Precipitation variability drives the reduction of total soil respiration and heterotrophic respiration in response to nitrogen addition in a temperate forest plantation

Abstract

How precipitation mediates the responses of soil respiration (Rs) and its components, i.e., heterotrophic respiration (Rh) and autotrophic respiration (Ra), to N addition remains uncertain. In an 11-year-old temperate larch plantation in northern China, we investigated the responses of Rs, Rh, and Ra to three N-addition rates (i.e., control: no N addition; low N addition: 20 kg N ha−1 year−1; and high N addition: 50 kg N ha−1 year−1) over a 6-year period that experienced high variability in precipitation. In the control plot, Rs and Rh during wet years were significantly higher than values in both normal (by 37% and 62%, respectively) and dry years (by 19% and 39%, respectively). These results indicated that increased precipitation may stimulate soil microbial biomass and activity which in turn increase Rh and thus Rs. Interestingly, Rs was not affected by N addition in normal or dry years, whereas it was negatively affected by N addition in wet years, primarily due to the decrease in Rh during the summer following N addition. Furthermore, N addition significantly increased Ra in the spring of wet years, because the N limitation was largely alleviated after N addition, and thus, roots might be more active due to higher soil water and N availability. Overall, our findings emphasize the importance of incorporating the mediating role of increased precipitation on soil C loss via respiratory processes and corresponding responses to N addition into models, with the goal of reducing uncertainty in the predictions of carbon–climate feedbacks.