The effect of nitrogen addition on soil respiration from a nitrogen-limited forest soil

We investigated how soil respiration (Rs), heterotrophic respiration (Rh) and rhizosphere respiration (Rr) respond to nitrogen addition in a 21-yr-old larch (Larix principis-rupprechtii) plantation in North China. Three levels of nitrogen treatments (control, no nitrogen addition; low-N, 20 kg N ha(-1) yr(-1); high-N, 50 kg N ha(-1) yr(-1)) were established in May 2010. Rs, Rh and Rr were then measured during the growing seasons from 2011 to 2013. Nitrogen addition significantly reduced Rs by 10.0% under low-N treatment and by 12.5% under high-N treatment. Rh and Rr showed different responses to nitrogen addition. Nitrogen addition had no significant effects on growing season fluxes of Rh during the observation periods, but Rr was decreased by similar to 37% and similar to 31% under the low-N and high-N treatments, respectively. Averaged across the three growing seasons, the mean rate of Rs decreased from 2.47 +/- 0.39 mu mol m(-2) s(-1) in the control plots to 2.22 +/- 0.34 mu mol m(-2) s(-1) in low-N plot and 2.16 +/- 0.30 mu mol m(-2) s(-1) in the high-N plot. Rr contributed about 111% and 76% of the observed reduction of Rs in low and high-N plots, respectively. In addition, elevated nitrogen input also reduced the temperature coefficients (Q(10)) of Rh and Rr. Compared to the control, nitrogen additions significantly decreased Q(10) of Rh and Rr in high-N plots by 7% and 13%, respectively. Overall, our results suggest that the reduction in Rs can mainly be attributed to the decrease in rhizosphere respiration in our nitrogen-limited plantation. With global temperature rising, nitrogen deposition may increase carbon sequestration in forest ecosystems, not only by reducing carbon loss by Rs, but also by reducing the temperature coefficients of Rh and Rr. (C) 2014 Elsevier B.V. All rights reserved.