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.