PS 46-20
Decrease in rhizosphere respiration caused the reduction of soil respiration under nitrogen addition in a Larix principis rupprechtii plantation in North China
It has widely been documented that anthropogenic nitrogen (N) input often reduces soil respiration (Rs) in forest ecosystem. However, there is still dispute on which component of Rs, heterotrophic respiration (Rh) or rhizosphere respiration (Rr), contributes more to the decrease in Rs under N enrichment. In this study, we investigated how Rs, Rh and Rr responded to N addition in a 21-yr-old Larix principis-rupprechtii plantation in North China.Three levels of N treatments (control, no N addition; low-N, 20 kg N/ha/yr; high-N, 50 kg N/ha/yr) were established since May 2010. Rs, Rh and Rr were measured during snow-free seasons from 2011 to 2013.
Results/Conclusions
N 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 N addition. N addition had no significant effects on annual fluxes of Rh during the observed periods, but Rr was decreased by ~37% and ~31% under low and high N treatment, respectively. Average across the three year, the annual mean rate of Rs was decreased from 2.47 ± 0.39 µmol m-2 s-1 in the control plots to 2.22 ± 0.34 µmol m-2 s-1 in low N plot and 2.16 ± 0.30 µmol m-2 s-1 in high N plot. Rr contributed about 111% and 76%, respectively, of the observed reduction of Rs in low and high N plots. In addition, elevated N input also reduced the temperature coefficients (Q10) of Rh and Rr. Compared to control, N additions significantly decreased Q10 of Rh and Rr in high-N plots by 7% and 13%, respectively. Overall, our results suggest that the reduction in Rs was mainly attributed by the decrease in rhizosphere respiration in our N limited plantation. With global temperature rising, N deposition may increase carbon sequestration in forest ecosystems, not only by reducing carbon loss by Rs, also by reducing the temperature coefficients of Rh and Rr.