土地利用对石漠化地区土壤团聚体有机碳分布及保护的影响

对贵州省关岭县石漠化地区不同土地利用方式下的土壤团聚体的稳定性、有机碳分布以及大团聚体有机碳矿化进行了研究,探讨了大团聚体对有机碳的保护作用,以期为选择合理的石漠化治理措施提供科学依据。选取了当地主要的4种土地利用方式,分别为水田(水旱轮作)、旱地、花椒林和火龙果林;其中花椒林和火龙果林位于石漠化治理区内。采用湿筛法分离出各级土壤团聚体并结合室内恒温培养法测定原状和破碎大团聚体中有机碳的矿化动态变化,其中大团聚体保护性碳含量为破碎与原状大团聚体有机碳在42 d内累积矿化量的差值。结果表明:土地利用方式对土壤团聚体稳定性具有显著影响。水田土壤团聚体稳定性要明显优于旱地、花椒林和火龙果林,且后3种土地利用方式间也存在显著差异。土壤有机碳也受到土地利用方式的影响,水田和旱地土壤有机碳含量要明显高于火龙果林和花椒林。各粒级团聚体有机碳含量在土地利用方式间具有较大差异,2 5 mm、0.25 2 mm和<0.25 mm团聚体中有机碳含量按水田、火龙果林、旱地和花椒林依次下降,5 8 mm团聚体中有机碳含量则以花椒林最高,其次是水田和火龙果林,旱地最低。但是就各粒径团聚体的有机碳库而言,<0.25 mm团聚体是土壤有机碳的主要载体。花椒林、旱地、火龙果和水田的大团聚体保护性碳含量分别为83.37、78.86、73.81,61.04 mg/kg,其差异表明花椒林土壤大团聚体对有机碳的保护作用最强,其次是旱地和火龙果林,水田最弱。因此,在该地区种植花椒林和火龙果林可以改善其土壤质量,其可能机理是通过增加土壤中大团聚体含量,同时增强大团聚体对有机碳的保护作用。

Effects of land use on distribution and protection of organic carbon in soil aggregates in karst rocky desertification area

Under the global climate change, land use patterns, as one of the most important indicators that influencing the mineralization of soil organic carbon and the distribution of soil organic carbon in soil aggregates, have been increasingly focused on. However, accumulated publications presently showed that very few studies have paid a lot of attention to mineralization carbon, aggregate protected carbon, distribution of soil organic carbon in aggregates and soil aggregate stability effecting on them in karst rocky desertification area. In this paper, stability of soil aggregates, distribution of soil organic carbon and mineralization of organic carbon in macroaggregates under different land use patterns were studied. At the same time, the protection function of macroaggregates to organic carbon was discussed. The objective was to have scientific means for choosing appropriate measures to rehabilitate rocky desertification land. A research trial with four main land use patterns was sampled in karst rocky desertification area, Guanling County, Guizhou province. Soil aggregates were separated by wet sieving. Mineralization of organic carbon in intact and crush macroaggregates was tested by incubation in laboratory. Aggregates protected carbon was measured using methods of wet sieving after 42-day incubations of intact and crush macroaggregates of size <0.25 mm. The results showed: stability of soil aggregates and distribution of organic carbon in each size aggregate was obviously influenced by land use patterns. The mean weighted diameter of aggregates (MWD) was the rank with paddy soil>cropland>Chinese prickly ash orchard>Pitaya orchard. Stability of soil aggregates in paddy was greater than that in dryland, Chinese prickly ash orchard and Pitaya orchard. The content of organic carbon in paddy and dryland was higher than that in Chinese prickly ash orchard and Pitaya orchard. The distribution of organic carbon in each size aggregate was pronounced difference between land use patterns. Organic carbon content of 2 5 mm, 0.25 2 mm and <0.25 mm aggregate was decreased associated with the rank of paddy, Pitaya orchard, dryland, and Chinese prickly ash orchard. But, organic carbon content of 5 8 mm aggregate was highest in Chinese prickly ash orchard and lowest in dryland. The content of macroaggregates protected carbon under Chinese prickly ash orchard, dryland, Pitaya orchard and paddy was 83.37 mg/kg, 78.86 mg/kg, 73.81 mg/kgand 61.04 mg/kg, respectively. The difference above-mentioned of macroaggregate protected carbon content suggested that the protection of macroaggregate to organic carbon was strongest in Chinese prickly ash orchard, followed by dryland and Pitaya orchard and weakest in paddy. That is, Chinese prickly ash orchard can improve the content of soil macroaggregate. Certainly, macroaggregate protected carbon concentration also was increased in Chinese prickly ash orchard than that in other land use patterns. Therefore, planting Chinese prickly ash and Pitaya can improve soil quality, due to increasing macroaggregate concentration and enhancing protection of macroaggregate to organic carbon. The policy implications of this study was that soil in karst rocky desertification area can been managed through changing land use patterns to accumulate more soil organic carbon, in order to reduce the emission of carbon from soil to atmosphere.