassland areas along different wettability gradients in Xizang region. Through investigation of vegetation community and analysis of soil physical and chemical properties, we explored the response characteristics of spatial pattern of herbaceous vegetation community to climate factors and its main driving factors. The results provided basic scientific data support for the protection and sustainable utilization of natural grassland on Xizang Plateau. The results show that: (1) the research region can be divided into arid zone, semi-arid zone, semi-humid zone, and humid zone. The aridity degree in the northern part was gradually decreasing from 1971 to 2021, while that in the southern part was gradually increasing during 1991-2010. The humidity index of the whole study area was decreasing. (2) The investigation of plant community found that the changes of different plant functional groups were different. The aboveground biomass of Cyperaceae increased with the increasing humidity, while that of Miscellaneous grass showed a unimodal trend, the other community had no obvious regularity. The Shannon-Wiener diversity index, Simpson index, richness index, and evenness index of plant community in semi-humid zones with higher humidity were higher than those in other humidity zones. (3) The analysis of soil physical and chemical properties found that the soil moisture content, total nitrogen, nitrate nitrogen, ammonium nitrogen, and available phosphorus content in high-humidity areas were the highest. Based on the correlation and principal component analysis of various environmental factors and plant community characteristics, the structural equation model was established. The factors that directly affected the changes of plant community characteristics in alpine grasslands on Xizang Plateau were wettability, soil moisture content, and soil pH, showing the significantly negative effects (P<0.05). However, wettability had significantly positive effect on soil water content and soil total nutrient (P<0.05), which further affected the distribution, diversity and aboveground biomass of different plant functional groups in alpine grasslands on Xizang Plateau.