无定河流域植被恢复对土壤团聚体及碳固定的影响

Effects of vegetation restoration on soil aggregates and carbon sequestration in Wuding River catchment

对无定河流域坡耕地和4、5、10、30、50年植被恢复样地土壤水稳性团聚体含量,全土样及不同直径水稳性团聚体中的有机质、速效磷含量进行了测定分析,计算了土壤有机碳密度,旨在评价植被恢复对土壤结构、养分及土壤固定的影响。结果表明:各样地全土样有机质和速效磷含量分别介于6.73~31.83 g·kg-1和1.93~14.72 mg·kg-1之间,不同直径团聚体有机质和速效磷含量分别介于7.15~26.03 g·kg-1和3.71~16.64 mg·kg-1之间。相对农地,植被恢复能明显增加表层土壤有机质含量和有机碳密度,杜梨群落增加幅度最高,增加值分别为24.93 g·kg-1和91.98 mg·cm-2;水稳性团聚体以<0.05 mm和0.05~0.1 mm为主,含量分别在37.06%~57.22%和21.71%~29.76%之间;不同直径水稳性团聚体中有机质含量表现为>2 mm至0.2~0.5 mm之间,直径愈小,有机质含量愈高,0.2~0.5 mm至<0.05 mm之间,粒径愈小,有机质含量愈低;除1~2 mm团聚体中的速效磷含量最高外,>2 mm至<0.05 mm团聚体之间,粒径愈小,速效磷含量愈低。土壤有机碳密度与植被恢复年限呈线性正相关关系。相对于土壤碳固定,土壤抵抗水力侵蚀的能力需更长时间才能显著提高。相对慢速湿润,快速湿润条件下各直径水稳性团聚体有机质含量均较高。研究区大雨或暴雨是造成该区域土壤结构恶化和有机碳损耗的主要原因。

Content of soil water stable aggregates with different diameter,soil organic matter,and available phosphorus in whole soil samples and in aggregations of different diameter were measured in order to evaluate the effect of vegetation restoration on soil structure,nutrients and soil carbon sequestration. Soil samples were collected from slope cropland and vegetation restoration areas experiencing cropland abandonment 4,5,10,30,50 years in Wuding river catchment. The results showed that the content of soil organic matter and available phosphorus,was 6. 73 - 31. 83 g·kg^-1and 1. 93 - 14. 72 mg·kg^-1in whole soil samples,and 7. 15 - 26. 03 g·kg^-1and 3. 71 - 16. 64 mg·kg^-1in aggregations with different diameters. Top-soil organic matter and soil organic carbon density were increased significantly by vegetation restoration compared with cropping land,whose increases were most obvious at Pyrus betulaefolia community and increased by 24. 93 g·kg-1and 91. 98 mg·cm^-2. Soil water stable aggregates were mainly 〈0. 05 mm and 0.05 - 0. 1 mm,with the ratios being 37. 06% - 57. 22% and 21. 71% - 29. 76% respectively. The aggregate-associated organic matter content was the highest in 0. 2 - 0. 5 mm,which increased with decrease of diameter from 〉2 mm to 0. 2 -0. 5 mm but decreased with decrease of diameter from 0. 2 - 0. 5 mm to 〈0. 05 mm. The aggregate-associated available phosphorus content decreased with decrease of diameter from 〉2 mm to〈 0. 05 mm except 1 - 2 mm whose value was the highest. Linear positive correlation was observed between soil organic density and vegetation restoration years. Ittakes more years for the ability of soil water erosion resistance to be improved significantly compared to the improvement of soil carbon sequestration. The aggregate-associated organic matter content was the higher under fast wetting than slow wetting. Heavy rain or rainstorm may be the primary cause destroying soil structure and decomposing soil organic carbon at the area.