鄱阳湖湿地土壤有机碳分解的温度敏感性研究

Temperature sensitivity of soil organic carbon decomposition is the key parameter for predicting soil carbon dynamics and feedbacks to climate change. However, there is no agreement on whether various soil organic carbon components differed in their temperature sensitivities, and case study of wetland is not available in particular. In this study, soils will be sampled along water table gradient in the typical Poyang Lake wetland where the vegetations are covered by submerged to emerged plants. Subsequently,the soil samples will be taken to the laboratory for incubation with two temperatures (20℃ and 30℃) multiplying four moisture (30%, 60%, 100% WHC and 2 cm water depth) treatments. Based on the soil incubation experiment and molecular biology technology T-RFLP(Terminal Restriction Fragment Length Polymorphism),temperature sensitivity of soil organic carbon decomposition and its control factors will be studied. The objectives of this study were:1)to clarify the difference in temperature sensitivity between labile and recalcitrant organic carbon, as well as the mechanism.2)to discuss the influences of variation in wetland water regime and vegetation on the temperature sensitivity of organic carbon decomposition. On the one hand, the results of this study will not only help to reduce the uncertainty on the knowledge of temperature sensitivity of organic carbon decomposition, but provide useful data for the improvement of regional or global carbon cycle models. On the other hand, the results will play important role in understanding and predicting response of carbon stock in subtropical lake wetlands to climate change and its feedbacks.

有机碳分解的温度敏感性是模型预测土壤碳库变化及其对气候变暖反馈的关键参数，不同有机碳组分之间是否存在温度敏感性差异迄今没有一致结论，更缺乏湿地土壤例证。本项目拟选择鄱阳湖湿地典型区，沿水位梯度采集挺水植物区、湿生植物区、沉水植物区以及深水无植物区土壤样品，通过设置2个温度（20℃、30℃）×4个水分（30%WHC、60%WHC、100%WHC、淹水2cm）处理组合，进行室内培养试验，并结合分子生物学技术(T-RFLP),开展土壤有机碳分解的温度敏感性及影响因子研究，以阐明鄱阳湖湿地土壤易分解与难分解有机碳的温度敏感性差异及机理；探讨湿地水分与植被变化对土壤有机碳分解的温度敏感性影响。项目研究结果一方面有助于降低当前对土壤有机碳分解的温度敏感性认知的不确定性，为区域或全球碳循环模型的完善与发展提供数据支持；另一方面对于理解和预测亚热带湖泊湿地土壤碳库对气候变化的响应与反馈具有重要意义。

有机碳分解的温度敏感性是模型预测土壤碳库变化及其对气候变暖反馈的关键参数，不同有机碳组分之间是否存在温度敏感性差异迄今没有一致结论，更缺乏湿地土壤例证。本项目选择鄱阳湖湿地典型区，沿水位梯度采集南荻、灰化苔草、黑藻群落土壤0-10cm、10-30cm样品，通过设置2个温度×4个水分处理组合，进行室内培养，以阐明鄱阳湖湿地土壤易分解与难分解有机碳的温度敏感性差异及机理；探讨湿地水分与植被变化对土壤有机碳分解的温度敏感性影响。结果表明：(1)南荻、灰化苔草和黑藻群落土壤易分解有机碳Q10值变化范围分别为：1.33~2.57、1.65~2.82、1.07~1.94；难分解或相对难分解有机碳Q10值变化范围分别为：2.21~5.84、2.55~6.59、2.66~3.93；3种群落土壤各温度、水分处理均表现为难分解或者相对难分解有机碳的温度敏感性高于易分解有机碳。(2)土壤水分未显著影响有机碳分解的温度敏感性，亦未发现本研究所代表的鄱阳湖典型湿地土壤有机碳分解的温度敏感性高于文献报道的陆地土壤。(3)甲烷释放消耗的有机碳在本研究各处理中均可以忽略不计，未明显影响有机碳分解过程中的温度敏感性。(4)黑藻群落0-10cm未淹水处理土壤有机碳分解的温度敏感性随着有机碳分解比例的增加而增加，但当初始有机碳消耗超过14%后，有机碳的温度敏感性开始下降，表明难分解有机碳部分仍然存在不同的温度敏感性，Q10并非随有机碳的难分解程度呈线性增加关系。(5)随着土壤易分解有机碳逐渐消耗完，难分解有机碳比例增加，土壤微生物量碳、氮呈现下降趋势，微生物群落中优势微生物发生转移，微生物多样性发生变化，这些都在一定程度上解释了有机碳分解过程中分解速率不断下降，以及不同组分有机碳具有不同的温度敏感性。本研究结果进一步丰富了对湿地土壤有机碳分解的温度敏感性认识，将为区域或全球碳循环模型的完善与发展提供数据支持；另一方面对于理解和预测亚热带湖泊湿地土壤碳库对气候变化的响应与反馈具有参考价值。