Contrasting effects of multifactorial carbon, nitrogen, and phosphorus amendments on soil microbial carbon-use efficiency and biomass turnover in a subtropical grassland and forest soil

Abstract

Soil microbial carbon-use efficiency (CUE) and biomass turnover have been identified as important drivers of biogeochemical processes; however, we lack a comprehensive understanding of the factors driving them. Here, we tested how multifactorial carbon (C), nitrogen (N), and phosphorus (P) amendments affect microbial CUE and biomass turnover in a subtropical grassland and forest soil. In the grassland soil, we observed significant (50%) decreases in microbial CUE with C, CP, and CNP addition and increased microbial CUE with N addition (+20%). On the other hand, microbial biomass turnover sharply increased in all treatments receiving C and decreased with P and NP addition. In the forest soil, resource amendment had no effect on microbial CUE, whereas microbial biomass turnover was lower under P and NP additions than under C-amended soils. Combined nutrient additions frequently produced responses that could not be predicted from single-resource amendments, revealing strong interactions among nutrient effects. Our findings highlight the importance of considering nutrient interactions when predicting microbial controls on soil C and nutrient cycling under changing resource regimes and land-use.