Soil fauna accelerate litter mixture decomposition globally, especially in dry environments

Abstract

1. More than half of the net primary production in terrestrial ecosystems returns to the soil through leaf litter fall and decomposition. In terrestrial ecosystems, litter constitutes a mixture of mainly senescent foliage from multiple species.Yet, the effect of litter mixing on litter decomposition rate remains ambiguous. Quantification of the soil fauna contribution and inclusion of their interaction with litter could remove the prevailing ambiguity, as soil fauna might influence the direction and magnitude of litter mixture effects on decomposition.2. We carried out a global meta-analysis to elucidate how soil fauna influenced litter mixture decomposition rate based on 55 published studies with 873 fauna inclusion/exclusion observations in field litterbag experiments. We hypothesized that soil fauna inclusion in litter mixture experiments would cause a positive change in the magnitude of mixed litter decomposition. That is, the presence of soil fauna would lead to synergistic litter mixture effects while the absence of soil fauna would lead to antagonistic litter mixture effects. Furthermore, we hypothesized that soil fauna would have a greater positive impact on the litter mixture effect in environments with low precipitation.3. While litter mixture had a neutral effect on decomposition on average across studies, non-additive mixture effects were common, with a key role for soil fauna, which generally enhanced decomposition rate compared to the component single-species litters. In contrast, fauna exclusion resulted in diminished decomposition rate overall. The overall synergistic soil fauna effect on litter mixture decomposition increased under low precipitation. Under high precipitation, the litter mixture effect was positive in the absence of soil fauna but non-significant in the presence of fauna. Climate imposes a great effect on litter mixture, with synergistic effects increasing towards the equator. 4. Synthesis. These results highlight the importance of soil fauna in mixed litter decomposition, most strongly in dry environments. In this era of global climate change, where some regions are projected to become drier, soil fauna might compensate the expected slower decomposition of litter by increasingly enhancing litter mixture decomposition.

Litter decomposition and nutrient release from monospecific and mixed litters: Comparisons of litter quality, fauna and decomposition site effects

“…Reports have indicated that a mesh size of 50 μm permits the entry of micro‐organisms and microfauna, 1 mm permits the entry of micro‐ and mesofauna, and 5 mm permits the entry of the complete decomposer community, including macrofauna (Makkonen et al, 2012). Soil fauna effects on decomposition rates are modulated by climate and litter quality, which vary based on the biome (Njoroge et al, 2022). For instance, García‐Palacios et al (2013) found that the effect of soil fauna on decomposition rates in tropical wet forests is stronger than that in tropical dry forests.…”

Litter accumulation and fire risks show direct and indirect climate-dependence at continental scale

“…Similarly, observed rates of decomposition of single species are seldom the same as rates of decomposition when foliage of two or more species are decomposing together 7 , 22 , 23 . While activities of decomposing soil fauna and microbial decomposers (fungi, bacteria etc) are often tightly interrelated 20 , 21 , physical proximity helps determine the biologically facilitated transfers of energy and nutrients, especially from more decomposable tissues to less decomposable tissues.…”

“…LIDET 17 , CIDET 18 ). Important findings are that (a) longer-term rates of decomposition are over-estimated by shortterm studies [17][18][19] , (b) litter decomposition is seldom complete and (c) including or excluding important decomposer fauna via the size of litterbag mesh significantly affects measured rates of decomposition 20,21 .…”

Functional identity drives tree species richness‐induced increases in litterfall production and forest floor mass in young tree communities

“…Litterbags have significant limitations, including exclusion of larger soil animals from litterbags by using mesh that is smaller than their body width. Previous evidence showed that soil fauna access to the litterbag determines the degree and direction of the influence of litter diversity on litter decomposition (Hättenschwiler & Gasser, 2005; Njoroge et al ., 2022). Confounding factors associated with litterbags include microclimate, handling and leaching losses, and the proportion of fragmented, undecomposed litter that falls or moves out of litterbags in the field.…”