Seasonality amplifies nitrogen availability’s influence on rhizosphere priming effect from a permafrost peatland soil

Northern permafrost peatlands represent a substantial carbon reservoir; however, the rhizosphere priming effect (RPE) and its response to increased nitrogen (N) availability due to warming or thawing permafrost soils remain poorly characterized. This study investigated how varying N additions (0, 12, and 24 g N m−2 yr−1; N0, N1, and N2) influenced the RPE of Eriophorum vaginatum L. using 13CO2 tracing and phospholipid fatty acid technology-stable isotope probing techniques in a northern permafrost peatland. We observed a negative RPE, attributed to reduced microbial biomass and enzyme activity in rhizosphere soil compared to bulk soil. Nitrogen additions lessened this negative RPE by 44.0%–94.8% compared to N0 treatment. In planted systems, N addition stimulated SOM-derived CO2 respiration by 31.0%-122.8%. Nitrogen addition enhanced plant biomass (31.7%-75.6%), and elevated plant C:P and N:P ratios, whereas the plant C:N ratio decreased. The impact on carbon use efficiency (CUE) in the rhizosphere soil was season-dependent, showing a significant enhancement in late spring but a marked decline in summer. Increased Gram-negative bacteria were responsible for 64.9%-75.8% of the total PLFA increase, and their 13C incorporation constituted 54.8%-60.7% of the total microbial 13C uptake. Conversely, in unplanted systems, N addition reduced SOM-derived CO2 respiration by 8.0%–23.4%. This was linked to decreased microbial biomass (primarily Gram-negative bacteria) and enzyme activity, alongside improved microbial CUE. Gram-negative bacteria appear to be the primary microbial group influencing RPE. Our findings demonstrate a complex regulation of RPE in permafrost peatlands, driven by plant stoichiometry, microbial community structure, and seasonal variation. This study offers crucial insights into the mechanisms governing RPE in these sensitive ecosystems.