华北低丘山地不同土地利用方式下土壤团聚体及其有机碳分布特征

土地利用变化影响土壤团聚性及有机碳分布，进而改变土壤碳循环过程。对太行山南部50年刺槐人工林（R50）、17年刺槐人工林（R17）、自然恢复林（NR）和农田（CL）等不同土地利用方式下的表层土壤（0-20 cm）进行了系统研究，利用湿筛法对土壤团聚体进行分级，并计算土壤结构稳定性参数（平均重量直径MWD，团聚体比例AR）及不同粒径团聚体有机碳贡献率，进而分析弃耕后土壤团聚体分布及团聚体有机碳含量变化。结果表明，土地利用方式对土壤团聚体粒径分布及团聚体有机碳含量有显著影响，自然恢复林与刺槐林的大团聚体（>0.25 mm）含量都高于农田，且自然恢复林的大团聚体增加更显著。MWD的计算结果表明：自然恢复林 > 刺槐人工林 > 农田，说明该区域的自然恢复方式更容易促进大团聚体的形成，并显著改良土壤结构及增强土壤团聚体稳定性。弃耕后，不同土地利用方式0-10 cm土层各粒径团聚体有机碳含量均高于农田，且团聚体有机碳含量与团聚体稳定性呈正相关。这些结果说明，研究区域的自然植被恢复和人工造林都可以显著提高土壤的固碳能力，且储存的有机碳主要存于大团聚体中，而农田的有机碳大都存于粘粒+粉粒团聚体中。自然植被恢复和人工造林均提高了土壤结构稳定性，是改善团粒结构、提高土壤质量的有效方式。

Soil aggregate and its organic carbon distribution characteristics at different land use patterns in hilly areas of north China

Land use patterns affect the organic carbon distribution of soil aggregates and the carbon cycle process. In this study, a 50 years-old (R50) and a 17 years-old (R17) Robinia pseudoacacia plantations, a natural restoration forest (NR), and a cropland (CL) in the south Taihang hilly area were studied. Soil aggregates size distribution was determined by the wet-sieving method, and the organic carbon contribution and stability indexes of soil aggregates were calculated. The results showed that land use patterns had significant impact on the particle size distribution and organic carbon content of soil aggregates. The content of large aggregate (>0.25 mm) in the natural restoration forest and Robinia pseudoacacia plantations was larger than that in the cropland. The increasing of large aggregate (> 0.25 mm) content in the natural restoration forest was more significant. The calculated mean weight diameter (MWD) was in the order of NR>Robinia pseudoacacia plantations>CL. It indicates that the natural restoration forest in the studied region is easier to form large aggregates than other land uses due to few manual disturbances. In 0-10 cm layer, the organic carbon content of soil aggregates with different diameters at three forests was larger than that of cropland. Moreover, the organic carbon content of various aggregates was positively related with the stability of aggregates. These results shows that the conversion of cropland to plantations is capable of improving soil carbon sequestration capacity in the studied region, and the organic carbon is stored mainly in the large soil aggregates. In the cropland, however, most of the organic carbon is stored in the silt and clay of soil. The natural restoration forest and Robinia pseudoacacia plantations both are the effective land use patterns for improving soil structure and soil quality.