全球气候变暖对凋落物分解的影响

Impacts of global warming on litter decomposition

凋落物分解作为生态系统核心过程,参与生态系统碳的周转与循环,影响生态系统碳的收支平衡,调控生态系统对全球气候变暖的反馈结果。全球气候变暖通过环境因素、凋落物数量和质量以及分解者3个方面,直接或间接地作用于凋落物分解过程,并进一步影响土壤养分周转和碳库动态。气候变暖可通过升高温度和改变实际蒸散量等环境因素直接作用于凋落物分解。气候变暖可引起植物物种短期内碳、氮和木质素等化学性质的改变以及群落中物种组成的长期变化从而改变凋落物质量。在凋落物分解过程中,土壤分解者亚系统作为主要生命组分(土壤动物和微生物)彼此相互作用、相互协调共同参与调节凋落物的分解过程。凋落物分解可以通过改变土壤微生物量、微生物活动和群落结构来加快微生物养分的固定或矿化,以形成新的养分利用模式来改变土壤有机质从而对气候变化做出响应。未来凋落物分解的研究方向应基于大尺度跨区域分解实验和长期实验,关注多个因子交互影响下,分解过程中碳、氮养分释放、地上/地下凋落物分解生物学过程与联系、分解者亚系统营养级联效应等方面。

Litter decomposition is an important ecosystem process that plays a key role in global carbon dynamics and balance. Decomposition can influence soil carbon cycling and carbon sequestration, and consequently feedback into ecosystem climate change responses. Global warming can have negative, neutral, or positive effects on litter decomposition rates by affecting environmental factors, litter quality, and decomposers. Changes in evapotranspiration and other environmental factors like soil moisture induced by global warming can exert a direct effect on litter decomposition. However, the effects of climate change on leaf litter decomposition vary across ecosystems. Generally, leaf litter decomposes faster under warmer conditions in both grassland ecosystem and wetland ecosystem. However, leaf litter decomposition rate does not show a consistent response to warming in forest ecosystems due to the interaction of a number of environmental factors involved in the forest ecosystem. In addition, climate change associated changes in environmental factors such as soil moisture in cold-temperate regions has a stronger effect on leaf litter decomposition. Changes in plant communities driven by global warming can indirectly affect litter decomposition by altering litter quality and their inputs. Warming can induce change in the litter quality and quantity of a plant community, with or without changing the composition of that community. In term of litter inputs, global warming may enhance leaf litter production and net photosynthetic productivity of plants more in temperate and boreal forest than in tropical and subtropical forests, which leads to a decomposition rate increase in the former areas. Decomposition is one of the most important biological processes impacting soil carbon storage. Leaf litter transfers carbon from the living plant. Carbon is released into the soil through the process of decomposition. So the impact of global warming on the forest carbon cycle depends on the balance between accumulation and decomposition of litter. Positive feedback comes from the direct effects of warming on litter decomposition, which means warming will increase litter decomposition and release more CO2 into the atmosphere. However, negative feedback from warming may manifest as changes in leaf quality, quantity, or time retained, all of which can indirectly influence litter decomposition. Decomposer communities （i.e., soil fauna and microorganisms） may also affect litter decomposition rates in response to global warming. Warming can shift biomass, metabolic rate, and community composition of decomposers, and consequently influence litter decomposition rates and nutrient input into soils. In addition, the coexistence of soil fauna and microorganisms from different trophic has greater impacts on litter decomposition than those decomposers appear alone, whereas little is known about the effects of interactions with these biotic organisms in litter decomposition. We reviewed previous studies to elucidate how warming affects litter decomposition from the perspective of three variables： environmental factors, litter quality, and decomposers. We argue that long-term and large-scale experiments are essential to study responses and feedback of litter decomposition to climate change. Key scientific questions such as the mechanisms underlying nutrient release from decomposing litters, correlation between aboveground and belowground litter decomposition, and interactions of decomposers from different trophic levels on litter decomposition, should be settled urgently.