土地利用方式变化是造成大气中温室气体浓度变化的主要原因之一, 但土地利用方式转变, 如林地转变为耕地过程对土壤氧化亚氮(N2O)排放的影响还缺乏系统研究.本研究于2016年7月中旬在四川盆地丘陵区将林地转变为耕地, 并按照耕地冬小麦-夏玉米轮作方式, 采用静态暗箱-气相色谱法, 对比分析了耕地翻耕不施肥(CL-T)、翻耕施肥(CL-TF)和邻近林地(CK)的土壤 N2O 排放过程特征.结果表明, 试验期间 CL-T、CL-TF土壤 N2O排放通量较 CK均显著增加(P<0.01), 且二者的 N2O排放通量在林地转变为耕地初期均有明显的排放峰.小麦季和玉米季土壤N2O排放通量[μg(N)·m-2·h-1]均值CK分别为2.52和4.60, CL-T分别为3.55和11.63, CL-TF分别为6.26和22.16, N2O排放通量玉米季显著高于小麦季.CK、CL-T和CL-TF的土壤N2O全年累积排放量[mg(N)·hm-2]分别为0.271、0.515和0.957, CL-T、CL-TF较CK分别显著增长89.8%、253.0%,说明林地转变为耕地, 紫色土N2O排放迅速增加.首先翻耕改变土壤结构并显著增加土壤无机氮含量(P<0.05),其次施肥大幅增加土壤无机氮含量导致土壤N2O的激发排放.而土壤温度和水分未发生显著改变(P>0.05), 种植作物短时间内也未显著改变土壤的N2O排放.结果表明, 林地转变为耕地激发土壤N2O排放的根本机制可能是提高了土壤有机氮矿化速率.但土地利用转变对土壤氮转化过程的影响以及进而改变土壤N2O的排放特征的机理有待进一步研究.
Land use change is one of the main reasons for changes of greenhouse gases concentration in the atmosphere. How-ever, the impacts of land use change process, such as conversion process from forestland to cropland, on soil N2O emission is still lack of a systematic study. In this study, forestland was converted into cropland in the hilly area of the Central Sichuan Basin in mid July 2016, and then planted as winter wheat-summer maize rotation from October 26, 2016 to September 15,2017. Static chamber-gas chromatographic technique were used to compare the characteristics of N2O emission from croplands, converted from forest land with tillage without fertilizer (CL-T) and with tillage and fertilizer (CL-TF), and forestland (CK). The results showed that during the experimental period, the soil N2O emission fluxes of CL-T and CL-TF both significantly increased compared to CK (P < 0.01), and there was an obvious emission peak at the beginning of land use conversion from forestland to cropland. The mean N2O emission fluxes in the wheat season and maize season were 2.52 μg(N)·m-2·h-1and 4.60 μg(N)·m-2·h-1under CK, 3.55 μg(N)·m-2·h-1and 11.63 μg(N)·m-2·h-1under CL-T, 6.26 μg(N)·m-2·h-1and 22.16 μg(N)·m-2·h-1 under CL-TF, respectively. N2O emission peak flux was significantly higher in maize season than in wheat season. The annual accumulative soil N2O emissions were 0.271 kg(N)·hm-2, 0.515 kg(N)·hm-2and 0.957 kg(N)·hm-2under CK, CL-T and CL-TF, respectively. Compared to CK, CL-T and CL-TF increased the annual accumulative soil N2O emissions by 89.8% and 253.0%, re-spectively. This indicated that land use conversion from forestland to cropland significantly induced the increase of N2O emission in purplish soil. Tillage changed soil structure and significantly increased soil inorganic nitrogen content (P < 0.05), then fertil-izer application increased soil inorganic nitrogen content sharply by a large quantity, which resulted in pulsive N2O emission. While soil temperature (5 cm) and soil moisture (WFPS) were not changed significantly (P > 0.05), and planting did not change N2O emission significantly in short time during the process of land use conversion. It was suggested that the funda-mental mechanism of stimulating N2O emission caused by land use conversion from forestland to cropland might be derived from the increase of mineralization rate of soil organic nitrogen. However, the effect of land use conversion on soil nitrogen transformation and the mechanism of changing of soil N2O emission need to be further studied.