土地利用方式改变对湿地土壤总有机碳与可溶性有机碳的影响

为探明土地利用方式改变对湿地土壤总有机碳(TOC)和可溶性有机碳(DOC)含量的影响,采取空间替代时间的方法,测定了湿地、由湿地转变而成的林地、不同开垦年限的耕地和由耕地转变而成的果园土壤中TOC和DOC含量的变化。结果显示:湿地在开垦为耕地3 a后,土壤0~30 cm土层TOC含量显著(P<0.05)下降,开垦30 a后,只有0~10 cm的土壤表层TOC含量得到积累并恢复到与湿地相当的水平,表明湿地围垦后,土壤碳的丧失与积累在时间和空间上不对等,碳的损失发生期短,且集中在0~30 cm土层,碳的积累所需时间较长,且主要积累于0~10 cm土层。湿地、由湿地转变而成的新生耕地、林地DOC含量在土壤剖面上未表现出随土层增加而变化的趋势,DOC分配比例在除新生耕地外的4种土地利用类型中均表现为随土层增加而逐渐升高,说明DOC分配比例较DOC含量对土层深度变化更敏感,更适于表征DOC在土壤剖面方向上的变化。0~20 cm土层的DOC分配比例与土地利用方式无关。湿地在转变为耕地初期,20 cm以下土层的DOC分配比例下降,耕作30 a后显著(P<0.05)升高;耕地再转变为果园的3 a后,DOC分配比例在30~50 cm土层显著(P<0.05)降低;湿地在转变为林地后,各土层DOC分配比例未表现出显著差异。

Influence of land use changes on soil total organic carbon and dissolved organic carbon in wetland

In order to explore the effects of land use changes on soil total organic carbon (TOC) and dissolved organic carbon (DOC) in wetland, based on the concept of space as a substitute for time, the contents of TOC and DOC of wetland and four types of land changed from wetland, including two kinds of cultivated lands with different reclamation years, orchard land and woodland, were measured. The results showed that, three years after the wetland was reclaimed as cultivated land, TOC content in 0-30 cm soil layer decreased significantly (P<0.05), and thirty years after reclamation, only 0-10 cm topsoil TOC content was accumulated and restored to the same level as wetland. This indicated that the loss and accumulation of soil carbon were unequal in time and space after reclamation of wetland. The occurrence period of carbon loss was short and concentrated in 0-30 cm soil layer, and carbon accumulation took a long time and carbon was mainly accumulated in surface soils of 0-10 cm. The DOC content of wetland, newly cultivated land and woodland did not show an increasing trend with the increase of soil layer in soil profile, but the DOC/TOC increased with the increase of soil layer in four land use types except newly cultivated land. So, compared with DOC content, DOC/TOC was more sensitive to the change of soil depth, and was more suitable to characterize the change of DOC in the direction of soil profile. It was found that DOC/TOC in 0-20 cm soil layer was irrelevant to land use types, and at the initial stage of wetland conversion to cultivated land, DOC/TOC of soil layer below 20 cm decreased, but increased significantly (P<0.05) after 30 years of cultivation. After three years of conversion from cultivated land to orchard land, DOC/TOC decreased significantly (P<0.05) in 30-50 cm soil layer, while there was no significant difference in DOC/TOC among different soil layers after wetland was transformed into woodland.