金露梅灌丛草甸氧化亚氮排放特征及冻融交替的影响研究

摘要

在中国科学院海北高寒草甸生态系统定位研究站地区,利用密闭箱-气相色谱法对金露梅灌丛草甸群落中的丛间草地(GC)、金露梅灌丛(GG)和裸地(GL)3种斑块的氧化亚氮(N_2O)排放季节特征和冻融过程、降水事件的影响进行了初步研究.结果显示:GG年平均排放速率显著高于C.C和GL(P＜0.05),C.C与GL差异不显著(P＞0.05).3种斑块N_2O排放速率表现出明显的季节波动,生长季高于休眠季,其中GC和GG排放速率在8月出现明显峰值,2月最低;而GL的排放速率2004年最大值出现在3月,2005年在3月和8月出现了两个峰值,最低值均出现在1月.冻融交替过程中各斑块N_2O平均排放速率白天高于夜间,并且除了2005年GL斑块外,均为封冻期土壤排放速率较低,而冻融期提高.2004-07 GC和GG斑块在降雨时排放速率降低,降雨后迅速上升;而2005年时3种斑块在降雨时以及积雪融化时排放速率均大幅升高.各斑块排放速率与土壤5 cm地温呈极显著(GC和GG;P＜0.01)或显著正相关关系(GL,P＜0. 05).金露梅灌丛草甸2004年和2005年平均排放速率分别为0.043和0.046 mg/(m~2·h),是大气N_2O的一个源,粗略估算整个青藏高原高寒灌丛草甸N_2O排放的辐射强迫约为0.125 Tg CO_2,其在整个青藏高原温室气体收支中的作用不应忽略.%Emission of N_2O, an important greenhouse gas, was poorly studied in alpine ecosystems. To clarify the seasonal patterns and whether precipitation or freezing-thawing had an impact on N_2O emission, continuous monitoring was conducted in a Potentilla fruticosa shrub meadow at the Haibei Alpine Meadow Research Station of the Chinese Academic of Sciences from 2004 to 2005. Three dominant types of vegetation patches, namely shrub patch (GG), inter-shrub herbaceous patch (GC), and bare soil patch (GL), were selected and N_2O emission rate was measured by sampling in static chambers and determining with gas chromatography method. It was showed that annual average emission rate in GG were higher than that in GC and in GL in both years ( P ＜ 0. 05 ), while there was no significant difference between the latter two patches ( P ＞ 0. 05). GC and GG had similar seasonal patterns in N_2O emission. In both patches, N_2O emission rate peaked in August, and was the lowest in February. In GL, besides one peak in March and a valley value in January in both years, there was also a higher peak in August 2005.Daily average emission rate increased in GC and GG during freezing-thawing period from March to May. Emission rate was lower in GC and GG, while it was higher in GL than annual average value each in this time. During or immediately after precipitation, the emission rate was stimulated in all the patches. N_2O emission elevated gradually in snow thawing. Significantly positive correlation was found between N_2O emission rate and 5 cm soil temperature in GC and GG (P ＜0. 01 ), but not in GL Moisture Considering the proportion of area occupied by the three patches, it was calculated that the P. fruticosa shrub meadow was atmospheric N_2O source, with annual average emission rate of 0. 043 and 0. 046 mg/(m~2h) in 2004 and 2005, respectively. It was estimated that N_2O emission corresponded to radiation forcing of 0. 125 Tg carbon dioxide in the P. fruticosa shrub meadow, an un-negligible component of greenhouse gas budget of the whole Qinghai-Tibetan Plateau.