Species diversity and chemical properties of litter influence non-additive effects of litter mixtures on soil carbon and nitrogen cycling

Abstract

Decomposition of litter mixtures generally cannot be predicted from the component species incubated in isolation. Therefore, such non-additive effects of litter mixing on soil C and N dynamics remain poorly understood in terrestrial ecosystems. In this study, litters of Mongolian pine and three dominant understory species and soil were collected from a Mongolian pine plantation in Northeast China. In order to examine the effects of mixed-species litter on soil microbial biomass N, soil net N mineralization and soil respiration, four single litter species and their mixtures consisting of all possible 2-, 3- and 4-species combinations were added to soils, respectively. In most instances, species mixing produced synergistic non-additive effects on soil microbial biomass N and soil respiration, but antagonistic non-additive effects on net N mineralization. Species composition rather than species richness explained the non-additive effects of species mixing on soil microbial biomass N and net N mineralization, due to the interspecific differences in litter chemical composition. Both litter species composition and richness explained non-additive soil respiration responses to mixed-species litter, while litter chemical diversity and chemical composition did not. Our study indicated that litter mixtures promoted soil microbial biomass N and soil respiration, and inhibited net N mineralization. Soil N related processes rather than soil respiration were partly explained by litter chemical composition and chemical diversity, highlighting the importance of functional diversity of litter on soil N cycling.

Mixing crop residues induces a synergistic effect on microbial biomass and an additive effect on soil organic matter priming

“…Applying crop residues as a mixture resulted in a significantly ( P < 0.05) greater microbial biomass compared to the average effect of applying each of the residues individually, indicating a synergistic effect of crop residue diversity on soil microbial biomass (Figure 1). This result was consistent with a microcosm experiment which found 38.2% higher soil microbial biomass N in soils receiving a mixture of residues than would be expected from residues of individual species (Mao et al, 2017). The mixture also exhibited greater total microbial biomass than any of the non-mixture treatments (Figure S4), suggesting its synergistic effect is more likely to be caused by facilitation between residues rather than by the disproportionate effect of individual species.…”

“…The mixture also exhibited greater total microbial biomass than any of the non-mixture treatments (Figure S4), suggesting its synergistic effect is more likely to be caused by facilitation between residues rather than by the disproportionate effect of individual species. The common explanation in the literature for why a mixture induces synergistic effect on decomposition rate is that N is transferred from low C/N residues to high C/N residues to satisfy microbial stochiometric requirement (Gartner and Cardon, 2004; Mao et al, 2017). If the availability of N is the limiting factor in our experiment, we would see the treatment receiving clover residues (which had the highest C/N ratio) exhibiting the smallest microbial biomass.…”

“…A majority of the previous studies have explored the effects of mixtures on litter decomposition and associated C cycling and nutrient release (e.g. nitrogen mineralization and immobilization) by focusing on leaf litter decomposition in forest ecosystems (Castro-Díez et al, 2019; Gartner and Cardon, 2004; Mao et al, 2017). Even the most recent meta-analysis on litter mixtures only focused on litter mass loss due to decomposition (Porre et al, 2020).…”

Applying cover crop residues as diverse mixtures increases initial microbial assimilation of crop residue‐derived carbon

“…The mixture also exhibited greater total microbial biomass than any of the non-mixture treatments (although not significantly greater in the case of radish; Figure S4), suggesting that a mixture of cover crop residues has the capability to increase soil microbial biomass more than the "best performing" monoculture. The most common explanation for synergistic interactions during the decomposition of litter in a mixture is that N is transferred from low C:N residues to high C:N residues to satisfy microbial stoichiometric requirements (Gartner & Cardon, 2004;Mao et al, 2017). If the availability of N is the limiting factor in our experiment, we would expect to see the treatment receiving clover residues (which had the highest C:N ratio) exhibiting the smallest microbial biomass.…”

“…The most common explanation for synergistic interactions during the decomposition of litter in a mixture is that N is transferred from low C:N residues to high C:N residues to satisfy microbial stoichiometric requirements (Gartner & Cardon, 2004; Mao et al, 2017). If the availability of N is the limiting factor in our experiment, we would expect to see the treatment receiving clover residues (which had the highest C:N ratio) exhibiting the smallest microbial biomass.…”