Soil Microbial Biomass Size and Nitrogen Availability Influence N2o Production

Abstract

Microbial biomass (MB) plays a critical role in the soil nitrogen (N) cycle. However, the effect of MB size on nitrous oxide (N2O) production from soils, and how this is influenced by N availability and exogenous carbon (C) input, remains unknown. For this study, two soils originating from the same parent materials but differing in SOC contents due to 23 years of different land management were selected. The size of the soil MB was changed by pre-incubating soils with glucose. The soils with altered MB size were then treated with different quality of ryegrass residues (varied in C: N ratio) with or without N to investigate how the production of N2O responds to changes in soil MB size and how this response is affected by soil N availability and exogenous C input.      Higher N2O productions were observed in a grassland soil (GS) compared to a conventionally cropped soil (CS). In CS and GS, the increased size of the soil MB promoted N2O production by 76% and 40%, respectively. However, the effect only stimulated N2O emission in CS after the amendment of ryegrass residue. The treatment of ryegrass residue with low C: N ratio combined with N addition produced the greatest N2O in GS treatments, while high C: N ratio of residue with N produced the most N2O in CS treatments. The interaction between increased soil MB size and N addition played a key role in controlling N2O production from GS. The results highlight the importance of soil MB size and its impact on N2O emissions in response to C or N addition and different soil properties, which are influenced by land management and climate change. To effectively mitigate greenhouse gas emissions, it is essential to consider the interactive effects between soil properties, residue quality, and MB size.

Keywords: microbial biomass, ryegrass, C:N, N2O emission, soil organic carbon