论文部分内容阅读
生物多样性与生态系统功能的正相关关系已被广泛报道,其主要来源于对草原生态系统的研究.然而,该结论并不一定适用于更复杂的环境,例如具有不同垂直层次的森林.举例而言,已有研究表明上层乔木树种丰富度与林下生产力降低有关.树种丰富度是否会通过增加(由于生境异质性)或降低(通过增强竞争)资源的可利用性进而影响林下生产力,以及林下生产力是否受树种特性的影响更大,这些影响机制都可能会随着时间的推移而改变.此外,研究还表明,丰富度-生产力关系随着环境背景的变化而改变.本研究利用可以操控树种丰富度的实验林场研究了这些不同垂直层位里的时间和环境动态.在中国亚热带森林生物多样性与生态系统功能(BEF-China)研究计划的框架下,我们在3年时间里沿树种丰富度梯度反复采集林下生物量样本,研究了不同环境处理中树种丰富度、树种特性和时间对林下生物量的影响.尽管我们发现乔木层特性对林下生物量有显著和一致的影响,但是树种丰富度对后者却不具有这种影响.另外,在森林结构层之间,可能并不存在单一的、具有普遍性的上层乔木树种丰富度与林下生产力的相关关系,并且与上层乔木相关的环境因素(如透光率)对林下生产力的贡献程度会随着时间而变化.总体而言,我们的结果表明,在研究森林结构层之间的关系时应将时间动态变化考虑在内.“,”Aims Positive biodiversity-ecosystem functioning relationships have been widely reported,predominately from grassland ecosystems.However,this does not necessarily have to apply accordingly in more complex situations such as in forests across different vertical strata.For instance,overstorey tree species richness has been shown to be associated with a lower understorey productivity.Whether or not tree species richness effects add to understorey productivity by increasing (i.e.due to habitat heterogeneity) or reducing resource availability (i.e.through increasing competition) and whether understorey productivity is indeed being governed more strongly by tree species identity are likely to change over time.Moreover,studies also suggested that richness-productivity relationships change with the environmental context.Using an experimental forest plantation with manipulated tree species richness,this study examined these temporal and environmental dynamics across strata.Methods In the context of the Biodiversity-Ecosystem Functioning project in subtropical China (BEF-China),we made use of understorey biomass samples repeatedly collected over a time period of 3 years along a tree species richness gradient.The effects of tree species richness,tree species identities and time were studied across different environmental treatments for their impact on understorey biomass.Important Findings While we found significant and consistent tree layer identity effects on understorey biomass,no such effect was encountered for tree species richness.Our results also indicate that among structural layers in forests,there might not be a single,generalizable overstorey species richness-understorey productivity relationship,and that the extent as to which overstorey-related environmental factors such as light transmittance contribute to understorey productivity change with time.Overall,we demonstrate that temporal dynamics should be considered when studying relationship among structural layers in forests.