Global effects of plant litter alterations on soil CO₂ to the atmosphere

Abstract

Soil respiration (Rs) is the largest terrestrial carbon (C) efflux to the atmosphere and is predicted to increase drastically through global warming. However, the responses of Rs to global warming are complicated by the fact that terrestrial plant growth and the subsequent input of plant litter to soil are also altered by ongoing climate change and human activities. Despite a number of experiments established in various ecosystems around the world, it remains a challenge to predict the magnitude and direction of changes in Rs and its temperature sensitivity (Q ) due to litter alteration. We present a meta-analysis of 100 published studies to examine the responses of Rs and Q to manipulated aboveground and belowground litter alterations. We found that 100% aboveground litter addition (double litter) increased Rs by 26.1% (95% confident intervals, 18.4%-33.7%), whereas 100% aboveground litter removal, root removal and litter + root removal reduced Rs by 22.8% (18.5%-27.1%), 34.1% (27.2%-40.9%) and 43.4% (36.6%-50.2%) respectively. Moreover, the effects of aboveground double litter and litter removal on Rs increased with experimental duration, but not those of root removal. Aboveground litter removal marginally increased Q by 6.2% (0.2%-12.3%) because of the higher temperature sensitivity of stable C substrate than fresh litter. Estimated from the studies that simultaneously tested the responses of Rs to aboveground litter addition and removal and assuming negligible changes in root-derived Rs, "priming effect" on average accounted for 7.3% (0.6%-14.0%) of Rs and increased over time. Across the global variation in terrestrial ecosystems, the effects of aboveground litter removal, root removal, litter + root removal on Rs as well as the positive effect of litter removal on Q increased with water availability. Our meta-analysis indicates that priming effects should be considered in predicting Rs to climate change-induced increases in litterfall. Our analysis also highlights the need to incorporate spatial climate gradient in projecting long-term Rs responses to litter alterations.

Plant diversity loss reduces soil respiration across terrestrial ecosystems

“…Plants play a decisive role in regulating Rs since they are the principal pathways through which carbon enters the soil (Chen & Chen, ). Biomass production increases with plant species diversity and trait heterogeneity due to complementary resource utilization among constituent species in species‐rich ecosystems (Hooper et al, ; Zhang, Chen, & Reich, ).…”

“…Biomass production increases with plant species diversity and trait heterogeneity due to complementary resource utilization among constituent species in species‐rich ecosystems (Hooper et al, ; Zhang, Chen, & Reich, ). The higher biomass production in species‐rich ecosystems is expected to increase Rs primarily by increasing respiration in living roots and their associated rhizomicrobial and microbial communities (Chen & Chen, ; Kuzyakov & Gavrichkova, ). Higher plant diversity can also increase soil microbial respiration because of a higher quantity and multiplicity of plant‐derived food resources that enter the soil as well as expanded niches for microbes associated with a higher microenvironment variability and habitat complexity (Chapman & Newman, ; Eisenhauer et al, ; Hector, Beale, Minns, Otway, & Lawton, ; Hooper et al, ).…”

“…Although the positive tree species mixture effects on productivity are suggested to be stronger in boreal than temperate forests (Paquette & Messier, ), a global meta‐analysis shows that positive mixture effects on productivity are consistent across forest biomes and between planted and natural forests (Zhang et al, ). In the meantime, the responses of Rs to plant inputs tend to decrease with reduced water availability induced by high temperatures, due to reduced litter decomposition (Chen & Chen, ; Vogel et al, ; Zhu & Cheng, ). We, therefore, expected that the effects of plant mixtures on Rs would differ among ecosystem types and change with temperature and water availability.…”

Benchmark estimates for aboveground litterfall data derived from ecosystem models

“…A meta-analysis of 100 published experimental studies found that a 100% aboveground litter addition (i.e. double litter) increased heterotrophic respiration by 26.1% (Chen and Chen 2018). Additionally, increased inputs of fresh organic matter resulting from litterfall could result in 'priming effects'.…”

“…Litterfall is a particularly key process for determining the carbon and nutrient cycling of terrestrial ecosystems, and it controls the main respiration substrates on the forest floor (Roig et al 2005, Chen andChen 2018). The magnitude of litterfall regulates the rate of soil respiration and soil organic carbon content indirectly (Sayer 2006, Hansen et al 2009, Neumann et al 2018.…”