Department of Forest Ecology and Management, Swedish University of Agricultural Sciences (SLU), Umeå, Sweden.
Asian School of the Environment, Nanyang Technological University, Singapore, Singapore.
Ecology. 2020 Dec;101(12):e03170. doi: 10.1002/ecy.3170. Epub 2020 Oct 6.
Changes in plant communities can have large effects on ecosystem carbon (C) dynamics and long-term C stocks. However, how these effects are mediated by environmental context or vary among ecosystems is not well understood. To study this, we used a long-term plant removal experiment set up across 30 forested lake islands in northern Sweden that collectively represent a strong gradient of soil fertility and ecosystem productivity. We measured forest floor CO exchange and aboveground and belowground C stocks for a 22-yr experiment involving factorial removal of the two dominant functional groups of the boreal forest understory, namely ericaceous dwarf shrubs and feather mosses, on each of the 30 islands. We found that long-term shrub and moss removal increased forest floor net CO loss and decreased belowground C stocks consistently across the islands irrespective of their productivity or soil fertility. However, we did see context-dependent responses of respiration to shrub removals because removals only increased respiration on islands of intermediate productivity. Both CO exchange and C stocks responded more strongly to shrub removal than to moss removal. Shrub removal reduced gross primary productivity of the forest floor consistently across the island gradient, but it had no effect on respiration, which suggests that loss of belowground C caused by the removals was driven by reduced litter inputs. Across the island gradient, shrub removal consistently depleted C stocks in the soil organic horizon by 0.8 kg C/m . Our results show that the effect of plant functional group diversity on C dynamics can be relatively consistent across contrasting ecosystems that vary greatly in productivity and soil fertility. These findings underline the key role of understory vegetation in forest C cycling, and suggest that global change leading to changes in the relative abundance of both shrubs and mosses could impact on the capacity of boreal forests to store C.
植物群落的变化会对生态系统碳（C）动态和长期 C 储量产生重大影响。然而，这些影响是如何被环境背景所介导的，或者在不同的生态系统中是如何变化的，目前还不是很清楚。为了研究这个问题，我们利用在瑞典北部的 30 个森林湖泊岛屿上建立的一个长期植物去除实验，这些岛屿共同代表了土壤肥力和生态系统生产力的强烈梯度。我们对森林地表 CO 交换以及地上和地下 C 储量进行了 22 年的实验测量，该实验涉及对北方森林林下两种主要功能群（即石南矮小灌木和羽毛藓）在 30 个岛屿中的每个岛屿上进行双因子去除。我们发现，长期的灌木和苔藓去除会增加森林地表的净 CO 损失，并降低地下 C 储量，这在整个岛屿上是一致的，而与它们的生产力或土壤肥力无关。然而，我们确实看到了呼吸对灌木去除的依赖于背景的响应，因为只有在生产力处于中等水平的岛屿上，去除灌木才会增加呼吸。CO 交换和 C 储量对灌木去除的响应都比对苔藓去除的响应更强烈。灌木去除一致地降低了整个岛屿梯度上的森林地表总初级生产力，但对呼吸没有影响，这表明去除引起的地下 C 损失是由减少的凋落物输入驱动的。在整个岛屿梯度上，灌木去除一致地使土壤有机层中的 C 储量减少了 0.8kg C/m²。我们的研究结果表明，植物功能群多样性对 C 动态的影响在生产力和土壤肥力差异很大的不同生态系统中可以相对一致。这些发现强调了林下植被在森林 C 循环中的关键作用，并表明导致灌木和苔藓相对丰度变化的全球变化可能会影响北方森林储存 C 的能力。
