Increased simulated precipitation frequency promotes greenhouse gas fluxes from the soils of seasonal fallow croplands

Introduction

Farmlands are key sources of greenhouse gas (GHG) emissions, which are susceptible to changes in precipitation regimes. The soils of seasonal fallow contribute approximately half of annual GHG emissions from farmlands, but the effect of precipitation frequency on soil GHG emissions from seasonal fallow croplands remains virtually unknown.

Materials and Methods

We conducted a microcosm study to evaluate the response of nitrous oxide (N₂O), methane (CH₄) and carbon dioxide (CO₂) fluxes from typical paddy and upland soils to the changes in watering frequency simulating precipitation scenarios of subtropical regions during seasonal fallow. We also analyzed changes of soil properties and biotic characteristics associated with GHG emissions, including abundances of soil denitrifiers (nirK, nirS, nosZI and nosZII genes), methanotrophs (pmoA gene) and methanogens (mcrA gene) to altered watering frequency.

Results

Increased watering frequency led to overall increases in soil N₂O and CO₂ fluxes compared with low frequency. Compared with low frequency, high watering frequency decreased CH₄ flux from the paddy soil by 3.5 times, while enhanced CH₄ flux from the upland soil by 60%. Furthermore, the increased watering frequency had positive effects on cumulative N₂O and CO₂ fluxes from the upland soil, whereas no similar trend was observed for the paddy soil. Hierarchical partitioning analyses showed that N₂O fluxes from the paddy soil were mostly related to nitrogen availability, and mcrA gene abundance had more than 90% of relative independent effects on CH₄ and CO₂ fluxes from the paddy soil. For the upland soil, nosZ (60.34%), pmoA (53.18%) and nir (47.07%) gene abundances were important predictors of N₂O, CH₄ and CO₂ fluxes, respectively.

Conclusion

Our results demonstrate that increased watering frequency facilitates GHG emissions by changing soil properties and functional gene abundances. These findings provide new insights into GHG fluxes from seasonal fallow croplands in response to altered precipitation patterns.