Institute of Ecology, College of Urban and Environmental Sciences and Key Laboratory for Earth Surface Processes, Peking University, Beijing, China.
Department of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland.
Ecology. 2019 Mar;100(3):e02624. doi: 10.1002/ecy.2624. Epub 2019 Feb 25.
Positive biodiversity-ecosystem-functioning (BEF) relationships are commonly found in experimental and observational studies, but how they vary in different environmental contexts and under the influence of coexisting life forms is still controversial. Investigating these variations is important for making predictions regarding the dynamics of plant communities and carbon pools under global change. We conducted this study across 433 shrubland sites in northern China. We fitted structural equation models (SEMs) to analyze the variation in the species-richness-biomass relationships of shrubs and herbs along a wetness gradient and general liner models (GLMs) to analyze how shrub or herb biomass affected the species-richness-biomass relationship of the other life form. We found that the positive species-richness-biomass relationships for both shrubs and herbs became weaker or even negative with higher water availability, likely indicating stronger interspecific competition within life forms under more benign conditions. After accounting for variation in environmental contexts using residual regression, we found that the benign effect of greater facilitation by a larger shrub biomass reduced the positive species-richness-biomass relationships of herbs, causing them to become nonsignificant. Different levels of herb biomass, however, did not change the species-richness-biomass relationship of shrubs, possibly because greater herb biomass did not alter the stress level for shrubs. We conclude that biodiversity in the studied plant communities is particularly important for plant biomass production under arid conditions and that it might be possible to use shrubs as nurse plants to facilitate understory herb establishment in ecological restoration.
正向生物多样性-生态系统功能（BEF）关系在实验和观察研究中很常见，但它们在不同的环境背景下以及在共存生命形式的影响下如何变化仍然存在争议。研究这些变化对于预测全球变化下植物群落和碳库的动态非常重要。我们在中国北方的 433 个灌木地进行了这项研究。我们通过结构方程模型（SEMs）来分析灌木和草本植物在湿润梯度上的物种丰富度-生物量关系的变化，并通过广义线性模型（GLMs）来分析灌木或草本植物生物量如何影响另一种生命形式的物种丰富度-生物量关系。我们发现，灌木和草本植物的正向物种丰富度-生物量关系随着水分供应的增加而减弱甚至变为负相关，这可能表明在更有利的条件下，种间竞争更强。在使用残差回归考虑环境背景变化后，我们发现较大的灌木生物量所带来的良性促进作用降低了草本植物的正向物种丰富度-生物量关系，使其变得不显著。然而，不同水平的草本植物生物量并没有改变灌木的物种丰富度-生物量关系，这可能是因为较大的草本植物生物量没有改变灌木的压力水平。我们得出结论，在干旱条件下，研究中植物群落的生物多样性对于植物生物量的产生尤为重要，并且可能可以利用灌木作为护理植物来促进生态恢复中林下草本植物的建立。
