大气CO_2浓度升高对农田土壤颗粒组成及其碳周转的影响

Effects of free air CO_2 enrichment (FACE) on soil particle composition and C dynamics

采集FACE（Free Air CO2 Enrichment）平台下运行3年的水稻（Oryza sativa L.）/小麦（Triticum aestivum L.）轮作土壤（0～15 cm耕作层土壤）,利用超声波分散-湿筛分法对烘干土样进行颗粒分级,分析土壤各粒级及其碳、氮的分布特征,研究大气CO2浓度升高对土壤碳周转的影响.结果表明：高浓度大气CO2条件下稻/麦轮作3年后,土壤颗粒组成较对照发生了改变,＞53 μm粒级的质量分数减小27%（p＜0.05）,约占土壤总质量20%;53～25 μm粒级的质量分数增大35%（p＜0.05）,约占土壤总质量25%;＜25 μm无明显变化,约占土壤总质量55%,三种粒级之间质量分数呈显著差异（p＜0.05）.FACE条件下,不同粒级土壤颗粒碳质量分数在两个氮水平下平均为：＞53 μm（30.60 g·kg^-1）,＜25 μm（13.08 g·kg^-1）,25～53 μm（12.85 g·kg^-1,氮质量分数分别为2.42 g·kg^-1,1.33 g·kg^-1,1.12 g·kg^-1.＞53 μm粒级的土壤颗粒碳、氮质量分数均极显著高于其它两个粒级（p＜0.001）.FACE条件下土壤总碳、氮质量分数高于对照,增幅分别为6.2%和6.7%.从各粒级土壤颗粒碳、氮质量分数变化分析,新增碳、氮主要进入＞53 μm粒级中,表明该粒级土壤颗粒对土壤碳氮循环（转化和保存）起着重要作用.该研究结果表明高浓度大气CO2条件下,稻/麦轮作农田土壤将成为大气CO2的汇,这将为预测我国未来农田土壤碳的变化趋势提供科学依据.

Soil samples, taken from 0-15 cm plow layer of riee/wheat rotation agro-ecosystem at normal nitrogen and low nitrogen levels after 3 years enriched atmospheric pCO2 （FACE-Free Air CO2 Enrichment）, are used to study the effects of elevated CO2 on soil particle composition and soil carbon turnover. The results show that the particle average weight composition of 〉53 μm, 53-25 μm and 〈25 μm particles are 20%, 25% and 55% respectively, and there are significant differences among the three particle composition （p〈0.05）; The weight composition of 〉53 μm soil particles from FACE is lower than those from Ambient （p〈0.05）, however the part of 53-25 μm soil particles is higher （p〈0.05）. The average carbon contents in the soil particles of the two nitrogen treatments are〉53 μm （ 30.60 g·kg^-1 ）, 〈25 μm （ 13.08 g·kg^-1 ）, 25-53μm （ 12.85 g·kg^-1 ）, and the nitrogen contents are 2.42 g·kg^-1, 1.33 g·kg^-1 and 1.12 g·kg^-1 respectively, the carbon and nitrogen contents in 〉53 μm soil particles arc higher than other two particles （p〈0.001）. Elevated atmospheric pCO2 increase soil C content by about 6% after 3 years＇ enriched CO2 fumigation, and C content in the 〉53 μm soil particles increase much more than the other two soil particles. These results highlight that at the future higher atmospheric pCO2 scenarios, soil at the rice/wheat rotation agro-ecosystem would be the sink of atmospheric CO2.