稻田CO2排放对大气CO2浓度升高的响应

CO_2 Emission in Response to Atmospheric CO_2 Enrichment in a Rice Paddy Field

利用FACE(free-air carbon dioxide enrichment)平台,采用静态暗箱-气相色谱法,研究了大气CO2浓度升高对稻田土壤CO2通过土壤-大气(土气)和植被-大气(植气)界面排放的影响。在整个水稻生长季中,土气界面CO2排放通量与土壤表面水层深度指数负相关,且在中期烤田和收获前排水阶段出现较大值;而植气界面CO2排放通量与根系生物量的变化趋势基本一致。在低氮(N 125 kg/hm2)和常氮(N 250 kg/hm2)水平上,高浓度CO2(对照大气CO2浓度+200μmol/mol)有提高水稻生物量、降低土气和植气界面CO2累积排放量的趋势。在水稻的拔节、抽穗和成熟期,较高的施氮量显著增加水稻地上部分生物量,促进植气界面CO2的排放。研究结果表明,未来大气CO2浓度升高的环境下,稻田生态系统有增加CO2的固定(增加水稻生物量),减少CO2的排放(土气和植气界面CO2的排放)的趋势,可能发挥着碳汇的作用。

A static opaque sampling-gas chromatograph measuring metbod was used to investigate the effect of elevated CO2 on soil CO2 emission through soil-atmosphere （SA） and plant-atmosphere （PA） interfaces in rice growing season under FACE system. Through entire rice growing season, soil CO2 flux through SA interface exponentially correlated with the water depth on soil surface and peaked in the periods of mid-season and pre-harvest drainages, whereas soil CO2 through PA interface related to rice root biomass. Elevated CO2 （ambient CO2 ＋ 200 μmol/mol） had a potential to increase rice biomass and decrease soil CO2 emission through SA and PA interfaces under low-nitrogen （N 125 kg/hm^2） and normal-nitrogen （N 250 kg/hm^2） le.vels. Higher nitrogen supply significantly enhanced rice aboveground biomass at jointing, heading and maturity stages, which promoted CO2 emission through PA interface. The results indicated that the rice paddy ecosystem probably plays a carbon sink role as a result of an increase in CO2 fixation by enhancing rice biomass and a decrease in CO2 emission through SA and PA interfaces under elevated CO2 condition.