Influence of soil N availability on priming effects depending on temperature

The priming effect (PE) is a globally important regulator of soil organic matter (SOM) turnover that closely correlates with N availability. PE intensity is usually higher under N-limited conditions and lower under N inputs, but this relationship may depend on temperature. To investigate whether temperature influences the role of N availability in the PE, we conducted a 200-d incubation of soil samples amended with 13C-labeled rice litter at 15 °C, 25 °C, and 35 °C, adding NH4+ and NO3− to examine impacts of increased N availability on PE. Litter amendment caused net N immobilization and exacerbated soil N limitation, thereby reducing SOM mineralization (which was negative PE) at 25 °C and 35 °C. N addition mitigated the negative PE intensity, with a marked decrease at 25 °C (from −21 % to −5 %) and a marginal impact at 35 °C. Microbial biomass C and N contents peaked at 25 °C but declined by ∼20 % at 35 °C. The ratio of C- to N-acquiring enzyme activities, as well as that for gene copies, was lower at 25 °C than at 35 °C, suggesting N limitation at 25 °C. In contrast, rapid labile C depletion and high microbial metabolic quotient caused severe microbial C limitation at 35 °C, which forced microorganisms to increase abundance of genes involved in recalcitrant compound decomposition. Warming to 35 °C also shifted microbial communities from the dominance of r-strategists (25 °C) to that of K-strategists (35 °C), as indicated by increases in the ratio of K- to r-related functional genes. The dominance of K-strategists, which generally have low N demands, rendered PE less sensitive to N inputs at 35 °C. Our findings underscore the temperature-dependent nature of soil N versus C limitations, which may lead to lower microbial N limitation and decreased impact of N availability on PE under a warming climate.