Nitrogen and water are two important factors influencing GHG (primarily CO - carbon dioxide; CH - methane, and NO - nitrous oxide) fluxes in semiarid grasslands. However, the interactive effects of nitrogen and water on GHG fluxes remain elusive. A 3-year (2010-2012) manipulative experiment was conducted to investigate the individual and interactive effects of nitrogen and water additions on GHG fluxes during growing seasons (May to September) in a semiarid grassland in Northern China. Accumulated throughout growing seasons, nitrogen input stimulated CO uptake by 3.3±1.0gCm (gN), enhanced NO emission by 1.2±0.3mgNm (gN), and decreased CH uptake by 5.2±0.9mgNm (gN); water amendment stimulated CO uptake by 0.2±0.1gCm (mmHO) and NO emission by 0.2±0.02mgNm (mmHO), decreased CH uptake by 0.3±0.1mgCm (mmHO). A synergistic effect between nitrogen and water was found on NO flux in normal year while the additive effects of nitrogen and water additions were found on CH and CO uptakes during all experiment years, and on NO emission in dry years. The nitrogen addition had stronger impacts than water amendment on stimulating CH uptake in the normal year, while water was the dominant factor affecting CH uptake in dry years. For NO emission, the N-stimulating impact was stronger in un-watered than in watered plots, and the water-stimulating impact was stronger in non-fertilized than in fertilized treatments in dry years. The interactive impacts of nitrogen and water additions on GHG fluxes advance our understanding of GHG fluxes in responses to multiple environmental factors. This data source could be valuable for validating ecosystem models in simulating GHG fluxes in a multiple factors environment.
BackgroundMowing is a widely adopted management practice for the semiarid steppe in China and affects CH4 exchange. However, the magnitude and the underlying mechanisms for CH4 uptake in response to mowing remain uncertain.Methodology/Principal FindingsIn two consecutive growing seasons, we measured the effect of mowing on CH4 uptake in a steppe community. Vegetation was mowed to 2 cm (M2), 5 cm (M5), 10 cm (M10), 15 cm (M15) above soil surface, respectively, and control was set as non-mowing (NM). Compared with control, CH4 uptake was substantially enhanced at almost all the mowing treatments except for M15 plots of 2009. CH4 uptake was significantly correlated with soil microbial biomass carbon, microbial biomass nitrogen, and soil moisture. Mowing affects CH4 uptake primarily through its effect on some biotic factors, such as net primary productivity, soil microbial C\N supply and soil microbial activities, while soil temperature and moisture were less important.Conclusions/SignificanceThis study found that mowing affects the fluxes of CH4 in the semiarid temperate steppe of north China.
Organochlorine pesticides (OCPs) have been restricted for application for about 30 years in China. Intertidal zone is a sink for anthropogenic pollutants, and to better understand the current pollution status of OCPs in China, 324 surface sediment samples collected from 14 typical intertidal zones of China were analyzed for 22 OCPs. The total concentrations of OCPs ranged from 0.051 to 4141.711 ng/g, with DDTs and HCHs being the dominant components. Seasonal variations were not significant for most intertidal zones (p > 0.05), while significant spatial variations (p < 0.05) were found among 14 intertidal zones, with the highest OCPs concentrations detected in Jiulong Jiang (JLJ). The OCPs concentrations in intertidal sediments would rarely to frequently cause adverse biological effects and DDTs were the major threat. Apart from the historical usage of technical DDT and lindane, current usage of technical DDT and HCH were also implied, especially for intertidal zones such as Beidaihe (BDH) and Yingluo Wan (YLW). PCA analysis indicated that compounds within the same type of OCPs were from similar source, while different types of OCPs were generally from different sources and not used together. Our results further indicated that OCPs together with organic particles entered into the intertidal zones mainly through river input.
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