Yao Zhenyu, Xin Yue, Yang Liu, Zhao Liqing, Ali Arshad
Inner Mongolia Key Laboratory of Grassland Ecology and School of Ecology and Environment, Inner Mongolia University, Hohhot, China.
Yinshanbeilu Grassland Eco-hydrological National Observation and Research Station, China Institute of Water Resources and Hydropower Research, Beijing, China.
Front Plant Sci. 2022 Dec 1;13:999636. doi: 10.3389/fpls.2022.999636. eCollection 2022.
Although the relationships between species diversity and aboveground biomass (AGB) are highly debated in grassland ecosystems, it is not well understood how climatic factors influence AGB directly and indirectly plant coverage and species diversity in large-scale grasslands along a topographic gradient. In doing so, we hypothesized that climatic factors would regulate plant coverage, species diversity and AGB due to maintaining plant metabolic and ecological processes, but the relationship of plant coverage with AGB would be stronger than species diversity due to covering physical niche space.
To test the proposed hypothesis, we collected data for calculations of species richness, evenness, plant coverage and AGB across 123 grassland sites (i.e., the mean of 3 plots in each site) dominated by in northern China. We used a structural equation model for linking the direct and indirect effects of topographic slope, mean annual precipitation and temperature on AGB plant coverage, species richness, and evenness through multiple complex pathways.
We found that plant coverage increased AGB, but species evenness declined AGB better than species richness. Topographic slope influenced AGB directly but not indirectly plant coverage and species diversity, whereas temperature and precipitation increased with increasing topographic slope. Regarding opposing mechanisms, on the one hand, precipitation increased AGB directly and indirectly plant coverage as compared to species richness and evenness. On the other hand, temperature declined AGB indirectly plant coverage but increased species evenness as compared to species richness, whereas the direct effect was negligible.
Our results show that niche complementarity and selection effects are jointly regulating AGB, but these processes are dependent on climatic factors. Plant coverage promoted the coexistence of species but depended greatly on precipitation and temperature. Our results highlight that precipitation and temperature are two key climatic drivers of species richness, evenness, plant coverage and AGB through complex direct and indirect pathways. Our study suggests that grasslands are sensitive to climate change, i.e., a decline in water availability and an increase in atmospheric heat. We argue that temperature and precipitation should be considered in grassland management for higher productivity in the context of both plant coverage and species diversity which underpin animals and human well-being.
尽管在草原生态系统中，物种多样性与地上生物量（AGB）之间的关系备受争议，但在沿地形梯度的大规模草原中，气候因素如何直接和间接影响AGB、植物覆盖度和物种多样性，目前尚不清楚。在此过程中，我们假设气候因素会通过维持植物的代谢和生态过程来调节植物覆盖度、物种多样性和AGB，但由于植物覆盖度占据了物理生态位空间，其与AGB的关系将比物种多样性更强。
为了验证上述假设，我们收集了中国北方123个以[具体植物]为主的草原样地（即每个样地3个小区的平均值）的数据，用于计算物种丰富度、均匀度、植物覆盖度和AGB。我们使用结构方程模型，通过多个复杂途径来连接地形坡度、年平均降水量和温度对AGB、植物覆盖度、物种丰富度和均匀度的直接和间接影响。
我们发现植物覆盖度增加了AGB，但物种均匀度比物种丰富度更能降低AGB。地形坡度直接影响AGB，但对植物覆盖度和物种多样性没有间接影响，而温度和降水量随地形坡度的增加而增加。在相反的机制方面，一方面，与物种丰富度和均匀度相比，降水量通过植物覆盖度直接和间接增加了AGB。另一方面，温度通过植物覆盖度间接降低了AGB，但与物种丰富度相比，通过物种均匀度增加了AGB，而直接影响可以忽略不计。
我们的结果表明，生态位互补和选择效应共同调节着AGB，但这些过程依赖于气候因素。植物覆盖度促进了物种的共存，但很大程度上依赖于降水量和温度。我们的结果强调，降水量和温度是通过复杂的直接和间接途径影响物种丰富度、均匀度、植物覆盖度和AGB的两个关键气候驱动因素。我们的研究表明，草原对气候变化很敏感，即水资源可用性下降和大气热量增加。我们认为，在草原管理中应考虑温度和降水量，以在支撑动物和人类福祉的植物覆盖度和物种多样性的背景下提高生产力。
