Abstract
Warming can increase the efflux of carbon dioxide (CO2) from soils and can potentially feedback to climate change. In addition to warming, the input of labile carbon can enhance the microbial activity by stimulating the co-metabolism of recalcitrant soil organic matter (SOM). This is particularly true with SOM under invaded ecosystems where elevated CO2and warming may increase the biomass of invasive species resulting in higher addition of labile substrates. We hypothesized that the input of labile carbon would instigate a greater soil organic carbon (SOC) loss with warming compared to the ambient temperature. We investigated this by incubating soils collected from a native pine (Pinus taeda) forest to which labile carbon from the invasive species kudzu (Pueraria lobata) was added. We evaluated the microbial extracellular enzyme activity, molecular composition of SOC and the temperature sensitivity of soil CO2efflux under warming and labile carbon addition. After 14 months of soil incubation, the addition of labile C through kudzu extract increased the activity of β-1,4-glucosidase compared with the control. However, the activity of N-acetyl-β-D-glucosaminidase and fungal biomass (ergosterol) decreased with labile carbon addition. The activity of peroxidase increased with warming after 14 months of soil incubation. Although the carbon content of incubated soils did not vary with substrate and temperature treatments, the molecular composition of SOC indicated a general decrease in biopolymers such as cutin, suberin, long-chain fatty acids, and phytosterol with warming and an increasing trend of microbial-derived compounds with labile substrate addition. In soils that received an addition of labile C, the macro-aggregate stability was higher while the temperature sensitivity of soil C efflux was lower compared with the control. The increase in aggregate stability could enhance the physical protection of SOC from microbial decomposition potentially contributing to the observed pattern of temperature sensitivity. Our results suggest that warming could preferentially accelerate the decomposition of recalcitrant compounds while the addition of labile substrates could enhance microbial-derived compounds that are relatively resistant to further decomposition. Our study further emphasizes that global change factors such as plant invasion and climate change can differentially alter soil microbial activity and the composition of SOC.
Highlights
Warming can accelerate the efflux of carbon dioxide (CO2) from the soil carbon pool to the atmospheric pool, potentially creating a positive feedback to climate change (Field et al, 2007; Wu et al, 2011)
The influence of warming and labile substrate addition on the quantity of soil carbon has been studied independently, less is known about the interactive effects of these two factors (Zhang et al, 2013) on soil carbon stocks and the molecular composition of resulting soil organic carbon (SOC), which could have implications on the stability of soil carbon
We evaluated the combined effect of warming and addition of labile C substrates on microbial biomass and microbial extracellular enzyme activity
Summary
Warming can accelerate the efflux of carbon dioxide (CO2) from the soil carbon pool to the atmospheric pool, potentially creating a positive feedback to climate change (Field et al, 2007; Wu et al, 2011). The input of labile carbon could subsidize the energy requirement of microbes for the production of oxidative enzymes This in turn could stimulate the co-metabolism of relatively recalcitrant SOM (Kuzyakov et al, 2000) leading to the loss of soil C. Both warming and the input of labile substrates could accelerate soil CO2 efflux, which could potentially feedback to climate change. The influence of warming and labile substrate addition on the quantity of soil carbon has been studied independently, less is known about the interactive effects of these two factors (Zhang et al, 2013) on soil carbon stocks and the molecular composition of resulting SOC, which could have implications on the stability of soil carbon
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