Abstract：
Plant communities are being exposed to changing environmental conditions all around the globe, leading to alterations in plant diversity, community composition, and ecosystem functioning. For herbaceous understorey communities in temperate forests, responses to global change are postulated to be complex, due to the presence of a tree layer that modulates understorey responses to external pressures such as climate change and changes in atmospheric nitrogen deposition rates. Multiple investigative approaches have been put forward as tools to detect, quantify and predict understorey responses to these global-change drivers, including, among others, distributed resurvey studies and manipulative experiments. These investigative approaches are generally designed and reported upon in isolation, while integration across investigative approaches is rarely considered. In this study, we integrate three investigative approaches (two complementary resurvey approaches and one experimental approach) to investigate how climate warming and changes in nitrogen deposition affect the functional composition of the understorey and how functional responses in the understorey are modulated by canopy disturbance, that is, changes in overstorey canopy openness over time. Our resurvey data reveal that most changes in understorey functional characteristics represent responses to changes in canopy openness with shifts in macroclimate temperature and aerial nitrogen deposition playing secondary roles. Contrary to expectations, we found little evidence that these drivers interact. In addition, experimental findings deviated from the observational findings, suggesting that the forces driving understorey change at the regional scale differ from those driving change at the forest floor (i.e., the experimental treatments). Our study demonstrates that different approaches need to be integrated to acquire a full picture of how understorey communities respond to global change.
摘要：
植物群落暴露在全球不断变化的环境条件下，导致植物多样性的改变，社区组成,和生态系统功能。对于温带森林中的草本植物下层群落，对全球变化的反应被认为是复杂的，由于树层的存在，可以调节底层对气候变化和大气氮沉积速率变化等外部压力的响应。已经提出了多种调查方法作为检测的工具，量化和预测底层对这些全球变化驱动力的反应，包括,其中,分布式复测研究和操纵实验。这些调查方法通常是孤立地设计和报告的，虽然很少考虑跨调查方法的整合。在这项研究中,我们整合了三种研究方法（两种互补的重新调查方法和一种实验方法），以研究气候变暖和氮沉积的变化如何影响底层的功能组成，以及如何通过冠层扰动调节底层的功能响应。也就是说,随着时间的推移，高层冠层开放的变化。我们的重新调查数据显示，底层功能特征的大多数变化代表了对冠层开放性变化的响应，而宏观气候温度和空中氮沉降的变化则起次要作用。与预期相反,我们几乎没有发现这些司机互动的证据。此外,实验结果偏离了观察结果，这表明在区域尺度上驱动底层变化的力量不同于在森林底层驱动变化的力量(即，实验处理)。我们的研究表明，需要整合不同的方法，以全面了解底层社区如何应对全球变化。
