实验增温对西藏高原玉米田土壤呼吸的影响

摘要

青藏高原农业区正经历着明显的气候变暖,但气候变暖如何影响高寒农业生态系统碳循环目前仍不明确.土壤呼吸是第二大陆地生态系统碳通量,高寒农业生态系统土壤呼吸对气候变暖的响应的不确定性限制了气候变化背景下人类对青藏高原高寒生态系统碳循环的预测能力.2015年4月在西藏玉米田采用开顶式生长箱进行模拟增温试验,旨在探究气候变暖对土壤呼吸及其温度敏感性的影响.在2015年玉米生长季节的5-8月份,利用Li81 00土壤通量观测系统测定了6次土壤呼吸日变化(8:00-20:00),并利用HOBO微气候观测系统观测了5 cm深处的土壤温度和土壤湿度.结果表明,实验增温显著提高了5 cm深处的土壤温度(t=11.93,P=0.000),增幅为3.22℃,同时显著降低了5 cm深处的土壤含水量,降幅为0.04m3·m-3(t=-4.87,P=0.008).对照和模拟增温处理的土壤呼吸速率分别为6.79 μ.mol·m2·s-1和7.34μmol·m-2·s-1,两者间无显著差异(F=1.65,P=0.235).尽管如此,土壤呼吸仍存在着显著的日变化(F=137.66,P=0.000)和季节变异(F=54.48,P=0.000).对照和模拟增温处理的土壤呼吸温度敏感性分别为1.70和1.77,两者间也无显著差异(t=2.69,P=0.100).土壤温度解释了36％的对照处理的土壤呼吸变异,而土壤温度和土壤湿度共同解释了62％的土壤呼吸变异.因此,3.22℃的土壤增温没有显著改变土壤呼吸及其温度敏感性,这与3.22℃的土壤增温引起了土壤湿度的降低有关.%The agricultural regions on the Tibetan Plateau are experiencing obvious climatic warming,while how climatic warming will affect carbon cycling in agricultural ecosystems remains unclear.Soil respiration is the second largest carbon flux in terrestrial ecosystems.Uncertainties about the response of soil respiration in alpine croplands to climatic warming limits our ability to predict carbon cycling in alpine ecosystems on the Tibetan Plateau under future climatic change.A field warming experiment was conducted in a maize system of the Tibet in April 2015 and the objective of this study was to investigate the effect of experimental warming on soil respiration and its temperature sensitivity.Six diurnal variations of soil respiration were measured using LI8100 soil carbon flux measurement system during the period from May to August in 2015.Soil temperature and soil moisture at depth of 5 cm were also measured using HOBO microclimate measurement system.Experimental warming increased significantly soil temperature by 3.22 ℃ (t=11.93,P=0.000),but decreased significantly soil moisture by 0.04 m3·m-3 (t=4.87,P=0.008).Soil respiration under control and warming conditions was 6.79 μmol.m-2.s-1 and 7.34 μmol·m-2·s-1,respectively,and there was no significant difference of soil respiration between control and wanning treatments (F=1.65,P=0.235).However,there was significant diurnal variation (F=137.66,P=0.000) and seasonal variation (F=54.48,P=0.000) of soil respiration.Experimental warming did not affect temperature sensitivity of soil respiration (t=2.69,P=0.100) and temperature sensitivity of soil respiration in control and warming treatments was 1.70 and 1.77,respectively.Soil temperature explained 36％ variation of soil respiration in control plots,while soil temperature and soil moisture together explained 62％ variation of soil respiration.Therefore,3.22 ℃ increase in soil temperature did not affect soil respiration and its temperature sensitivity,which was correlated with the decline in soil moisture caused by experimental warming.