大气CO_2浓度增高对农田土壤硝化活性的影响

Effects of elevated atmospheric CO_2 concentration on soil nitrification activities

利用中国唯一的FACE(Free-AirCarbondioxideEnrichment,开放式空气CO2浓度增高)平台,研究大气CO2浓度增高对农田土壤硝化活性的影响。位于无锡的中国稻麦轮作农田生态系统FACE试验平台于2001年6月开始运行,设有FACE与Ambient(普通空气对照)2个处理,FACE区CO2浓度比Ambient区高200μmol·mol-1,每个处理含低氮与常氮2个氮肥水平。在轮作水稻和小麦各3季之后,发现大气CO2浓度增高下,常氮水平上土壤的NO3--N质量分数降低,NH4+-N质量分数增高;而低氮水平上土壤的NO3--N质量分数增高,NH4+-N质量分数没有显著差异。然后分别在土壤样品中加入NH4+-N,好气培养42d后通过测定土壤中的NO3--N、NO2--N总质量分数来研究土壤的硝化活性。结果显示,不管在CO2浓度增高下还是对照条件下,增加氮肥施用量均增强了土壤的硝化活性;且与对照相比,大气CO2浓度增高在常氮水平上降低了土壤的硝化活性,在低氮水平上却增强了土壤的硝化活性,说明大气CO2浓度增高对农田土壤硝化活性的影响与N肥供应水平有关。

A FACE (Free-Air Carbon dioxide Enrichment) system was used to investigate the effects of elevated atmospheric CO2 concentration on soil nitrification activities. The FACE system was conducted under rice/wheat rotation from June, 2001 at Wuxi, China, and the CO2 concentration in the FACE is about 200 μmol·mol-1 higher than that in the ambient. Two N application levels (normal and low N) were included under both FACE and the ambient conditions. After three seasons of rice and three seasons of wheat, the soils were collected for mineral N and nitrification activity determinations. We observed that, under normal N level, the soils in the elevated CO2 concentration had lower nitrate content but higher ammonium content than those in the ambient, while un-der low N level the nitrate content was higher in the elevated CO2 concentration, and the ammonium contents were not significant different in two CO2 concentrations. Soil nitrification activities increased with increasing N application rate under both elevated CO2 concentration and the ambient conditions. The elevated CO2 concentration decreased soil nitrification activity at normal N level while increased at low N level, suggesting that N application level was critical in the effect of elevated atmospheric CO2 concentra-tion on soil nitrification activities.