黄土高原森林边缘区退耕地植被自然恢复及其对土壤养分变化的影响

Spontaneous succession and its impact on soil nutrient on abandoned farmland in the northern edge of the forest zone on the Loess Plateau

对黄土高原森林边缘区退耕地植被自然恢复及其对土壤养分变化影响的研究结果表明,该区植被演替虽然总体上具有典型森林区植被演替的特征,但多年生禾草阶段与多年生蒿类演替并没有表现出严格的先后顺序;群落物种多样性、丰富度、均匀度及物种替代率随植被恢复表现出由低而高,而后又降低的变化趋势。其变化的峰值阶段与多年生禾草阶段和多年生蒿类交错出现的阶段相吻合。土壤养分变化表明,该阶段也是退耕地养分消耗与累积处于平衡的阶段,具有明显的过渡性。不同养分对植被恢复的响应程度从高到低表现为:有效氮>有机质>全氮>速效钾>速效磷>全磷,而且在植被恢复过程中土壤养分累积具有明显的表聚性,尤以有机质、全氮、有效氮和速效钾表现明显。各养分的相关性分析表明,土壤有机质、全氮、有效氮与速效钾相互间显著相关,而全磷和速效磷与其余各养分间的相关性较小,而且磷素养分在植被恢复过程中的变化较小。对植被演替进行人工调控,应充分认识养分变化的这种差异。

Soil is crucial to vegetation restoration. Understanding the process of community succession and its impact on soil nutrients will provide important implications for the acceleration of community succession by human intervention. On the Loess Plateau, vegetation restoration is the focus of environment improvement yet little work has been done on the restoration of natural vegetation and how to accelerate this process. In study, the changes in vegetation community and their impact on soil nutrients in abandoned farmlands on northern edge of the forest zone on the Loess Plateau were studied. In general, the community succession of a community succession in the forest zone. However, the artemisia and gramineal grasses were different this the was and did not follow the order of a typical succession. The species diversity, abundance and evenness increased from the early stage of succession and reached the highest values after about 20 years, then decreased to a relatively constant level. The rate of species replacement changed in the same way. Soil analysis of nutrient changes indicated that the period with high rate of species replacement coincided with the period when soil nutrient depletion was in equilibrium with soil nutrient accumulation, indicating transitional characteristics in this period. This may have implications for human intervention in accelerating community succession. The study also demonstrated that soil nutrients responded to the process of community succession in the following order： available nitrogen〉 soil organic matter〉 total nitrogen〉available potassium〉 available phosphorus〉 total phosphorus. During the restoration, nutrients, especially the soil organic matter, total nitrogen and available nitrogen and po- tassium, concentrated in the surface layer. This may be explained by the high correlations among these four kinds of nutrients. Although total phosphorus and available phosphorus also showed a high correlation with each other, they showed low relativity with the other four kinds of nutrients, and changed little during the res- toration process, especially the total phosphorus. These differences must be taken into account when attempting to accelerate natural succession by human intervention.