Abstract
Input of labile carbon may accelerate the decomposition of existing soil organic matter (priming effect), with the priming intensity depending on changes in soil nitrogen availability after permafrost thaw. However, experimental evidence for the linkage between the priming effect and post-thaw nitrogen availability is unavailable. Here we test the hypothesis that elevated nitrogen availability after permafrost collapse inhibits the priming effect by increasing microbial metabolic efficiency based on a combination of thermokarst-induced natural nitrogen gradient and nitrogen addition experiment. We find a negative correlation between the priming intensity and soil total dissolved nitrogen concentration along the thaw sequence. The negative effect is confirmed by the reduced priming effect after nitrogen addition. In contrast to the prevailing view, this nitrogen-regulated priming intensity is independent of extracellular enzyme activities but associated with microbial metabolic efficiency. These findings demonstrate that post-thaw nitrogen availability regulates topsoil carbon dynamics through its modification of microbial metabolic efficiency.
Highlights
Input of labile carbon may accelerate the decomposition of existing soil organic matter, with the priming intensity depending on changes in soil nitrogen availability after permafrost thaw
The partitioning of C substrate between microbial biomass and carbon dioxide (CO2) production, is a key microbial physiological property that determines the fate of soil organic C (SOC)[30,31]
The addition of 13C-labelled glucose significantly promoted the release of unlabelled CO2 from soils at all stages of permafrost collapse (P < 0.05; Fig. 1a–d), resulting in positive priming along the thaw sequence
Summary
Input of labile carbon may accelerate the decomposition of existing soil organic matter (priming effect), with the priming intensity depending on changes in soil nitrogen availability after permafrost thaw. Postthaw changes in soil nutrients, moisture, texture and pH15,16 may influence SOM turnover by altering the priming intensity[8,17,18] Among these changes, the widespread increase in nitrogen (N) availability after permafrost collapse[16,19], driven by enhanced N mineralization[16] and the additional N released from thawing permafrost[20], may play an important role in regulating the priming intensity, since both vegetation growth and topsoil microbial activity in arctic[21,22] and alpine ecosystems[23,24,25] are N limited. This N-induced deceleration of soil C release is attributed to the increased microbial metabolic efficiency that occurs under high-N conditions
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