Fast-decaying tree litter reduces the temperature sensitivity of soil carbon decomposition by increasing microbial necromass carbon

Abstract

Improvements in stocks and stability of forest soil organic carbon can be achieved through the management of tree species. Given the long lifespan of trees and their role as the keystone species in forested ecosystems, decisions regarding tree species management can have a significant impact on soil carbon balance, with effects that may persist for decades. Here, a common garden experiment involving five temperate tree species in northeast China was conducted to quantify the influence of tree species on soil carbon dynamics, including its fractions (mineral-associated organic carbon, particulate organic carbon, and microbial necromass carbon), microbial properties (biomass and activities), and the temperature sensitivity of soil carbon decomposition (Q₁₀). We observed that the decomposition of high-quality litter by soil microbes resulted in increased microbial biomass but decreased microbial biomass-specific enzyme activities and respiration. Although there was no significant difference in soil carbon among tree species, the sources of soil carbon varied among species. Specifically, tree species producing high-quality litter contributed to elevated microbial and fungal necromass carbon. Microbial necromass carbon was positively correlated with soil mineral-associated organic carbon, although tree species had no significant effect on mineral-associated organic carbon. The Q₁₀ increased with longer litter turnover time, as well as with higher microbial biomass-specific oxidase activity and respiration, but decreased with greater litterfall production, microbial biomass, and microbial necromass carbon. Overall, our findings indicate that fast-decaying tree litter increases soil microbial necromass carbon and decreases Q₁₀. This is the first study to establish a connection between Q₁₀ with microbial necromass carbon using experimental data. Moreover, the tree species-specific origins of soil carbon and their influence on Q₁₀ should be considered when managing forests as carbon sinks in the context of future global warming.