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

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.