湿地生态系统碳汇与碳源过程的控制因子和临界条件

湿地生态系统由于其自身的结构组分特征,已成为地球表层系统中最为重要的碳汇。但是近年来对于湿地系统的不合理开发利用、降水减少等原因使其碳＂汇＂功能减弱,湿地的碳蓄积能力下降且有转变为碳＂源＂的趋势。文章从湿地生态系统的水份、植物类型、土壤厚度、微生物（底物、pH、温度、氧化还原条件）等方面总结了影响湿地碳汇/源过程的控制因子和临界交替条件。湿地水位的高低决定湿地的氧气环境,与甲烷产生量成正相关,但却与二氧化碳产生量有一定的负相关关系。湿地植物通过通气组织与根系分泌物等影响湿地碳的吸收与排放通量,湿地植株的高度、覆盖率等也是影响湿地作为碳汇与碳源的重要因素。不同深度土层由于其产甲烷菌、甲烷氧化菌等微生物活性不同导致各个土层碳吸收、排放通量的差异,通常浅层土壤中的CO2、CH4的产生率高于深层土壤。微生物的活跃程度直接影响到湿地碳的吸收与排放,影响活跃程度的因素包括湿地底物、pH、温度与氧化还原条件等。湿地底物浓度的增加会在一定程度上提高甲烷的产生率,中性或者是弱碱性环境是产甲烷菌的最适宜条件,在一定范围内温度越高,甲烷产生量越大,而温度对于二氧化碳的影响则是通过改变光合作用来实现。氧化还原电位与甲烷产生量成负相关关系,-150 mV是产甲烷菌产生甲烷的最高电位。总体上,由于湿地生态系统的复杂性和碳吸收与排放过程的复杂,以上这些因子相互作用,且在一定条件下会相互转化。最后针对如何充分发挥湿地生态系统的碳＂汇＂功能,控制湿地向碳＂源＂转化的条件措施方面进行了讨论,包括间歇灌溉、种植多年生草本植物或木本植物等来增强湿地的固碳能力。

Control factors and critical conditions between carbon sinking and sourcing of wetland ecosystem

Wetlands is the most important carbon sink as its special structure and characteristics.However the carbon sink functional of wetland has been weakened because of climate change and utilization,thus the trend that carbon sink conversion into carbon source is obvious.The control factors and critical conditions between carbon sinking and sourcing of wetland ecosystem were sum-marized from water content,plant types,soil thickness and microorganism which include substrate,pH,temperature and redox con-ditions.The wetland oxygen condition is determined by the water level of wetland.There is a positive correlation between wetland water level and methane production,meanwhile it has negative correlation with carbon dioxide.The absorption and emission of car-bon in wetland is affected by aerenchyma and root exudates of plant,but also the height and coverage of plant are important influ-ence factors.The difference of microbial activity in different depths of soil layer,which result into the difference of absorption and emission carbon.The influence factors of active degree of methanogens include substrate,pH,temperature and redox conditions.The production rate of CO2 and CH4 in shallow soil layer is higher than deep soil.Generally the increase of the substrate concentration will improve the methane generated rate and neutral or weak alkaline environment is the most suitable conditions for methanogens.of course temperature also is the influence of methane generate and carbon dioxide.It has a negative correlation relationship between redox potential and methane generating.To summarize,because of the complexity of ecosystem struceture and the process of carbon emission and absorption,it can not give a clear conclusion that wetland is carbon sink or sourse in a word.But it is clear that control factors and critical conditions will transfer in certain environment conditions,and so some measures can be taken to improve the carbon sink functional of wetland such as irrigation and planting perennial herb or woody.