From microbial physiology to soil carbon stabilization: Controls across land use, management, and soil types

Microbial growth and carbon use efficiency (CUE) play a central role in soil organic carbon (SOC) cycling by regulating microbial biomass production and subsequent necromass contributions to persistent SOC pools. Due to dynamic responses of CUE to environmental changes, it remains unclear how microbial physiological trade-offs translate into SOC stabilization via necromass retention. In this study, we investigated how microbial respiration, growth, and CUE are regulated by land-use type, management intensity, and soil properties across 300 grassland and forest plots in three regions of Germany. We aim to disentangle the abiotic and biotic drivers of microbial contribution to SOC accumulation along gradients of land-use intensity and biodiversity.
Grasslands exhibited higher microbial growth and respiration than forests (growth ≈ 0.35 vs 0.12 mg C kg⁻¹ h⁻¹, respiration ≈ 2.3 vs 1.0 mg C kg⁻¹ h⁻¹), while CUE did not differ between land-use types. In forests, tree species strongly influenced microbial physiology with higher growth and CUE in deciduous stands than in coniferous stands. Management intensity in grasslands, particularly nitrogen inputs, exerted positive indirect effects on microbial growth and CUE, whereas forest management had predominantly negative effects on CUE through direct and indirect changes in abiotic soil properties. Microbial biomass carbon and soil pH emerged as key drivers in forests, while grasslands showed more dynamic responses, likely driven by resource availability in soil.
To examine how microbial growth and carbon use efficiency (CUE) translate into necromass accumulation, we compared organic soils derived from degraded peat with mineral soils at different depths that differ fundamentally in substrate availability and soil properties. Mineral soils contained a higher proportion of microbial-derived carbon per unit SOC than organic soils, despite greater substrate availability and higher microbial activity in organic soils, consistent with stronger microbial necromass retention in mineral soils.
Together, these results show that microbial carbon dynamics and contributions to SOC are regulated by land use, management, and soil type through distinct controls on microbial growth, carbon use efficiency, and necromass retention, thereby influencing SOC persistence across managed ecosystems.