[Effect of Coupling Process of Wetting-Drying Cycles and Seasonal Temperature Increasing on Sediment Nitrogen Minerization in the Water Level Fluctuating Zone].

To reveal the effect of coupling process of wetting-drying and seasonal temperature on sediment nitrogen (N) minerization, surface sediment samples were collected from the water level fluctuating zone(WLFZ) of Pengxi River crossing two hydrological sections. The sediment samples were incubated under drying and submerging conditions at the controlled temperature. The result showed that NO3--N and sand% in the sediment of higher altitude of water level (170 m) were higher than those in low altitudes (150 and 160 m), whereas contents of TN, NH4+-N and clay% and silt% in low altitudes were much higher. Generally, Net N mineralization rate and cumulation were lower in higher altitude of water level during the drying period and submerging period. The ammonification rate decreased rapidly at the initial stage of incubation (0-7 d), and then had no obvious change, and no significant differences among altitudes was observed. The nitrification rate at low altitude decreased with incubation time, while it had only a little change at higher altitude; The nitrification contributed a higher fraction of net N mineralization than ammonification. Net N mineralization rate and its cumulation were significantly higher in the drying period than in the submerging period, while net N mineralization rate decreased with incubation time at all altitudes. Net N mineralization cumulation tended to rise first and then declined at all altitudes of the drying period, whereas it was continuously decreasing at the low water level altitude during the submerging period. Net N nitrogen mineralization rate of the drying period was positively correlate to both the sediment organic matter content and its C:N ratio, while it showed a negative correlation in the submerging period(P<0.001). Net N mineralization was sensitive to temperature increase (Q10>1) in the drying period, while it was insensitive during the submerging period of low altitude (Q10<1). Thus, the impact of temperature on Net N mineralization was relatively low in submerging period of winter and N was accumulated with low releasing rate. In contrast to winter, summer exhibited warmer and drying period, this two factors would lead to higher N mineralization rate and further induce the potential risk of eutrophication as N releasing into water body.

Four anthraquinones from Hedyotis diffusa.

A new anthraquinone has been isolated from the 95% EtOH extract of Hedyotis diffusa and characterized as 2-hydroxy-3-methoxy-6-methyl-9,10-anthraquinone (1) by extensive spectral analysis. The known compounds isolated for the first time from this plant have been identified as 2-hydroxy-3-methoxy-7-methyl-9,10-anthraquinone (2), 2-hydroxy-6-methylanthraquinone (3), and 1,3-dimethoxy-2-hydroxy-9,10-anthraquinone (4).