水分控制下的湿地沉积物氧化还原电位及其对有机碳矿化的影响

为探讨水分与氧化还原电位之间的内在关系及其对沼泽湿地有机碳分解矿化的影响,采用室内培养(25℃,155 d)实验研究了不同水分条件(24%~232%WHC)下三江平原3类湿地(泥炭沼泽、腐殖质沼泽和沼泽化草甸)沉积物氧化还原电位(Eh)变化以及有机碳的矿化特征.结果表明,不同水分条件对湿地沉积物氧化还原电位的影响有较大差异,在低于100%WHC(最大持水量)水分范围时,氧化还原电位随着水分的增加而降低,>100%WHC(至积水2 cm)时,水分含量变化对泥炭沼泽和腐殖质沼泽沉积物氧化还原电位影响作用降低.泥炭沼泽、腐殖质沼泽和沼泽化草甸沉积物有机碳矿化最适宜水分含量存在较大差异,分别为32%、48%和76%~100%WHC.湿地沉积物有机碳矿化速率与氧化还原电位之间存在二次函数关系(p<0.05),在还原态下(Eh值<300 mV),有机碳矿化速率和矿化量随氧化还原电位的升高而升高,在氧化态(Eh值>300 mV)下则逐渐降低.较低的氧化还原电位是三江平原湿地有机碳得以积累的重要原因.

Effects of Water Content on Redox Potential and Carbon Mineralization of Wetland Sediments

To better understand the effect of soil water contents on redox potential (Eh), and their impacts on C mineralization in natural wetland, sediment samples from 3 types of wetlands (fen, humus marsh and marshy meadow) in the San-jiang Plate region of North China were incubated (25℃) for 155 d under a range of reducing and oxidizing conditions by controlling water contents (varied from 24% to 232% of water holding capacity) (WHC). CO_2-C evolved during incubation was measured at different time intervals. Results showed that Eh of sediments decreased significantly as water content increased from 24% WHC (lighted moisturized) to about 100% WHC, then decreased slightly as water content increased further to a level of submersed (about 2 cm water-depths) . The accumulative amount of CO_2-C evolved from the sediments indicated that the optimum water contents for mineralization of organic C are 32% , 48% and 76%-100% WHC for sediments of fen, humus marsh, and marshy meadow, respectively. The relationship between mineralization rates and redox potentials (Eh) were well fitted with second order parabola equations (p < 0.05) . Mineralization rates and accumulative amount of organic C displayed a positive correlation with Eh up to 300 mV. However, a significant negative correlation was observed when Eh increased above 300 mV. Results demonstrated that low redox potential is the controlling factor of carbon accumulation of wetland in San-jiang Plate region.