Stabilization Mechanisms of Isotope Labeled Carbon in Soil Under Moisture Pulses and Conservation Agricultural Management

Authors: Li, Lidong; SCHAEFFER, SEAN - University Of Tennessee

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2020
Publication Date: N/A
Citation: N/A

Interpretive Summary: Stabilization of carbon in soil will be beneficial for soil quality and agriculture. It also can mitigate climate change. Adding carbon substrate to soil can increase soil carbon content. Soil drying-rewetting cycles can affect the stabilization of carbon substrate in soil. Our results indicate that soil drying-rewetting cycles can cause losses of the carbon substrates in soil, and conservation agricultural management, such as nitrogen-fixing cover cropping, can mitigate some of the negative effects.

Technical Abstract: Understanding the mechanisms of carbon (C) stabilization in soil under the influence of moisture pulses is essential for predicting the stability of terrestrial C in the face of climate change. Conservation agricultural management is widely recognized to mitigate climate change through soil C stabilization or retention. We conducted a 24-day mesocosm incubation using an agricultural soil under 36 years of conservation agricultural management including winter cover cropping and no-tillage farming. We added 13C-labeled simple (glucose) or complex (corn litter) C substrates to mesocosms, applied different frequencies of moisture pulses, and traced the fate of the added glucose-C and corn-C in labile and recalcitrant soil C pools. Structural equation modeling was used to quantify the effect sizes of the short-term moisture pulses and the long-term conservation management on the stabilization of the added glucose-C and corn-C in soil. Our results show that the added corn-C, which is more biochemically complex, had a lower recovery in microbial biomass than glucose-C after 24 days. Compared to rewetting the soil, extended drought increased accumulation of the added C in microbial biomass, extractable organic C, and H2O2-resistant C, with the exception of corn-C which decreased in microbial biomass. Vetch, a nitrogen-fixing cover crop, appeared to stabilize the added glucose-C and corn-C via facilitating incorporation into the H2O2-resistant fraction of soil C. Moisture pulses disrupted macroaggregates and induced release of microaggregates, which may lead to destabilization of the added C. Structural equation models show that the multiple moisture pulses destabilized the added glucose-C and corn-C in soil, while the conservation management could mitigate some of these effects. Our study shows that conservation agriculture can help to improve resilience of agroecosystem function in relation to soil C storage and stability in the face of climate change.