黄河三角洲盐碱地不同造林模式下的土壤碳氮分布特征

为了探讨不同造林模式对土壤碳氮影响的生态效应,以黄河三角洲盐碱地白蜡+棉花(FC)、香花槐+棉花(RC)、竹柳+棉花(SC)、白蜡林(F)、竹柳林(S)等5种造林模式为研究对象,分析比较各造林模式土壤的碳氮形态及分布特征,为重度退化刺槐林的经营改造和造林模式选择提供理论依据。结果显示:(1)不同造林模式下土壤的可溶性总碳和可溶性有机碳含量均高于裸地,农林间作高于纯林,其中SC模式含量最高,其次为FC和RC模式,而F和S纯林模式较低;5种造林模式不同土层可溶性有机碳含量均表现为0—20 cm高于20—40 cm。(2)农林间作模式0—40 cm土层的可溶性全氮和可溶性有机氮平均含量均高于纯林模式,其中SC模式的含量最高。FC、SC和S纯林模式0—20 cm土层可溶性有机氮含量显著高于20—40 cm土层,分别为其1.4、1.5和2.7倍;而RC模式20—40 cm土层可溶性有机氮含量显著高于0—20 cm土层。(3)5种造林模式中,除F纯林土壤硝态氮低于裸地外,其他造林模式下的土壤各种氮养分含量均显著高于裸地。土壤可溶性有机碳与全氮和铵态氮的相关性达到极显著水平(P0.01)。研究表明农林间作模式可显著提高重度退化刺槐林皆伐后土壤中有效态碳、氮含量,其中SC模式改良效果较好,而纯林模式较差。

Distribution characteristics of soil carbon and nitrogen under different afforestation modes of saline land in the Yellow River Delta

The Yellow River Delta is the largest estuarine wetland ecosystem in the warm temperate zone of in China and the most active land-ocean interacion regions among the large river deltas in the word. However, here rainfall was less and the mineral content in underground water was higher. These conditions caused soil salinization and alkalization. Soil affected by saline and alkaline constitute nearly 50 percent of total and surface. Therefore, the development of management strategies designed to reduce soil salinity has become a high priority in this region. However, a better understanding of ecological effects of different afforestation is necessary before targeted management strategies can be conceived. Thus, the objective of this study is to assess the effects of agro-forestry and pure forest on the organic carbon and nitrogen of saline soil in the Yellow River Delta. Total soluble carbon (TOC), dissolved organic carbon (DOC), total soluble nitrogen (TSN), soluble organic nitrogen (SON), NH₄⁺-N, NO₃-N and total nigrogen (TN) in soil taken from different afforest measures were analyzed. Five afforestation models were Fraxinus chinensis + Gossypium hirsutum (FC), Robinia pseudoacacia cv. Idaho + Gossypium hirsutum (RC), Salix babylonica + Gossypium hirsutum (SC), Fraxinus chinensis (F) and Salix babylonica (S). Compared with bare land, soil TOC and DOC contents in the combination of SC were highest among all treatments, followed by FC, RC,Soil DOC content in all systems tended to be higher in surface layer (0-20 cm) than in deeper layer (20-40 cm). Regardless of soil layers, the contents of TSN and SON were higher in agro-forestry than in pure forest,SC had the highest level of soil TSN and SON. The contents of SON in 0-20 cm soil layers were significantly higher than 20-40 cm soil layers under FC, SC and S, respectively was 1.4, 1.5 and 2.7 times of them. Conversely, the contents of soil SON in 20-40 cm were significantly higher than in 0-20 cm under RC. Among five afforestation measures, the contents of all kinds of soil nitrogen were significantly higher than bare land, excepted for the lower NO₃^--N contents under F. There was a positive correlation between the DOC,and TN and NH₄⁺-N (P<0.01). The conclusion indicates that the agro-forestry could significantly improve the contents of soil effective carbon and nitrogen, in particular, SC was the best afforestation model, while the pure forest was poor.