潮汐C/N输入影响长江口湿地土壤碳周转过程的同位素验证及其分子生态机制研究

Wetland with high primary productivity and lower soil heterotrophic respiration is an important carbon sink. Due to the adsorption, absorption by plants and soil, as well as the biodegradation by soil microorganism, wetland is also considered as a pollutant purifier. .Plant litter is the main C/N input source of inland alpine wetland, but tide is another important C/N input sources for estuarine wetland. Jiuduansha wetland locates at the Yangtze River estuary, is an important ecological barrier of Shanghai. Some research found that C/N concentration in water of the upstream was higher than those of the downstream, implying Jiuduansha wetland have certain capability to intercept and purify pollutants..Preliminary statistical analysis found that the interception of the wetland to tidal C/N seemed to increase the soil respiration and carbon turnover rate. However, the environmental factors influencing soil respiration and carbon turnover of estuarine wetland are extremely complex, it is difficult to determine the real tidal C/N input intensity, influencing degree to soil respiration and mechanism with only simple statistics and correlation analysis..Therefore, the project will use stable isotope technology to quantitate the tidal C/N input intensity to the wetland soil, as well as the organic carbon sources and proportion of released CO2 from soil respiration on the basis of clarified the space pattern of soil respiration and the C\N contents in water, soil and plant of Jiuduansha wetland, thus verify the influencing degree of C/N input from tide on soil respiration and carbon turnover of wetland. .In addition, the molecular ecological mechanism about the effect of tidal C/N input on soil carbon turnover of wetland will be explored from the view of key enzyme activity, key enzyme gene transcription activity and microbial community structure. The research results will provide some new acknowledges to the relationship between pollution purification and carbon sequestration of estuarine wetland and their own premise

湿地初级生产力高，土壤异养呼吸低，是重要碳汇。由于植物\土壤的吸收、吸附和微生物的降解作用，湿地也是一个污染净化器。不同于内陆高寒湿地，潮汐是河口湿地重要的物质输入源。九段沙是长江口新生湿地，研究发现其上游水体的C/N含量高于下游，暗指其有一定的拦截、净化功能。但统计分析发现湿地对潮汐C/N的拦截似乎提升了其土壤呼吸和碳周转速率。影响河口湿地土壤呼吸和碳周转的环境因素极复杂，仅靠简单的统计关联，难以真正确定潮汐C/N输入强度及其影响湿地碳周转的效率与机制。鉴于此，课题将在阐明湿地土壤呼吸和水土植物C/N含量空间差异的基础上，结合稳定同位素技术量化潮汐C/N输入强度和湿地土壤释放CO2的来源与比例，进而验证潮汐输入对土壤碳周转的影响;并从碳周转关键酶基因与微生物结构角度解析潮汐输入影响湿地土壤碳周转的分子生态机制。研究结果对于认识河口湿地碳汇功能发挥的前提及与污染净化功能的关系具有重要意义。

湿地是地球之肾，具有较高的污染净化能力。同时湿地初级生产力高，土壤异养呼吸低，也是重要碳汇。不同于内陆高寒湿地，潮汐是河口湿地重要的物质输入源。前期研究发现，长江口湿地对潮汐中C/N的拦截作用似乎提升了其土壤呼吸和碳周转速率。但是，影响河口湿地土壤呼吸和碳周转的环境因素极其复杂，仅靠简单的统计关联，难以真正确定潮汐C/N输入强度及其影响湿地碳周转的效率与机制。鉴于此，本课题在阐明长江口湿地土壤呼吸以及潮汐、土壤环境质量空间异质性的基础上，结合标志物分析和13C同位素标记技术，量化潮汐C/N输入强度和稳定性以及湿地土壤释放CO2的来源与比例，进而验证潮汐输入对土壤碳周转的影响，并从碳周转关键酶与微生物群落结构角度解析潮汐输入影响湿地土壤碳周转的分子生态机制。结果表明，湿地上游至下游水域，TOC和N营养盐浓度逐渐降低，暗示湿地对潮汐中有机物和N营养盐的拦截效应。Spearman方程分析表明，较高的潮汐有机碳和N营养盐输入促进了有机碳的分解，从而可能影响CO2的释放和SOC的保留。正构烷烃和木质素等标志物分析结果表明，上游湿地潮汐源有机碳输入较下游更多，且可降解性较高，潮汐源有机碳相较于植物源有机碳更易降解，而芦苇凋落物较互花米草更易在土壤中保留。13C同位素标记结合微宇宙实验结果表明，潮汐中易降解的有机碳主要通过土壤呼吸以CO2的形式释放到大气中。但潮汐中来至于CO2的浮游植物有机碳仅占总有机碳的10-15%%，因此潮汐输入有机碳没有显著增加湿地土壤中的CO2当量收入，却增加了CO2输出。因此河口湿地对潮汐中有机物的拦截、吸收可能会弱化湿地的CO2汇聚功能，而潮汐N营养盐的输入可能会加剧这一过程。碳过程相关酶和微生物群落结构分析表明，易降解有机碳诱导了矿化能力较强的微生物，从而促进有机物的分解，而木质素等难降解有机物将诱导微生物的腐殖化过程，从而有利于有机物的稳定化。研究结果对于认识河口湿地碳汇功能发挥的前提及其与污染净化功能的相关性具有重要意义。