稻田冬闲期CO_2气体排放的观测研究

CO_2 fluxes of non-cropping wintry paddy field in subtropical region

亚热带红壤稻作区是华中地区的主要生态系统类型,在生态、经济以及社会效益方面都起着非常重要的作用。为了解这一生态区域的碳循环过程的因素和机理,同时为进一步解释农田碳循环过程对温室气体CO2的影响提供科学依据,采用静态箱式法对亚热带红壤性稻田长达约5个月的冬季休闲期(2005年11月—2006年4月)CO2气体排放通量进行了田间原位观测,并结合同步气象资料进行了分析。结果表明:亚热带红壤性稻田冬闲期CO2通量与近地面CO2体积分数的季节变化基本同步,与地面稻田生态系统的CO2通量对大气CO2体积分数的影响60%;CO2通量日变化规律基本为昼吸夜排:白天表现为田间杂草光合作用的结果,受光合有效辐射的影响,CO2通量与光合有效辐射的关系符合对数曲线,相关性达到显著水平;夜晚则以呼吸过程为主,主要受温度的影响,CO2通量与温度呈线性关系,其中气温和5cm地温最适宜用作于描述夜间CO2通量对温度变化的响应的指标。亚热带红壤性稻田生态系统在149d的休闲期内从大气中累积吸碳量(以CO2计)约4.03t·hm-2,表现为大气的碳汇。

As a main type of ecosystem, subtropical red paddy region represents an important economic and ecological resource at mid-china. This ecosystem has a wintry fallow period that can last nearly five months. The CO2 fluxes during this long period likely play an important role in determining annual fluxes in the ecosystem, however, few studies have measured continuous CO2 fluxes in red soil paddy ecosystem during the winter. The objective of our study was to obtain measurement data of CO2 fluxes during winter at representative subtropical red paddy region and to study their relationships to meteorological factors. Measurements of CO2 fluxes were obtained using closed static chamber technique once two weeks during the winter at Taoyuan Station of Agro-ecosystem Research, Chinese Academy of Science. Average daily ecosystem respiration during the winter period （from November I to April 3） was 2.58 g.m^-2-d^-1 and the result shows that： （1）CO2 concentration near the ground and CO2 fluxes were changing in the same pace, and the seasonal dynamics of CO2 fluxes appeared marked linear relationships with air temperature. （2）The daily dynamics of CO2 fluxes of non-cropping wintry paddy field in subtropical region is： during the daytime, affected by Photosynthesis Available Radiation （PAR）, paddy ecosystem fixed CO2 from atmosphere, there was a very conspicuously logarithmic relationship between PAR and CO2 fluxes; during the night, respiration progress of weed and soil emitted CO2 into atmosphere, and temperature was the main influence factor. It proved that air temperature （Ta） and soil temperature under 5 cm （Tgs） were the most suitable index for describing the linear relationship between CO2 fluxes and temperature. （3）During the fallow period （149 d）, the paddy ecosystem fixed 4.03 t CO2·hm^-2 from atmosphere . Based on this primary testing of empirical flux models, additional research will be required to develop mathematical models that reliably predict winter CO2 effluxes across a wide range of subtropical region.