大气CO2浓度升高对作物根际土壤氮的影响

利用FACE（Free air carbon dioxide enrichment）技术，在两种氮肥施用（低氮LN和常规氮NN）水平下，研究CO：浓度升高对水稻和小麦收获后根际和非根际土壤硝态氮、铵态氮和有机氮的影响。结果表明，相对于对照CO2浓度处理，高CO2浓度处理在显著增加作物生物量的前提下，使水稻季根际土壤硝态氮含量降低，NN水平下降低明显，小麦季变化不大，高CO2浓度处理对作物根际的影响大于非根际。高CO2浓度对土壤铵态氮含量的影响不显著，仅小幅度增加了水稻季和降低了小麦季土壤铵态氮含量，且根际降低幅度大于非根际；增加氮肥施用使土壤铵态氮含量在高CO2浓度处理增加幅度低于对照。高CO2浓度处理并没有显著增加有机氮的含量，在小麦季作物对土壤有机氮的贡献大于水稻季，且增加氮肥施用条件下根际对有机氮的贡献较大。

Effect of Elevated Atmospheric CO2 Concentration on Soil Nitrogen Around Roots of Crops

It has been well known that elevated atmospheric CO2 concentration can not only promote crops soil nitrogen uptake directly through increasing plant photosynthesis and aboveground biomass, but also influence the soil nitrogen and carbon status, indirectly through enhancing root biomass, changing root activity, root exudates and root spatial distribution. However, the effects of elevated atmospheric CO2 concentration on soil nitrogen cycle at rhizosphere and non-rhizosphere, especially under different soil fertilized nitrogen conditions, were unclear. This study aimed to reveal the effects of elevated atmospheric CO2 concentrations on the contents of soil inorganic nitrogen （nitrate- N, ammonium-N ）and organic nitrogen at rhizosphere and non-rhizosphere after crop harvest and under different nitrogen fertilizer applications for a wheat and rice rotation. The FACE （Free air carbon dioxide enrichment）systems, built at Xiaoji Town, Jiangdu City, Jiangsu Province （119042＇ 0＂ E, 32035＇5＂ N ）, provided in field two levels of CO2 concentration：ambient （370 μmol·mol^-1, as control ）and elevated （370＋200）1μmol·mol^-1, with three repeats. For each CO2 concentration level there existed two nitrogen fertilizer application rates：low （125 and 112.5 kg·hm^-2, LN ）and conventional （250 and 225 kg·hm^-2, NN ）for rice season of 2005 and for wheat season of 2004--2005, respectively. The results showed that, while significantly increased crop biomass both in rice and wheat compared with ambient CO2, elevated CO2 decreased soil nitrate-N for rice significantly, especially at NN, but no pronounced change in soil nitrate-N was found for wheat. And elevated CO2 affected soil nitrate-N at root rhizosphere more greatly than that at non-rhizosphere. There were no significant effects of elevated CO2 on soil ammonium-N for both rice and wheat, although with a slight rise trend with COs elevated for rice and a declined trend, especially at rhizosphere, for wheat. With nitrogen application rate in