水分对湿地沉积物有机碳矿化的影响

Effects of water on mineralization of organic carbon in sediment from wetlands

采用室内模拟试验研究了 5个水分梯度下两种湿地沉积物有机碳的矿化特征。结果表明 ,沼泽化草甸有机碳矿化速率在培养 30 d后基本达到稳定状态。沼泽化草甸有机碳矿化适宜的含水量为 6 6 % WHC左右 ,且达到适宜含水量后 ,有机碳的矿化不受含水量增加的影响 ,矿化速率基本稳定。泥炭沼泽有机碳在 30 % WHC、5 0 % WHC两个水分梯度下 ,培养 30 d后 ,分别出现一个大约 10 0 d和 6 0 d的快速矿化期。泥炭沼泽有机碳矿化的适宜含水量为 30 % WHC左右 ,超过适宜含水量后 ,其有机碳的矿化对水分变化反应非常敏感 ,水分过多明显抑制其有机碳的矿化。水分对两种湿地有机碳矿化影响机制的差异是造成两类湿地生态系统有机碳积累量差异的主要原因之一。研究结果还表明 ,泥炭沼泽湿地积水环境的减弱将会加速其有机碳的矿化 。

Wetland ecosystems are under water-rich hydrographical environment and generally accumulate in an abundant amount of organic carbon (C) in their sediment layers. For better understanding the mechanisms in the accumulation of organic C in wetlands, the interactions between water condition and the mineralization of organic C were studied using the sediments of marshy meadow and fen from North China. The sediments were adjusted into 5 gradient of water contents: 24%～146%WHC for the marshy meadow, and 16%～104%WHC for the fen (giving both with comparable moisture conditions from lightly-moisturized to waterlogged) and incubated at 25℃ for 130 d. Results showed that the mineralization rate of organic C in the sediment from the marshy meadow at the 5 gradients of water contents decreased significantly during the early phase (11～30 d), then maintained at steady but lower levels throughout the 130 d incubation period. The accumulative amount of CO_2-C evolved from the sediment during the 130 d incubation increased significantly as water content increased from 24%WHC (lightly-moisturized) to 66%WHC, then decreased slightly as water content increased further to a level over 100%WHC (waterlogged). These results suggest that the mineralization of organic C in the sediment of the marshy meadow was not affected by high water condition. However, interactions between water condition and the mineralization of organic C in the sediment of the fen were more complicated. When incubated under a water content of 16% and 104%WHC, the mineralization rates of organic C in this sediment were generally stable throughout the 130 d incubation period. With 30% and 50% WHC, the mineralization rate increased significantly during the phase between 30 d and 90 d. The accumulative amount of CO_2-C evolved from the sediment of the fen during the 130 d incubation period increased by approximately 4 folds as water content increased from 16%WHC to 30%WHC. However, the accumulative amount of CO_2-C evolved decreased in a large extent as water content increased further. The accumulative amount of CO_2-C evolved over the 130 d at 104%WHC accounted for only 22% of that CO_2-C evolved at 30%WHC. These data propose that the mineralization of organic C in the sediment of the fen (maintained under waterlogged environment) is strongly limited by high water condition. This is suggested to be a fundamental mechanism in the large accumulation of organic C in the sediment of the fen. Data presented also propose that the disappearance of waterlogged environment in peat fen might largely enhance the mineralization of organic C.