[Physiological Characteristics and Nitrogen and Phosphorus Uptake of Myriophyllum aquaticum Under High Ammonium Conditions].

Ammonium nitrogen (NH4+-N) at high concentrations is toxic to plants. In order to explore the NH4+-N tolerance of Myriophyllum aquaticum (M. aquaticum) and its ability of nitrogen (N) and phosphorus (P) uptake, this study used a nutrient solution with three NH4+-N levels (70, 210, 420 mg·L-1) to incubate M. aquaticum for 21 d. The characteristics of plant physiology and N and P uptake of M. aquaticum were measured. At NH4+-N of 70 mg·L-1, M. aquaticum grew healthily, and shoot height and biomass linearly increased with the increase incubation time. Relative shoot height and biomass of M. aquaticum were 40.56 cm and 17.82 g·hole-1 on day 21, respectively. Compared to the control with 70 mg·L-1 ammonium, malondialdehyde (MDA) content of M. aquaticum was significantly increased; chlorophyll and soluble sugar contents were also high at NH4+-N of 210 mg·L-1. M. aquaticum suffered from the NH4+-N stress. However, the stress of 210 mg·L-1 NH4+-N did not affect its normal growth and there was no significant difference in the relative growth rate of the shoot height and biomass compared with the control. At NH4+-N of 420 mg·L-1, MDA contents of M. aquaticum doubled and the shoot height and biomass growth rate were only 27.4% and 17.9% of those for 70 mg·L-1 NH4+-N, indicating that M. aquaticum was subjected to serious stress that caused unhealthy growth or even death. At three NH4+-N levels, the ranges of N and P content of M. aquaticum were 30.7-53.4 mg·g-1 and 3.8-7.7 mg·g-1, respectively, which indicated that M. aquaticum had a high uptake capacity of N and P. M. aquaticum is an ideal wetland plant that has a good application prospect for constructed wetlands in biological treatment of high-ammonia wastewater.

[Atmospheric Ammonia/Ammonium-nitrogen Concentrations and Wet and Dry Deposition Rates in a Double Rice Region in Subtropical China].

Ammonia (NH3) is the most abundant alkaline gas in the ambient air, and it is also one of the important precursors for the ammonium salts in aerosol and rainwater. Though the emission intensities of NH3 and acidic gases are high, the concentrations and deposition rates of atmospheric ammonia-nitrogen (NH3-N), particulate ammonium-nitrogen (NH4+-Np) and rainwater ammonium-nitrogen (NH4+-Nr) in double rice regions in subtropical China are still less known. In this study, atmospheric concentrations of NH3-N, NH4+-Np in PM10 and NH4+-Nr and related meteorological parameters were observed simultaneously in a typical double rice region in the subtropical hilly region of China, with the aim to clarify the characteristics and influencing factors of atmospheric NH3/NH4+-N concentrations and to quantify the wet and dry deposition rates of atmospheric NH3/NH4+-N. The results showed that the annual mean concentrations of nitrogen in NH3-N, NH4+-Np and NH4+-Nr were 5.7 µg·m-3, 12.8 µg·m-3 and 0.8 mg·L-1, respectively, and their deposition rates were 8.38, 5.61 and 9.07 kg·(hm2·a)-1, respectively. The NH3-N concentration was significantly increased after application of nitrogen fertilizer in the paddy field, and had a significant positive correlation with the air temperature. The NH4+-Np concentration did not show significant correlation with NH3-N concentration, indicating that atmospheric NH3-N concentration was not the main limiting factor for the NH4+-Np pollution in the studied region. The NH4+-Nr concentration was positively correlated with the NH4+-Np concentration but negatively correlated with precipitation. The high concentrations and deposition rates of atmospheric NH3-N/NH4+-N in the studied region indicated that the atmospheric NH3/NH4+-N pollution was serious, and atmospheric deposition of NH3/NH4+-N was an important nitrogen source in paddy fields, which should be considered in cropland nitrogen nutrient management.

[Distribution and Dynamics of Cropland Soil Organic Carbon in Jianghan Plain: A Case Study of Qianjiang City].

Taking an example of Qianjiang City in Jianghan Plain, the distribution and dynamics of soil organic carbon (SOC) in croplands was studied in present study. The cropland included both paddy field and dry land. SOC contents were analyzed by taking soil samples of topsoil (0-20 cm) in 2011 according to land uses and soil types, and then compared with the initial SOC conducted in the period of the second soil survey (1983). The results showed that SOC density and storage in 2011 was 30.50 t . hm-2and 452. 82 x 10(4) t, respectively. During the past 28 years, the cropland SOC density was decreased at a rate of 0. 10 t . (hm2.a)-1, and SOC storage was reduced by 9% with the decreasing rate of 1. 53 t.a-1. SOC density and storage in paddy field was about 1. 6 and 1. 3 times over that in dry land in the two selected periods. However, the dynamics of SOC in paddy field and dry land were quite the opposite. In paddy field, SOC was lost by 16% (52. 83 x 10(4) t), with a decreasing rate of 0. 23 t . (hm2.a)-1; whereas in dry land, SOC was increased by 5% (8. 57 x 10(4) t), with an increasing rate of 0. 05 t . (hm2.a)-1. The loss of SOC in paddy field was mainly resulted from gleyed paddy soil, which suffered a fast decrease of SOC density and accounted for 80% of SOC lost in paddy field. In addition, Hydromorphic paddy soil, accounting for 50% of the area of paddy field, tended to loss another 15% of SOC in paddy field. While in dry land, the minor SOC storage increased was dominantly attributed to grey fluvo aquic soil, which accounted for 96% of the area of dry land. Thus, the dynamics of cropland SOC in Jianghan Plain was dominantly controlled by SOC changes in paddy field. Our findings suggest that effective management should be considered to enhance the capacity of SOC accumulation and sequestration in the low-yield paddy field and the types of soils that are large in area.