Soil health management enhances microbial nitrogen cycling capacity and activity

Authors: HU, JIALIN - University Of Tennessee; KONKEL, JULIE - University Of Tennessee; Jin, Virginia; SCHEIDER, LIESEL - University Of Tennessee; SCHAEFFER, SEAN - University Of Tennessee; DEBRUYN, JENNIFER - University Of Tennessee

Submitted to: mSphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2020
Publication Date: 1/13/2021
Citation: Hu, J., Konkel, J., Jin, V.L., Scheider, L., Schaeffer, S., Debruyn, J. 2021. Soil health management enhances microbial nitrogen cycling capacity and activity. mSphere. 6(1). Article e01237-20. https://doi.org/10.1128/mSphere.01237-20.
DOI: https://doi.org/10.1128/mSphere.01237-20

Interpretive Summary: ervation agriculture practices that promote soil health have distinct and lasting effects on nitrogen cycling microbial populations. In particular, using a leguminous winter cover crop (hairy vetch) promoted expression of key nitrogen (N) cycle functional genes, equaling or exceeding the effects of inorganic N fertilizer. Hairy vetch also left a legacy on soil: nitrogen cycling microbes continued to be active after cover crop termination in the spring through the main growing season. By examining both genes and transcripts of genes involved in soil N cycling, we revealed relationships between microbial functional capacity and activity and associated nitrogen pools and processes in the field. Importantly, we showed that functional capacity (i.e. gene abundances) was a better predictor of some parts of the N cycle such as N2O emissions, while activity (i.e. transcript abundances) was more highly correlated with other processes such as nitrification.

Technical Abstract: Soil microbial transformations of nitrogen (N) can be affected by soil health management practices. Here, we report in situ seasonal dynamics of the population size (gene copy abundances) and functional activity (transcript copy abundances) of five bacterial genes involved in soil N cycling (AOB amoA, nifH, nirK, nirS, and nosZ) in a long-term continuous cotton production system under different management practices (cover crops, tillage, and inorganic N fertilization). Hairy vetch (Vicia villosa Roth), a leguminous cover crop, most effectively promoted the expression of N-cycle genes, which persisted after cover crop termination throughout the growing season. Moreover, we observed similarly high or even higher N-cycle gene transcript abundances under vetch with no fertilizer as no cover crop with N fertilization throughout the cover crop peak and cotton growing seasons (April, May, and October). Further, both the gene and transcript abundances of amoA and nosZ were positively correlated to soil nitrous oxide (N2O) emissions. We also found that the abundances of amoA genes and transcripts both positively correlated to field and incubated net nitrification rates. Together, our results revealed relationships between microbial functional capacity and activity and in situ soil N transformations under different agricultural seasons and soil management practices.