土壤微生物在氮转化过程中具有很重要的作用。本实验的目的是研究根际增氧方式处理后水稻根际土壤氮转化功能基因（硝化、反硝化以及固氮基因）丰度和关键酶（脲酶、蛋白酶、氨氧化酶、硝酸还原酶以及亚硝酸还原酶）活性变化。试验设计三种增氧方式（长淹处理：又称厌氧灌溉，水稻整个生育期保持3-5 cm水层；长淹增氧处理：种植方式同长淹。水稻种植之前，在土培盆中埋入打过孔的PVC管并接到增气泵上。首次通气2小时，此后每天间隔2小时通气10分钟（由计时器控制）；干湿交替处理：又称好氧灌溉，自浅水层自然落干到土壤水势达-15 kPa 时，灌水 1~2 cm，再自然落干至土壤水势为-15 kPa，再上浅层水，如此循环），研究水稻主要生育期（分蘖期、齐穗期和成熟期）根际土壤氮转化功能基因丰度和关键酶活性变化，并分析各微生物活性指标间的相关性。结果表明，各处理水稻根际土壤氮转化功能基因丰度和关键酶活性均以齐穗期最高。增氧（长淹增氧和干湿交替处理）后水稻根际土壤硝化功能基因、固氮基因丰度增加、反硝化功能基因丰度降低；脲酶、蛋白酶和氨氧化酶活性提高，硝酸还原酶和亚硝酸还原酶活性降低，干湿交替处理尤其明显。干湿交替处理后水稻整个生育期根际土壤氨氧化古菌（AOA）和氨氧化细菌（AOB）amoA基因以及固氮基因丰度的平均值分别是长淹处理的2.87、5.75和2.97倍，反硝化功能基因nirS, nirK丰度分别比长淹处理减少73.61%和84.41%；脲酶、蛋白酶和氨氧化酶活性分别比长淹处理增加1.13、0.51和0.72倍，硝酸还原酶和亚硝酸还原酶活性分别比长淹处理减少10.30%和36.48%。相关分析结果显示：硝化功能基因和固氮基因丰度与脲酶、蛋白酶和氨氧化酶活性呈极显著正相关；反硝化功能基因丰度与硝酸还原酶活性呈极显著正相关。上述指标和土壤微生物碳、微生物氮含量均呈正相关。综上，水稻根际土壤氮转化相关的微生物活性在齐穗期最高。增氧可以提高大多数氮素转化微生物活性和土壤微生物氮含量，从而促进水稻根际土壤氮素的转化。

Soil microorganisms play important roles in nitrogen transformation.  The aim of this study was to characterize changes in the activity of nitrogen transformation enzymes and the abundance of nitrogen function genes in rhizosphere soil aerated using three different methods (continuous flooding (CF), continuous flooding and aeration (CFA), and alternate wetting and drying (AWD)).  The abundances of amoA ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), nirS, nirK, and nifH genes, and the activities of urease, protease, ammonia oxidase, nitrate reductase, and nitrite reductase were measured at the tillering (S1), heading (S2), and ripening (S3) stages.  We analyzed the relationships of the aforementioned microbial activity indices, in addition to soil microbial biomass carbon (MBC) and soil microbial biomass nitrogen (MBN), with the concentration of soil nitrate and ammonium nitrogen.  The abundance of nitrogen function genes and the activities of nitrogen invertase in rice rhizosphere soil were higher at S2 compared with S1 and S3 in all treatments.  AWD and CFA increased the abundance of amoA and nifH genes, and the activities of urease, protease, and ammonia oxidase, and decreased the abundance of nirS and nirK genes and the activities of nitrate reductase and nitrite reductase, with the effect of AWD being particularly strong.  During the entire growth period, the mean abundances of the AOA amoA, AOB amoA, and nifH genes were 2.9, 5.8, and 3.0 higher in the AWD treatment than in the CF treatment, respectively, and the activities of urease, protease, and ammonia oxidase were 1.1, 0.5, and 0.7 higher in the AWD treatment than in the CF treatment, respectively.  The abundances of the nirS and nirK genes, and the activities of nitrate reductase and nitrite reductase were 73.6, 84.8, 10.3 and 36.5% lower in the AWD treatment than in the CF treatment, respectively.  The abundances of the AOA amoA, AOB amoA, and nifH genes were significantly and positively correlated with the activities of urease, protease, and ammonia oxidase, and the abundances of the nirS and nirK genes were significantly positively correlated with the activities of nitrate reductase.  All the above indicators were positively correlated with soil MBC and MBN.  In sum, microbial activity related to nitrogen transformation in rice rhizosphere soil was highest at S2.  Aeration can effectively increase the activity of most nitrogen-converting microorganisms and MBN, and thus promote soil nitrogen transformation.