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Permanently flooded rice fields, a special kind of all year-round flooded rice fields in China, where the crop system is summer rice ( Oryza sativa ‘Q You 6′) with winter fallow, contribute to both CH 4 and N 2 O emissions. To investigate their CH 4 and N 2 O emissions over a whole year (November 2009 to October 2010) and responses to long-term tillage-cropping systems, four treatments after the conversion of such rice fields were examined: conventional tillage with a single summer rice and floodwater winter fallow (CTRF) or drained winter rapeseed ( Brassica napus ‘W You 25′) (CTRR), no-tillage narrow- or wide-ridge with a rice and rapeseed rotation (NTNRR or NTWRR). Results showed that CTRF emitted the highest CH 4 owing to permanently flooding water layer and higher soil organic carbon concentrations. Compared to CTRF, CH 4 emissions under other three tillage-cropping systems were decreased not only in the winter season but also in the rice-growing season. In contrast, N 2 O emissions over a whole one-year rice-rapeseed rotation cycle were almost equivalent to each other under these four tillage-cropping systems. Also compared to CTRR, the two no-tillage-cropping systems tended to enhance CH 4 while decrease N 2 O emissions, though with insignificant effects. The annual cumulative emissions of CH 4 and N 2 O were highest under CTRF (1.07 ± 0.20 kg CO 2 -eq ha −1 kg −1 yield) and significantly decreased under CTRR, NTNRR and NTWRR (0.59 ± 0.10, 0.67 ± 0.05 and 0.58 ± 0.09 kg CO 2 -eq ha −1 kg −1 yield, respectively), indicating that the summer rice-winter rapeseed rotation system, irrespective of tillage management, rather than the summer rice-winter fallow system, had achieved the objective of higher yields with less greenhouse gas emissions. These results demonstrate that the no-tillage wide-ridge with a rice and rapeseed rotation (NTWRR) is the most efficient management in terms of decreasing CH 4 and N 2 O emissions in Southwest China.

In order to understand the changes of dissolved carbon and dissolved nitrogen in the water of Three Gorges Reservoir,this research was carried out once a week by the bank of Yangtze River in Fuling beach from March 2011 to August 2012,and the variation characteristics of dissolved C,N composition and their source were analyzed.The results showed that the concentration of DOC ranged from 0.64 mg·L

Taking a typical drawdown area located in Wangjiagou of the Three Gorges Reservoir as the study object, four elevations 180,175,165 and 155 m were selected to explore the effect of water level change on soil microbial biomass carbon (SMBC) and microbial biomass nitrogen (SMBN). Wherein, 175,165 and 155 m elevations located in the fluctuating zone, manifested as short, medium and long-term flooding, respectively; 180 m was used as the control, located on the land and never flooded. Sampling depth in soil samples was 0-20 cm, collected once a week. The results indicated that, soil organic carbon (SOC) and total nitrogen (TN) contents at 180 m had no obvious seasonal changes, while they showed remarkable seasonal trends at 175m, which in spring and summer were significantly higher than in autumn and winter; SMBC and SMBN contents and their allocation ratio at four elevations were similar and had significant seasonal fluctuation, which were highest in autumn and lowest in summer at each elevation, indicating that in drawdown area the microbial activity and turnover rate of soil organic carbon and nitrogen were limited by the high-temperature and low-humidity soil environment in summer. Data analysis showed that, compared with the 180 m elevation, contents of SOC, TN, SMBC and microbial quotient, SMBN and its allocation proportion showed varying degrees of increase, while contents of these indexes were significantly lower than control except SMBN and its allocation proportion, meaning that compared with 180 m short and medium-term flooding was conducive to improve soil carbon, nitrogen and their turnover rate and microbial biomass, however, contents of soil carbon and nitrogen and microbial biomass carbon were significantly restricted at 155 m as soil was subjected to flooding stress, meanwhile the turnover rate of SOC was reduced. Correlation analysis implied that SMBC and SMBN had very significant negative correlation with temperature at 5 cm soil depth and pH, meaning that the two environmental factors had a strong effect on soil microbial biomass.

Five levels (180 m, 175 m, 165 m, 155 m, and 140 m) in a typical drawdown area in Wangjiagou in the Three Gorges Reservoir were selected to study CH

Three heights (180 m, 175 m and 155 m) located in a typical drawdown area in Wangjiagou of the Three Gorges Reservoir were selected for studying the N