Nitrogen deposition may enhance soil carbon storage via change of soil respiration dynamic during a spring freeze-thaw cycle period

www.nature.com/scientificreports OPEN received: 19 February 2016 accepted: 15 June 2016 Published: 30 June 2016 Nitrogen deposition may enhance soil carbon storage via change of soil respiration dynamic during a spring freeze-thaw cycle period Guoyong Yan1,2,*, Yajuan Xing1,3,*, Lijian Xu1,*, Jianyu Wang2, Wei Meng2, Qinggui Wang1,2, Jinghua Yu4, Zhi Zhang1, Zhidong Wang1, Siling Jiang1, Boqi Liu2 & Shijie Han4 As crucial terrestrial ecosystems, temperate forests play an important role in global soil carbon dioxide flux, and this process can be sensitive to atmospheric nitrogen deposition. It is often reported that the nitrogen addition induces a change in soil carbon dioxide emission in growing season. However, the important effects of interactions between nitrogen deposition and the freeze-thaw-cycle have never been investigated. Here we show nitrogen deposition delays spikes of soil respiration and weaken soil respiration. We found the nitrogen addition, time and nitrogen addition×time exerted the negative impact on the soil respiration of spring freeze-thaw periods due to delay of spikes and inhibition of soil respiration (p < 0.001). The values of soil respiration were decreased by 6% (low-nitrogen), 39% (medium-nitrogen) and 36% (high-nitrogen) compared with the control. And the decrease values of soil respiration under medium- and high-nitrogen treatments during spring freeze-thaw-cycle period in temperate forest would be approximately equivalent to 1% of global annual C emissions. Therefore, we show interactions between nitrogen deposition and freeze-thaw-cycle in temperate forest ecosystems are important to predict global carbon emissions and sequestrations. We anticipate our finding to be a starting point for more sophisticated prediction of soil respirations in temperate forests ecosystems. Carbon (C) cycles are increasingly paid attention under global climate change. Freeze-thaw-cycle (FTC) significantly affects soil C cycles as a crucial ecological process1–3 due to its more frequent appearance under global climate change4–6. Therefore FTC is recognized as crucial ecological processes and has received increased attention. Studying on the impacts of FTC on soil C dynamic is beneficial to the further understanding of soil C cycle and their feedback to climate change. Many previous studies have pointed out that the FTC-induced enhancement of carbon dioxide (CO2) emission was often observed7–18. Wang et al.16 showed that the ephemeral burst of CO2 occurred at the early stage of spring FTC period in a temperate forest. Song et al.15 found the high emission peaks of CO2 during FTC period in a freshwater marsh. Wang et al.17 suggested that FTC play an important role in soil CO2 emissions in a wet meadow. In addition, the CO2 emission peaks during the FTC period were also detected in some laboratory incubations10,19, which are consistent with most of the field studies. However, different conclusions have been also reported. For example, the FTC had no a significantly impact on CO2 emission in broadleaf forests or it reduced the release of CO2 in grassland20–21. The emission of CO2 from soil is one of major C exchanges between terrestrial ecosystems and the atmosphere22. With global climate change, less snowfall and warming may lead to increasing the frequency and intensity of FTC, and then may cause the increase of CO2 emission from soil to atmosphere. Sullivan et al.23 suggested that the pulses of CO2 caused by FTC are jointly driven by biological and physical factors. Several potential mechanisms have been proposed to clarify the FTC-induced enhancement of CO2 emissions: (1) burst of CO2 during the FTC period largely resulted from the release of trapped CO2 in the 1 College of Agricultural Resource and Environment, Heilongjiang University, 74 Xuefu Road, Harbin, 150080, China. School of forestry, Northeast Forestry University, 26 Hexing Road, Harbin, 150040, China. 3Institute of forestry science of Heilongjiang province, 134 Haping Road, Harbin 150081, China. 4Institute of Applied Ecology, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang, 110016, China. ∗These authors contributed equally to this work. Correspondence and requests for materials should be addressed to Q.W. (email: ) or S.H. (email: ) 2 Scientific Reports | 6:29134 | DOI: 10.1038/srep29134 1 www.nature.com/scientificreports/ winter7; (2) increased CO2 emissions may be due to enhancing microbial metabolism by substrate supply in the FTC period21; (3) increased substrates leaching from the litter layer accumulated during the winter might lead to CO2 burst24. Currently, there are still many uncertainties in the mechanisms of these increased CO2 fluxes25. The first objective of our study was to examine the impact of spring FTC on the soil CO2 emissions in the temperate forest, and then to investigate the mechanisms potentially inducing FTC period CO2 emissions. In addition, atmospheric nitrogen (N) deposition is another important factor to soil C cycle, because the cycles of soil C and N are closely coupled26–28. Some previous studies showed that simulated N addition had significantly increase release of CO2 29. Nevertheless, other studies found controversial affecting soil CO2.fluxes in terrestrial ecosystem30–31. The different responses of soil CO2 fluxes to N addition have been reported in the different ecosystem, including increases26, decreases32, and no significant differences33–34. Summary, most of the high concentration N deposition may limit CO2 release, and low concentration may promote or no changes. Several potential mechanisms have been proposed to clarify the N-induced change of CO2 emissions: (1) N inhibition of lignin degradation largely resulted from change of microbial composition35; (2) change of CO2 emissions may be due to ecological shifts in the soil microbiota under N deposition36; (3) the coupling of soil carbon and nitrogen was broken due to N deposition, which might lead to change of CO2 emission37. Although the effect of FTC on C cycles and the effect of atmospheric N deposition on C cycles have been investigated, respectively28,38,39, the effect of FTC together with atmospheric N deposition on C cycles has never been reported. We hypothesized that soil respiration (Rs) could have a special response pattern to N deposition due to the changes of soil physicochemical properties and microbial characteristic in the FTC period. The second objective of our study was to examine the impact of simulated N deposition together with spring FTC on soil CO2 fluxes in temperate forest. The major objective of this paper was to evaluate the change quantities of CO2 due to N deposition addition in FTC period in temperate forests which cover 9.7% of the earth’s continental surface40. We hypothesized that N deposition would inhibit CO2 emissions via delay burst or decrease fluxes in spring FTC period in temperate forest. In addition, previous studies did not show an understandable m (...truncated)