中文摘要：

以水稻田田间定位试验为研究对象，利用三维荧光光谱技术（3D EEMs）和454测序技术，采集4个施磷水平（0、30、60、90 kg hm-2a-1）土壤，测定其有机碳矿化、溶解有机碳（DOC）组成和结构特征及细菌群落结构和丰度的变化。结果显示：水田施磷增加了土壤速效磷（Olsen-P），从而提高了土壤DOC含量，加速了有机碳的矿化速率和累积矿化量。3D EEMs 结果表明，施磷分别显著增加了荧光指数和鲜度指数值1%～10%和3%～21%，而降低了腐殖化指数，且与土壤生化性质（Olsen-P、DOC和β-葡萄糖苷酶）具有显著相关性。说明施磷通过提高Olsen-P，促进了微生物源DOC的生成，同时降低了DOC的芳香化程度、分子量及腐殖化程度，从而提高了DOC生物可降解性。同时，施磷提高了细菌群落的丰度和多样性，特别是磷诱导了多种具有碳降解功能细菌的增加，从而加速了复杂有机碳的降解和甲烷氧化。此外，主成分分析表明稻田磷素施用量在30～60 kg hm-2a-1时对土壤有机碳矿化及细菌群落多样性的提高作用最为明显。因此，适度施磷能显著提高涉碳降解微生物的活性，从而提高DOC的生物可降解性，加速有机碳的矿化速率，促进稻田土壤有机碳循环。

英文摘要：

Soil dissolved organic carbon （DOC） is an important fraction in the global carbon cycle and is critical to soil biogeochemical processes related to soil fertility and climate change. Soil bacteria play an important role in controlling soil DOC dynamics. To determine effects of phosphorus （P） fertilization rate on paddy field soil mineralization of the soil organic carbon, DOC structural complexity and bacterial community structures, a stationary field experiment, designed to have four P application rates, i.e. 0, 30, 60 and 90 kg hm-2a-1 of superphosphate, was carried out in a paddy field, and lab analysis was performed with the 3D EEMs and 454 pyrosequencing techniques. Results show that higher P application rate raised the content of soil readily available phosphorus （Olsen-P）, thus increasing the content of soil DOC, and DOC mineralization rate and accumulative mineralization as well. Analysis with the 3D EEMs demonstrates that P input increased fluorescence index and β/α index of the DOC by 1%~10% and 3%-21%, respectively, but decreased its humification index, which were significantly related to soil biochemical properties （Olsen-P, DOC and β-glucosidase）. The results also indicate that P application increased the content of Olsen P, stimulated formation of microbe-derived DOC and meanwhile decreased the aromatization degree, molecular weight and humification degree of the DOC, thus improving the biodegradability of the DOC. P input also increased the abundance and diversity of microbial communities, and in particular, induced growth of a variety of carbon-degrading bacteria , thus speeding up degradation of complicated organic carbon and oxidation of methane. Besides, principal component analysis shows that the effect of P fertilization on mineralization of SOC and diversity of bacterial communities was the most significant when P 30～60 kg hm-2a-1 was applied. It is, therefore, assumed that a proper rate of P applied may significantly stimulate the activity of C-degradation-related micro