Priming effect is inhibited by 12-year field nitrogen addition in a boreal forest with the extent depending on substrate carbon type

Abstract

Plant carbon inputs can influence soil organic carbon (SOC) decomposition rate, i.e., the priming effect, which can be regulated by nitrogen (N) addition. How long-term N addition affects the priming effect remains unclear yet, especially in boreal forests with severer N limitation. Here, soils were collected from a 12-year in-situ N addition field experiment in a boreal forest, and were incubated with ¹³C-labeled cellulose and glucose. Further, a global data synthesis was conducted to compare the effect of N addition on priming between simple and complex C types. The results showed that cellulose-induced priming effect was inhibited by on average 150 % by 12-yr N addition. Hydrolytic enzymes were decreased, while oxidases were increased, suggesting a shift in microbial C use strategy in response to C limitation. Subsequently, microbial C use efficiency (CUE) was increased by 12-yr N addition. 68.3 % of the variation in the priming effect among all the treatments was explained by microbial CUE, hydrolytic enzymes and oxidases, reflecting the important role in regulating the priming effect. Compared to glucose, the N inhibited effect on cellulose-induced priming was greater, while the N inhibited effect on substrate-derived CO₂-C was lower, broadly supporting the microbial N mining and C utilization hypotheses. Further, the N-inhibited effect on priming caused by complex C was greater than that by simple C across the globe. We highlight that substrate C type should be considered for accurately assessing SOC decomposition via the priming effect in the context of N deposition in boreal forests.