Nitrogen enrichment enhances thermal acclimation of soil microbial respiration

As the climate warms, the feedback between soil carbon (C) and climate can decrease in magnitude over time due to the thermal acclimation of microbial respiration. However, the strength of microbial thermal acclimation is highly uncertain, partly because the response of microbial respiration is regulated by multiple environmental factors acting simultaneously rather than by temperature alone. Here we use a theoretical representation method to visually quantify the magnitude of thermal acclimation of microbial respiration based on a 9-year two-way factorial experiment involving warming and multilevel nitrogen (N) enrichment treatments in alpine permafrost. The results showed that mass-specific respiration rates were significantly lower in warmed soils when N enrichment was higher. Post-acclimation Q(10) was as much as 1.6 times higher for soils sampled from no N enrichment treatment than from the highest N enrichment concentration treatment. These results suggested that respiration rate reductions under warming likely occurred through N-induced changes in the soil and microbial community and that the thermal strength acclimation gradually increases as N enrichment increases. We identified two contrasting pathways by which N enrichment appears to affect the strength of thermal acclimation using the structural equation model-1) via an enhancement of acclimation caused by soil acidification and 2) a weakening of acclimation caused by the inhibition of soil C availability and stimulation of soil C-degrading enzymes. Our findings emphasize the importance of considering multiple environmental change factors in shaping the strength of thermal acclimation when predicting future soil C-climate feedbacks.

Automated summary

As climate warms, the strength of microbial thermal acclimation and its effects on soil carbon feedback may be influenced by multiple environmental factors, including nitrogen concentration and soil acidity. This study found that under warming conditions, higher nitrogen enrichment reduced the mass-specific respiration rates in alpine permafrost soils. The strength of thermal acclimation was found to increase as nitrogen enrichment increased, but the pathways by which nitrogen affects acclimation can vary.