Soil quality, leaf litter quality, and microbial biomass interactively drive soil respiration in a microcosm experiment

Abstract

Soil respiration plays a central role in global carbon dynamics, and small changes in the magnitude of soil respiration could have large impacts on atmospheric CO2 concentrations. Heterotrophic soil respiration mainly comes from microbial mineralization of soil organic matter and decomposition of plant litter, yet only a few studies have addressed the combined effects of interactions among leaf litter quality, soil quality, and microbial biomass on soil respiration. We conducted a microcosm experiment using three soils from three forest sites representing a gradient in soil quality, comprised of soil pH and C:N ratio, and six tree litter types (from the same forests), encompassing a gradient in leaf nutrient and lignin concentrations. We followed soil CO2 emissions, soil basal respiration (measured as O2-consumption), and microbial biomass over twelve weeks to examine variation in response to leaf litter and soil quality and their interactions. Our results show that soil CO2 emissions increased significantly with soil quality and leaf litter quality respectively, and these effects were mediated by interactions with soil microbial biomass. Moreover, we found idiosyncratic interactive effects of leaf litter quality and microbial biomass on soil CO2 emissions across the gradient in soil quality. The sensitivity of soil respiration to soil quality and the interactions between leaf litter quality and soil microbial biomass suggests that global change drivers altering forest composition and soil community composition may have significant cascading effects on the soil carbon cycle.

Keywords

• Aboveground-belowground interactions
• carbon cycle
• decomposition
• leaf litter C dynamics
• leaf litter traits
• context-dependency