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。

Environmental conditions greatly affect the growth of rice. To investigate the geographic differences in yield formation of single-season high-yielding hybrid rice in southern China, experiments were conducted in 2017 and 2018 in the upper and middle–lower reaches of the Yangtze River with 10–30 main locally planted high-yielding hybrid cultivars used as materials. Compared with rice planted in the middle–lower reaches of the Yangtze River, rice planted in the upper reaches has a longer tillering duration, higher accumulated temperature (≥10°C) during tillering period, but lower accumulated temperature and solar radiation from initial booting to maturity. Yield traits comparison between the upper and the middle–lower reaches of Yangtze River showed that the former had 48.1% more panicles per unit area while the latter had 46.4% more grains per panicle; the rice yield in the former was positively correlated with the seed setting rate and the dry matter accumulation before heading, while the latter was positively correlated with grains per panicle and dry matter accumulation from booting to maturity. Comparison of the same variety Tianyouhuazhan planted in different regions showed there was a significant positive correlation between panicle number and the duration of and accumulated temperature during the tillering period (r=0.982**, r=0.993**, respectively), and between grains per panicle and accumulated solar radiation during booting period (r=0.952*). In the upper reaches of the Yangtze River, more than 90% of cultivars with an yield of greater than 11 t ha^–1 had an effective panicle number of 250–340 m^–2, and there was a significant negative correlation between seed setting rate and grains per panicle; therefore, the high-yielding rice production in these regions with a long effective tillering period (>40 d) should choose varieties with moderate grains per panicle, adopt crop managements such as good fertilizer and water measures during vegetative growth period to ensure a certain number of effective panicles, and to increase the dry matter accumulation before heading. While in regions with a short effective tillering period (<20 d) but good sunshine conditions during the reproductive growth period, such as the middle–lower reaches of the Yangtze River, high-yielding rice production should choose cultivars with large panicles, adopt good water and fertilizer managements during the reproductive growth period to ensure the formation of large panicles and the increase of dry matter accumulation after heading.

Three different chlorophyll-deficient rice isogenic lines chl, fgl and pgl, and their recurrent parent zhefu802 (zf802) wereused to study effects of leaf color on photosynthesis, dry matter accumulation, yield, and quality in early season indicarice. Analysis showed that the chlorophyll (Chl.) a/b ratio of isogenic lines chl-8, pgl and fgl was 5.35, 10.00 and 15.46,respectively, among them, line fgl had higher leaf area index (LAI), higher net photosynthetic rate and higher grain-fillingrate than its recurrent parent zf802 at the later period of grain filling stage; while LAI, net photosynthetic rate and drymatter accumulated in lines chl-8 and pgl were lower than in zf802. Differences were found in the grain yield and qualityamong chlorophyll deficient isogenic lines, lines fgl, chl-8 and zf802 had similar grain yield, which was significantly higherthan that of pgl; the highest milling quality was observed in isogenic line fgl, with relatively high protein content. Thisstudy showed that isogenic line fgl would become a unique material for the development of high yield rice with high grainquality because of its slow aging process and relative steady grain-filling rate.