Microbial turnover mediates nonlinear response of soil N₂O and CH₄ fluxes to diversity loss

Abstract

Loss of soil microbial diversity is accelerating worldwide, yet how this loss alters soil greenhouse gas fluxes remains poorly understood. Here, we provide experimental evidence that diversity loss affects nitrous oxide (N₂O) and methane (CH₄) fluxes through nonlinear, trait-mediated pathways. Using soil microcosm dilution gradients established across three land-use types (forest, grassland, and cropland), we linked shifts in community diversity with key physiological traits: carbon use efficiency (CUE), nitrogen use efficiency (NUE), and turnover rate. Over a 118-day incubation, soil N₂O flux exhibited a pronounced hump-shaped response: moderate diversity loss stimulated emissions, whereas severe loss suppressed them through the breakdown of functional redundancy. Strikingly, even moderate diversity loss reversed soils from CH₄ sinks to net sources. Microbial turnover consistently emerged as the core driver of both N₂O and CH₄ fluxes, with additional contributions from the turnover interactions with CUE and NUE. Variance partitioning further showed that microbial physiological traits explained 62% of CH₄ flux variation and 59% of N₂O flux variation. Together, these findings highlight the pivotal role of microbial traits in mediating soil biodiversity-function relationships. They also emphasize the importance of incorporating trait-based processes into Earth system models to improve predictions of soil climate feedbacks.

Graphical abstract

Keywords

microbial diversity / microbial carbon use efficiency / nitrogen use efficiency / global change / greenhouse gases

Highlight

	● Moderate diversity loss reverses soils from a net CH4 sink to a source.
	● Moderate microbial diversity loss increases soil N2O emissions.
	● Microbial turnover rate is the key physiological trait governing N2O and CH4 fluxes.
	● Microbial traits are stronger predictors of GHG fluxes than microbial diversity.

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