长白山阔叶红松林土壤呼吸对氮沉降增加的响应

Response of Soil Respiration to Enhanced Nitrogen Deposition in Broadleaved Korean Pine Forest in Changbai Mountains

通过原位模拟氮沉降的试验研究了长白山阔叶红松林土壤呼吸及其对氮沉降的响应。分别在6、7、8月的月初采用喷洒尿素进行施氮处理,处理水平为对照、低氮(23 kg·hm-2·a-1)、中氮(46 kg·hm-2·a-1)和高氮(69 kg·hm-2·a-1)(以氮素质量计),每月用红外分析法测定各处理水平的土壤呼吸速率3、4次。结果显示:在生长季内长白山阔叶红松林土壤呼吸有明显的季节变化,10月份最低(0.72μmol·m-2·s-1),7月份最高(2.27μmol·m-2·s-1);低、中氮处理提高了土壤呼吸速率,分别比对照高出55.4%和60.3%,高氮则降低了土壤呼吸速率,比对照低21.7%;模拟氮沉降没有改变土壤呼吸的昼夜变化趋势,其变化趋势与土壤温度一致,土壤呼吸速率与5 cm土壤温度呈显著的指数关系;模拟氮沉降增加改变了土壤呼吸对温度的敏感性,对照、低氮、中氮和高氮处理的Q10值分别为1.93、2.34、2.94和1.54。结果表明,在我国北方温带森林地区,未来氮沉降增加会促进土壤呼吸排放,并增加呼吸的温度敏感性,但过高的氮沉降会抑制土壤呼吸并降低呼吸的温度敏感性。

This study was conducted in broadleaved Korean pine forest in Changbai Mountains to explore the effects of nitrogen deposition on soil respiration.The levels of nitrogen deposition were control （CK）, low nitrogen （23 kg· hm^-2· a^-1）, medium nitrogen （46 kg· hm^-2· a^-1） and high nitrogen （69 kg· hm^-2· a^-1） by adding urea at the beginning of June , July and August since 2011.Soil respiration was measured by three to four times at mid month from May to October by using infrared gas analyzer .Soil respiration showed a strong seasonal variation with the lowest rates occurred in October （ 0.72μmol· m^-2· s^-1） and the highest rates in July （2.27μmol· m^-2· s^-1）.Low and medium nitrogen deposition promoted soil respiration significantly with the increase by 55.4%and 60.3%, respectively, while high nitrogen deposition inhibited soil respiration and the rates decreased by 21.7%.However , the diurnal pattern of soil respiration didn ’ t show significant difference between each treatment , and their trends were consistent with the seasonal course of soil temperature .The soil respiration rates of all treatments exhibited significant positive exponential relationship with soil temperature at 5 cm depth. The enhanced nitrogen deposition changed temperature sensitivity of soil respiration , and Q10 of CK, low nitrogen, medium nitrogen and high nitrogen were 1.93, 2.34, 2.94 and 1.54, respectively.The moderate nitrogen deposition can increase soil respiration rates and its temperature sensitivity , while high level of nitrogen deposition can reduce soil respiration rates and its temperature sensitivity in temperate forests in North China .