黄土丘陵区主要植物根系对土壤有机质和团聚体的影响

植物根系是植物与土壤进行物质交换的通道,在土壤侵蚀严重、生态脆弱的黄土丘陵区,深入认识根系对土壤物理化学性质的影响具有重要意义。选取了白羊草(Bothriochloa ischaemum)、苔草(Carex lanceolata)、茭蒿(Artemisia leucophylla)、铁杆蒿(Artemisia sacrorum)、狼牙刺(Sophora viciifolia)、柠条(Caragana intermedia)6种植物作为研究对象,取0—10,10—20,20—30,30—40,40—50,50—60 cm土层根系和土样,分析不同土层各物种根长密度、根表面积密度、平均根直径、土壤有机质(SOM)、土壤容重以及各级水稳性团聚体重量百分含量。结果表明:所研究植物根系以细根为主。在0—20 cm土层中,白羊草、苔草根长密度显著大于其余植物(P0.05),表现为苔草白羊草铁杆蒿茭蒿狼牙刺柠条,平均根直径则相反。根系能不同程度地增加SOM含量,SOM含量与根系平均直径和根系表面积密度呈极显著的正相关关系(P0.01)。在土壤剖面上,水稳性团聚体重量百分含量明显减少的是白羊草、苔草和铁杆蒿样地,水稳性团聚体重量百分含量随土层深度变化不明显的是茭蒿、狼牙刺和柠条样地。根表面积、根长密度能够显著增加0.5～2 mm水稳性团聚体重量百分含量(P0.05),说明根系能够使小粒径团粒凝聚成更大粒径的土壤团粒。根系能够提高土壤有机质含量,增加中等粒径团聚体含量,改善土壤结构,提高土壤稳定性,对增加土壤抗蚀性起到重要作用。

Effects of Main Plant Roots on Soil Organic Matter and Aggregates in Loess Hilly Region

Plant root system is the channel of material exchange between vegetation and soil. In the loess hilly area with serious soil erosion and fragile ecology, it is great significance to deeply understand the influence of root system on soil physical and chemical properties. In this study, six plant species were taking as research objects, which were Bothriocheloa ischaemum, Carex lanceolata, Artemisia leucophylla, Artemisia gmelinii, Sophora viciifolia and Caragana intermedia. Roots and soil samples of 0-10, 10-20, 20-30, 30-40, 40-50 and 50-60 cm soil layers were taken. The root length density, root surface area density, mean root diameter, soil organic matter, soil bulk density and water stable aggregate content of each species in each soil layer were analyzed. The results showed that the roots of the species studied were mainly fine roots. In the 0-20 cm soil layer, the root length density of herbaceous plants was significantly higher than those of other species (P<0.05), which followed the order of B. ischaemum > C. lanceolata > A. leucophylla > A. gmelinii > S. viciifolia > C. intermedia, while the average root diameter was opposite. The root system could increase the SOM content in varying degrees, and the SOM content had a significant positive correlation with the root mean diameter and root surface area density(P<0.01). In the soil profile, the weight percentage of water-stable aggregate significantly decreased in the sample plots of B. ischaemum, C. lanceolata and A. sacrorum. The weight percentage of water-stable aggregates did not change significantly with depth in the sample plots of A. leucophylla, S. viciifolia and C. intermedia. Root surface area and root length density could significantly increase the weight percentage of water-stable agglomerates of 0.5~2 mm (P<0.05), which indicated that the root system could agglomerate small-size aggregates into larger-size soil aggregates. The above research results showed that root system could increase soil organic matter content and medium-size aggregate content, improve soil structure and soil stability, and played an important role in increasing soil corrosion resistance.