No abstract

Few investigations have been made on the impact of elevated ozone (O 3 ) concentration on methane (CH 4 ) emission from rice paddies. Using open-top chambers in situ with different O 3 treatments, CH 4 emissions were measured in a rice paddy in Yangtze River Delta, China in 2007 and 2008. There were four treatments applied: charcoal-filtered air (CF), nonfiltered air (NF), and charcoal-filtered air with different O 3 additions (O 3 -1 and O 3 -2). The mean O 3 concentrations during the O 3 fumigation were 19.7, 22.6, 69.6 and 118.6 ppb in 2007 and 7.0, 17.4, 82.2 and 138.3 ppb in 2008 for treatments CF, NF, O 3 -1 and O 3 -2, respectively. The rice yields, as compared with CF, were reduced by 32.8% and 37.1%, 58.3% and 52.1% in treatments O 3 -1 and O 3 -2 in 2007 and 2008, respectively. The diurnal patterns of CH 4 emission varied temporally with treatments and there was inconsistence in diurnal variations in CH 4 emissions from the paddy field. The daily mean CH 4 emissions were significantly lower in treatments O 3 -1 and O 3 -2 than those in treatments CF and NF. Compared with CF treatment, CH 4 emissions from the paddy field were decreased to 46.5% and 38.3%, 50.6% and 46.8% under treatments O 3 -1 and O 3 -2 in the whole growing seasons of 2007 and 2008, respectively. The seasonal mean CH 4 emissions were negatively related with AOT40 (accumulative O 3 concentration above 40 ppb; Po0.01 in both years), but positively related to the relative rice yield (reference to CF; Po0.01 in 2007 and Po0.001 in 2008), aboveground biomass (Po0.01 in both years) and underground biomass (Po0.01 in 2007 and Po0.05 in 2008). The decreased CH 4 emission from the rice paddy due to an increased O 3 exposure might partially mitigate the global warming potential induced by soil carbon loss under elevated O 3 concentrations.

No abstract

No abstract

a b s t r a c tThe effects of a continuing rise of ambient ozone on crop yield will seriously threaten food security in China. In the Yangtze River Delta, a rapidly developing and seriously air polluted region in China, innovative open-top chambers have been established to fumigate winter wheat and rice in situ with elevated O 3 . Five years of study have shown that the yields of wheat and rice decreased with increasing O 3 concentration. There were significant relationships between the relative yield and AOT40 (accumulated hourly O 3 concentration over 40 ppb) for both winter wheat and rice. Winter wheat was more sensitive to O 3 than rice. O 3 -induced yield declines were attributed primarily to 1000-grain weight and harvest index for winter wheat, and attributed primarily to grain number per panicle and harvest index for rice. Control of ambient O 3 pollution and breeding of O 3 tolerant crops are urgent to guarantee food security in China.

Rapid urbanization has resulted in the permanent conversion of large areas of cropland and natural vegetation to impervious surfaces and therefore greatly modified land surface properties and land‐atmosphere interactions. This study sought to examine the urbanization process using Landsat images from 2001 to 2010 in metropolitan JingjinTang (JJT), a rapidly expanding urban cluster in northern China. We aggregated the original results of land use data as fractional cover information in 1 km and 10 km grids. Annual and seasonal land surface temperatures (LSTs) were processed from Moderate Resolution Imaging Spectroradiometer products. We used moving window and gradient analysis methods to examine the differences in LST between urban and other land types, further identifying LST increases in gradients of urbanization levels. Urban extent increased by 1.6 times, and approximately 45% newly developed areas were converted from croplands during this process. Emerging urban land in JJT has caused approximately 0.85 ± 0.68°C warming in terms of annual mean LST, and the greatest warming occurred in the summer. An increase in urban land of 10% in a 1 km grid in JJT would cause approximately a 0.21°C increase in annual LST. Urbanization also led to increases in daytime LSTs and nighttime LSTs by approximately 1.03 ± 1.38°C and 0.78 ± 1.02°C, respectively. The warming trend induced by urbanization exhibits clear seasonal and diurnal differences, and this warming trend is most likely caused by the cumulative effects of changes in land properties, radiation storage, and anthropogenic heat release by urbanization.

[1] Methane (CH 4 ) emissions from the drawdown area of the Three Gorges Reservoir (TGR) have not been thoroughly investigated even though the drawdown area encompasses one third of the reservoir surface. In this study, CH 4 emissions from different land uses were measured in the TGR drawdown area. The average diffusive CH 4 emissions were 2.61, 0.19, 0.18, and 0.12 mg CH 4 m À2 h À1 in rice paddies, fallow lands, deforested lands, and croplands, respectively, and were positively related to the duration of the inundated season among the latter three land uses. On average the drawdown areas studied here (except rice paddies) were sources in the inundated season (0.22 AE 0.26 mg CH 4 m À2 h À1) and a sink in the drained season (À0.008 AE 0.035 mg CH 4 m À2 h À1). The water level was the dominant factor that controlled whether the drawdown area was either inundated or drained, which in turn determined whether the drawdown area was a source or sink of CH 4 emissions. The average diffusive CH 4 emissions from the fallow lands, croplands, and deforested lands increased as the distance from the dam increased from Zigui (0. ), which could reflect different sediment characteristics and water velocities. The total CH 4 emission from the drawdown area was estimated to range from 1033.5 to 1333.9 Mg CH 4 yr À1 , which would account for 42-54% of the total CH 4 emissions from the water surface of TGR.

a b s t r a c tWith the open-top chambers (OTCs) in situ in Yangtze River Delta, China in 2007 and 2008, the effects of elevated O 3 exposure on nutrient elements and quality of winter wheat and rice grain were investigated. Grain yield per plant of winter wheat and rice declined in both years. The N and S concentrations increased under elevated O 3 exposure in both years and CeN ratios decreased significantly. The concentrations of K, Ca, Mg, P, Mn, Cu and Zn in winter wheat and the concentrations of Mg, K, Mn and Cu in rice increased. The concentrations of protein, amino acid and lysine in winter wheat and rice increased and the concentration of amylose decreased. The increase in the nutrient concentration was less than the reduction of grain yield in both winter wheat and rice, and, hence, the absolute amount of the nutrients was reduced by elevated O 3 .