平原造林工程影响下的河岸带土壤生态化学计量特征

北京主要河流河岸带实施平原造林工程后,对河岸带植被类型及土壤造成不同程度影响。研究河岸带原有及重建植被类型土壤生态化学计量特征,对河岸生态系统土壤碳氮磷平衡及固碳潜力提升提供科学依据。选取北京温榆河昌平段岸边原有植被类型3种样地(乔木林、乔灌林及草地),重建植被类型2种样地(乔木林与灌木林),共15个样方,采集3层(0—10,10—20,20—30 cm)土壤样品,分析并计算碳(C)、氮(N)和磷(P)含量及计量比。结果表明:原有与重建植被类型的土壤有机碳(SOC)、全氮(TN)、全磷(TP)含量分别为3.810~10.320,0.223~0.700,0.551~0.692 g/kg,C/N、N/P、C/P分别为11.592~25.373,0.373~1.022,5.662~15.493;SOC与TN均在表层聚集,且同N/P、C/P一样表现出随土层深度增加而减少趋势,C/N反之,TP受土层深度影响较小;原有植被类型(乔木林)土壤SOC和TN均高于其他植被类型,在10—20,20—30 cm土层间C/N、C/P均显著低于其他植被类型(P＜0.05);原有植被类型(草地)在0—10 cm土层间N/P最低;重建植被类型(乔木林)土壤TP含量显著低于其他植被类型;重建植被类型(灌木林) C/N显著高于其他植被类型。研究结果揭示了研究区土壤N素为植物生长的限制元素,乔木、乔灌林下土壤有机质释放更多,P有效性更高,固碳潜力强;重建植被类型有机质矿化较慢,固磷能力更强。因而,建议温榆河河岸带采用乔木纯林和乔灌混交模式来积累土壤有机质,提高河岸带生态系统土壤质量及固碳潜力。

Ecological Stoichiometric Characteristics of Riparian Soils Affected by Plain Afforestation Projects

After Beijing implemented plain afforestation projects in the riparian zones of major rivers, the vegetation types and soils in the riparian zones have been affected to varying degrees. The study of soil ecological stoichiometry characteristics of the original and reconstructed vegetation types in the riparian zone provides scientific basis for the soil carbon (C), nitrogen (N) and phosphorus (P) balance and the improvement of the C sequestration potential of the riparian ecosystem. Total 3 original vegetation types (arbor forest, arbor-shrub mixed forest and grassland) and 2 reconstructed vegetation types (arbor forest and shrub forest) were selected as experimental samples at 15 sites of Beijing Wenyu River Changping riparian zone. Soils were sampled at 3 layers (0-10, 10-20, 20-30 cm), and analyzed for the contents and measurement ratios of C, N and P. The results showed that the ranges of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) of the original and reconstructed vegetation types were 3.810~10.320, 0.223~0.700, 0.551~0.692 g/kg respectively, C/N, N/P, and C/P were 11.592~25.373, 0.373~1.022, 5.662~15.493 respectively. Both SOC and TN were concentrated in the surface layer, and like N/P and C/P, they decreased with the increases of soil depth, while the C/N was on the contrary. TP was less affected by the change of soil depth. The SOC and TN in the original vegetation types (arbor forest) were higher than the others. The C/N and C/P at 10-20 and 20-30 cm soil layers were significantly lower than the others (P< 0.05). The N/P of original vegetation types (grassland) was the lowest at 0-10 cm soil layer. The soil TP content of reconstructed vegetation type (arbor forest) was significantly lower than those of the other vegetation types. The C/N of reconstructed vegetation types (shrub forest)was significantly higher than the others. The study revealed that the soil N was the limiting factor for plant growth. Arbor and arbor-shrub mixed forest released more soil organic matter, had the higher levels of P availability, and had strong carbon sequestration potential. The re-vegetation types had the slower organic matter mineralization and stronger phosphorus fixation capacity. Thus, it''s recommended that the mixed mode of pure forest and arbor-shrub mixed could accumulate soil organic matter and improve the soil quality and carbon sequestration potential of riparian ecosystems in the Wenyu River riparian zone.