Supported by the National Natural Science Foundation of China (Nos. 41471212, 31470558, and 31290221), the National Key Research and Development Program (No.2012CB417103), and the Bingwei’s Funds for Young Talents of Chinese Academy of Sciences (No.2011RC202)
中国亚热带人工林处于全球氮沉降高值区，土壤氮素相对富集，土壤氧化亚氮（N2O）产生与排放对外源性氮素输入响应敏感。然而，现有氮沉降模拟控制实验多采用单一氮肥类型，没有原位区分氧化态氮与还原态氮素影响的差异。以千烟洲亚热带湿地松林为研究对象，增氮控制实验采用随机区组设计，包括2种形态（NO3-、NH4+）和3个施氮水平（0、40、120 kg hm-2 a-1）。利用静态箱—气相色谱法高频（8次 月-1）测定土壤N2O净交换通量以及温度、水分、溶解性氮含量等相关环境变量，分析土壤N2O通量对外源性氮素输入的响应特征及主控因子。结果表明：施氮不影响亚热带人工林土壤温度和水分，显著增加了土壤NO3--N、NH4+-N和总溶解性氮（TDN）的含量，对溶解性有机氮（DON）含量无显著影响。施氮显著促进亚热带人工林土壤N2O排放，增幅为378%~847%，施加NH4Cl的促进效应显著高于Na NO3。土壤N2O通量与10 cm土壤温度、10 cm土壤体积含水量呈正相关，土壤N2O通量的变化量与土壤无机氮含量的变化量呈正相关。上述研究结果表明，虽然水热因子驱动着亚热带人工林土壤N2O的排放，但是氮素富集条件下土壤N2O的增加主要由底物可利用性的变化所致，并且还原态NH4+的促进效应显著高于氧化态NO3-。
Human activities, such as combustion of fossil fuel, production and utilization of chemical fertilizers, intensification of livestock husbandry, etc. have caused atmospheric nitrogen depositionon the globe to increaseby 3 times, which significantly alters nitrogen recycling in forest ecosystems. Subtropical plantations in China are located in the center of the region very high in atmospheric nitrogen deposition on the globe, where the soils, relatively enriched with nitrogen, are very sensitive to input of extraneous nitrogen, in production and emission of soil nitrous oxide (N2O). However, in the past, the experiments to simulate N deposition used to have only one type of N fertilizer such as NH4 NO3 or urea as N source, without taking into account the difference in in-situ effect between oxidized N and reduced N. In this study, a plantation of pinus elliottii at the Qianyanzhou Subtropical Experiment Station, Chinese Academy of Sciences, was selected as an object in an experiment on controlled N addition. This experiment was designed to have two forms of N fertilizers (NH4Cl and NaN3O) and three N application rates (0, 40 and 120 kg hm-2 a-1) and laid out in plot randomly. Soil-atmospheric N2O exchanging fluxes, were measured eight times per month using the static chamber-gas chromatography method, and simultaneously, soil temperature and moisture at 0～10 cm depth, dissolved N concentrations (NO3--N, NH4+-N, total dissolved N (TDN), and dissolved organic N (DON)) at 0～15 cm depth were determined for analysis of how the N2O exchanging flux responded to input of extraneous N and its main affecting factors. Results show that N addition did not affect soil temperature and soil moisture in the subtropical plantation, but did increase significantly soil NO3--N, NH4+-N and TDN contents, except for soil DON content, of which the potential mechanisms included preferential absorption of NH4+-N by plants, fixation of NH4+-N by soil organic matter/ minerals, and assimilation of inorganic by plants and soil microbes. Also, N addition significantly promoted soil N2O emission in the subtropical plantation or by 378%~ 847%; and the effect was higher in plots applied with NH4Cl than in plots applied with Na NO3. Moreover, soil N2O flux was found to be positively and significantly related to soil temperature and soil moisture at 0-10cm depth, which indicates that the hydrothermal factors propelled soil N2O emission in the subtropical plantation. Also, the change in soil N2O flux (Δsoil N2O fluxes, the difference between N treatment and control) was significantly and positively related to that in soil NH4+-N and NO3--N contents (Δsoil inorganic N contents), and the relationships could well be fitted with linear and exponential growth equations, respectively. The findings of the study indicate that the increase in soilN2O content in N-enriched soils is mainly attributed to changes in substrates for nitrifier and denitrifier communities, and hint that soil N2O emission in the subtropical plantations, South China, is very sesitive to input of extraneous N, and more to reduced NH4+ than to oxidized NO3-. The sensitivity is higher than the mean of the globe. Therefore, it is advisable to address reduced NH4+ and oxidized NO3 separately, in assessing influence of atmospheric N deposition on carbon and N recycling and C budget in future studies. Unfortunately, the failure of this study to determine activities of soil nitrifier and denitrifier communities made it hard to assess relative contributions of various processes, separately, to soil N2O flux. For future studies, it is recommended to apply 15N tracer and molecular microbiology in in-depth analysis of the relationships between soil N transformation processes and soil N2O flux, and coupling effects of key microbial functional groups and soil N transformation and emission processes.
王 磊,程淑兰,方华军,于贵瑞,党旭升,李晓玉,司高月,耿 静,何 舜.外源性NH4+和NO3-输入对亚热带人工林土壤N2O排放的影响[J].土壤学报,2016,53(3):724-734. DOI:10.11766/trxb201507280291 WANG Lei, CHENG Shulan, FANG Huajun, YU Guirui, DANG Xusheng, LI Xiaoyu, SI Gaoyue, GENG Jing, HE Shun. Effects of Inputs of Extraneous NH4+and NO3- on Soil Nitrous Oxide Emission in Subtropical Plantation, South China[J]. Acta Pedologica Sinica,2016,53(3):724-734.复制