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碳通量与森林动态:热带雨林林冠空隙中枯立木分解的增加。

Carbon flux and forest dynamics: Increased deadwood decomposition in tropical rainforest tree-fall canopy gaps.

机构信息

School of Environmental Sciences, University of Liverpool, Liverpool, UK.

School of Biological Sciences, Faculty of Science, University of Bristol, Bristol, UK.

出版信息

Glob Chang Biol. 2021 Apr;27(8):1601-1613. doi: 10.1111/gcb.15488. Epub 2021 Jan 27.

Abstract

Tree mortality rates are increasing within tropical rainforests as a result of global environmental change. When trees die, gaps are created in forest canopies and carbon is transferred from the living to deadwood pools. However, little is known about the effect of tree-fall canopy gaps on the activity of decomposer communities and the rate of deadwood decay in forests. This means that the accuracy of regional and global carbon budgets is uncertain, especially given ongoing changes to the structure of rainforest ecosystems. Therefore, to determine the effect of canopy openings on wood decay rates and regional carbon flux, we carried out the first assessment of deadwood mass loss within canopy gaps in old-growth rainforest. We used replicated canopy gaps paired with closed canopy sites in combination with macroinvertebrate accessible and inaccessible woodblocks to experimentally partition the relative contribution of microbes vs. termites to decomposition within contrasting understorey conditions. We show that over a 12 month period, wood mass loss increased by 63% in canopy gaps compared with closed canopy sites and that this increase was driven by termites. Using LiDAR data to quantify the proportion of canopy openings in the study region, we modelled the effect of observed changes in decomposition within gaps on regional carbon flux. Overall, we estimate that this accelerated decomposition increases regional wood decay rate by up to 18.2%, corresponding to a flux increase of 0.27 Mg C ha year that is not currently accounted for in regional carbon budgets. These results provide the first insights into how small-scale disturbances in rainforests can generate hotspots for decomposer activity and carbon fluxes. In doing so, we show that including canopy gap dynamics and their impacts on wood decomposition in forest ecosystems can help improve the predictive accuracy of the carbon cycle in land surface models.

摘要

由于全球环境变化,热带雨林中的树木死亡率正在上升。当树木死亡时,森林树冠层会出现空隙,碳会从活体转移到枯木池中。然而,人们对树冠空隙对分解者群落活动和枯木腐烂速度的影响知之甚少。这意味着区域和全球碳预算的准确性不确定,尤其是考虑到雨林生态系统结构的持续变化。因此,为了确定树冠开口对木材腐烂速度和区域碳通量的影响,我们首次评估了原始雨林中树冠空隙内枯木质量损失。我们使用复制的树冠空隙与封闭的树冠站点相结合,结合宏观无脊椎动物可及和不可及的木块,实验性地划分了微生物与白蚁对分解作用的相对贡献,在不同的林下条件下。我们表明,在 12 个月的时间里,与封闭的树冠站点相比,树冠空隙中的木材质量损失增加了 63%,而这种增加是由白蚁驱动的。我们使用 LiDAR 数据来量化研究区域树冠开口的比例,并用模型来模拟观测到的分解作用变化对区域碳通量的影响。总的来说,我们估计这种加速分解使区域木材腐烂率增加了高达 18.2%,相当于区域碳预算中尚未考虑的 0.27 Mg C ha 年通量增加。这些结果首次深入了解热带雨林中小规模干扰如何产生分解者活动和碳通量的热点。通过这样做,我们表明,包括树冠空隙动态及其对森林生态系统中木材分解的影响,可以帮助提高陆地表面模型中碳循环的预测精度。

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