Simulated nitrogen deposition significantly reduces soil respiration in an evergreen broadleaf forest in western China

Abstract

Soil respiration is the second largest terrestrial carbon (C) flux; the responses of soil respiration to nitrogen (N) deposition have far-reaching influences on the global C cycle. N deposition has been documented to significantly affect soil respiration, but the results are conflicting. The response of soil respiration to N deposition gradients remains unclear, especially in ecosystems receiving increasing ambient N depositions. A field experiment was conducted in a natural evergreen broadleaf forest in western China from November 2013 to November 2015 to understand the effects of increasing N deposition on soil respiration. Four levels of N deposition were investigated: control (Ctr, without N added), low N (L, 50 kg N ha−1·a−1), medium N (M, 150 kg N ha−1·a−1), and high N (H, 300 kg N ha−1·a−1). The results show that (1) the mean soil respiration rates in the L, M, and H treatments were 9.13%, 15.8% (P < 0.05) and 22.57% (P < 0.05) lower than that in the Ctr treatment (1.56 ± 0.13 μmol·m−2·s−1), respectively; (2) soil respiration rates showed significant positive exponential and linear relationships with soil temperature and moisture (P < 0.01), respectively. Soil temperature is more important than soil moisture in controlling the soil respiration rate; (3) the Ctr, L, M, and H treatments yielded Q10 values of 2.98, 2.78, 2.65, and 2.63, respectively. N deposition decreased the temperature sensitivity of soil respiration; (4) simulated N deposition also significantly decreased the microbial biomass C and N, fine root biomass, pH and extractable dissolved organic C (P < 0.05). Overall, the results suggest that soil respiration declines in response to N deposition. The decrease in soil respiration caused by simulated N deposition may occur through decreasing the microbial biomass C and N, fine root biomass, pH and extractable dissolved organic C. Ongoing N deposition may have significant impacts on C cycles and increase C sequestration with the increase in global temperature in evergreen broadleaf forests.

The Additions of Nitrogen and Sulfur Synergistically Decrease the Release of Carbon and Nitrogen from Litter in a Subtropical Forest

“…The +N treatment decreased the rate of litter decomposition in our study, supporting our first hypothesis that N addition would decrease litter decomposition in the study forest. This result was in agreement with most of the previous studies in subtropical forests [21,28]. This phenomenon can be explained by two mechanisms.…”

“…In this study, we carried out a two-year field experiment in a subtropical evergreen broadleaved forest in this rainy area to examine the responses of the litter decomposition and the release of C, N, and P to the addition of N and S. The aims of this study are to improve the understanding of the effects of N and S deposition on litter nutrient release in subtropical evergreen broadleaved forests in the studied area and to provide a reference for the management of these forests under the scenario of a sustained rise in N and S depositions. Previous studies in broadleaved forests in this rainy area have shown that the addition of N decreased soil microbial biomass [27][28][29] and the activities of soil C-cycle enzymes [30], suggesting that N input may negatively affect litter decomposition and nutrient release [21,31,32]. We thus hypothesized that (1) N addition would inhibit litter decomposition and decrease the release of C, N, and P in the study forest.…”

“…The rainy zone of Western China is an ecotone between the Sichuan Plateau and the Sichuan Basin (Figure 1) [28,34]. The mean annual wet N and S depositions from 2008 to 2010 in this rainy area were 95 kg N ha −1 y −1 and 193 kg S ha −1 y −1 , respectively [25,26].…”

“…Considering the high levels of atmospheric deposition and the observations of previous N and S addition studies in the study area [25,[27][28][29][30], 150 kg N ha −1 y −1 and 300 kg S ha −1 y −1 were added in the present experiment, consisting of the control (CK, no added N or S), added N (+N, added 150 kg N ha −1 y −1 ), added S (+S, added 300 kg S ha −1 y −1 ), and added N and S (+NS, added 150 kg N ha −1 y −1 and 300 kg S ha −1 y −1 ) treatments. The N and S were from urea and sodium sulfate, respectively.…”

Responses of Soil C-, N-, and P-Hydrolyzing Enzyme Activities to N and P Addition in an Evergreen Broad-Leaved Forest in Southwest China

“…(Chen et al 2018a;, soil respiration) and decomposition of litter(Whittinghill et al 2012;Cenini et al 2016). In our previous studies in the same region, we reported that N addition signi cantly suppressed soil heterotrophic respiration(Wei et al 2020), and decomposition of litter and the degradation of lignin and cellulose(Zhou et al 2018;Tie et al 2020a). …”