小叶章湿地表土水溶性有机碳季节动态变化及影响因素分析

Seasonal dynamics of dissolved organic carbon and its impact factors in the Doyeuxia augustifolia marsh soil

湿地土壤及水体中水溶性有机碳(DOC)的产生、迁移与转化对湿地土壤碳通量具有重要的影响.然而,目前对沼泽湿地土壤DOC动态变化及影响因素的研究报道还比较少.对小叶章湿地表土DOC季节动态变化及影响因素进行了研究.结果表明,生长季内,表土DOC含量为373.9～443.7 mg·kg-1,平均值为414.6 mg·kg-1,变异系数为7.7%(P＜0.0001).小叶章湿地表土DOC含量有明显的季节性动态变化.5月份表土DOC含量较高,6～7月份DOC含量下降,7月份达到最小值373.9 mg·kg-1;8-9月份表土DOC含量迅速增加,9月份达到最大值443.7mg·kg-1.表土DOC特定波长吸收值也有明显的季节变化.随着时间的增长,280 nm波长吸收值(A280值)迅速增加,8～9月份达到最大值.A250/A365比值则明显的下降,9月份达到最小值,说明DOC结构也有明显的季节性动态变化.近期生物过程,如微生物代谢产物和消耗有机碳数量、植物光合产物(立枯物、根系分泌物)对DOC含量和组成结构季节动态有很重要的影响,而土壤中长期积累的有机质对其季节变化贡献很小.另外,温度和含水量通过影响的微生物活性间接影响DOC;降水的淋溶也对DOC动态有影响;冻融作用对春季DOC含量和组成结构有重要贡献.

The soil dissolved organic C （DOC） plays an important role in the cycling of wetland ecosystem. However, few studies have considered the seasonal dynamics of DOC and its impact factors in the marsh. The seasonal dynamics of DOC and its impact factors in the Doyeuxia augustifolia marsh soil was investigated. The results showed that the concentrations of DOC ranged from 373.9 to 443.7mg·kg^-1 , the mean was 414.61mg·kg^-1, and the variance coefficient was 7.7 % （ P 〈 0.0001 ） in the growing season. The variance of DOC concentration was significant in the growing season in the Doyeuxia augustifolia marsh soil. The concentration of DOC was higher in May. From June to July, the concentrations declined to the lowest value （373.9 mg·kg^-1） in July. The concentrations of DOC obviously increassed from August to September and reached to highest value （443.7 mg·kg^-1 ） in September. Meanwhile, the absorption values at 280 nm increased with time. In contrast, A250/A365 ratio decreased, showing the compositions of DOC also changed obviously in the growing season. Seasonal dynamics of DOC were controlled by the recent production of C, microbial lysis and metabolize, rather than by organic C that has accumulated in soil. Temperature and soil water content affected the DOC indirectly via microbial activity. Precipitation might induce leaching of DOC. The freeze-thawing also affected concentrations and compositions of DOC.