【摘要】 土壤氮素(N)转化是生态系统重要的生态过程之一,可作为生态恢复评价的重要指标。以位于科尔沁沙地东南缘的章古台地区草地、30年生的樟子松(Pinussylvestrisvar.mongolica)、赤松(P.densiflora)和杨树(Populussimonii)人工林为对象,采用PVC顶盖埋管法和离子交换树脂袋法研究了土壤N矿化特征及其有效性。结果表明,生长季内土壤N净矿化量表现为草地(8.06μgg)和赤松林(9.06μgg)低于樟子松林(18.36μgg)和杨树林(17.88μgg)(p<0.05);树脂吸附的无机N表现为草地(283.50μggdryresin)和杨树林(297.00μggdryresin)最低,樟子松林(440.10μggdryresin)居中,而赤松林(835.65μggdryresin)最高(p<0.05)。综合分析林地土壤理化特性、矿化特征和N有效性,表明樟子松、赤松和小叶杨均可作为固沙造林选择树种,其表现为赤松>樟子松>小叶杨。认为深入开展生态系统N平衡研究有利于更好地评价固沙林的功能。更多还原

【Abstract】 The sand-fixation plantations played an important role in cutting down desertification process in northern China. Soil nitrogen mineralization, which is a key ecological process in poor sandy ecosystems, can be used as a basic index to assess ecosystem function of tree plantations. In this study, soil nitrogen mineralization process and its availability were examined by the methods of in situ closed-top PVC tube incubation and ion exchange resin bags under plantations of pine and poplar, and their neighboring grasslands in the southeastern Keerqin region of China. Results indicated that the accumulative net mineralization in growing season （from April 15 to October 15, 2004） in the grassland （8.06 μg·g -1） and Pinus densiflora （9.06 μg·g -1） plantation was lower than that in both Pinus sylvestris var. mongolica （18.36 μg·g -1） and Populus simonii （17.88 μg·g -1） plantations （p<0.05）. The ratios of nitrification rate to net mineralization rate in grassland, P. sylvestris var. mongolica, P. densiflora, and Populus simonii plantations were 0.88, 0.91, 0.82, 0.87, respectively, which indicated that the soil nitrification rate in the study area is more intensive than soil net ammonification processes, and the NO-₃-N was the major N form absorbed by plants in the study area, which might due to the higher soil pH values （>6.6） and strong human disturbances in the study area. The percentages of net mineralization amount to soil total N contents in grassland, P. sylvestris var. mongolica, P. densiflora, and Populus simonii plantations were 2.49%, 4.42%, 2.77%, 4.26%, respectively, implying that N turnover rates in grassland and P. densiflora plantation were very low, while those in P. sylvestris var. mongolica and Populus simonii were relatively higher. The accumulative mineral N absorbed by resin from May 15 to October 1 in both the grassland （283.50 μg·g -1 dry resin） and Populus simonii plantations （297.00 μg·g -1 dry resin） was the lowest, while that in P. sylvestris var. mongolica （440.10 μg·g -1 dry resin） was intermediate, and P. densiflora （835.65 μg·g -1 dry resin） was the highest （p<0.05）. Soil relative nitrification rate （which is expressed by the ratios of the soil NO-₃-N to mineral N） in the grassland, P. sylvestris var. mongolica, P. densiflora and Populus simonii plantations were 0.88, 0.87, 0.92, and 0.90, respectively, which also implied that soil NO-₃-N accounted for most of the soil mineral N. From this study, we conclude that the in situ closed-top PVC tube incubation method is more accurate than the ion exchange resin method in measuring seasonal soil N mineralization rate, while it is more convincing to use both methods in exploring both soil N availability and N absorption by plants. Based on the corresponding results, we concluded that the three tree species mentioned above were selective sand-fixation tree species in the study area, and the rank of suitability was P. densiflora, P. sylvestris var. mongolica and Populus simonii. However, to comprehensively assess the ecosystem functions in the study area, the knowledge of N balance in sand-fixation plantations is necessary.更多还原