选取不同年限退/弃耕地（退耕1 a、2 a、4 a、8 a、13 a、20 a、30 a、40 a和CK）为研究对象,采用时空替代法,分析了不同年限退/弃耕地植被群落特征和土壤理化性质及其相关性。结果表明：（1） 石羊河下游青土湖退/弃耕地40 a的植被恢复过程中,9个样方共出现15科29属43种植物,退/弃耕地物种构成表现为：多数种属于少数科、少数种属于多数科。植被演变分为：一年生草本和多年生植物快速生长期（1~2 a）,一年生草本向多年生草本演变期（2~8 a）,多年生草本向灌木演变期（8~20 a）和以灌木为主的稳定期（20~40 a）;（2） 随退耕年限增加,土壤含水量呈先减小后增加最后波动式减小趋势,上层土壤含水量高于下层土壤含水量。各样方比例最大是细砂粒,粉粒次之,比例最小的是粗砂粒和黏粒,随退耕年限的变化,各粒径占比变化不大;（3） 随退耕年限增加,土壤全氮和有机质均呈下降趋势,速效钾含量呈先增加后减小趋势,速效磷含量呈先减小后增加再减小趋势,表聚现象明显;（4） 植被群落演替与土壤理化性质具有密切相关性。Margalef丰富度指数与土壤全氮和有机质呈极显著正相关关系,Shannon多样性指数与土壤容重和细砂粒呈显著的正相关关系,与土壤黏粒和粉粒呈显著负相关关系。退耕第4 a是青土湖退/弃耕地在恢复治理过程中关键时期。

We selected arable areas with different years of abandonment (1 a, 2 a, 4 a, 8 a, 13 a, 20 a, 30 a, 40 a, and CK) as research objects and used the space-time substitution method to analyze the vegetation community and soil physical-chemical characteristics during the restoration period at the Qingtu Lake. Our results showed that 15 plant families, with 29 genera and 43 species appeared in our plots during the 40-year restoration process, with most species belonging to a few plant families and few species belonging to one dominant plant family. We divided the vegetation restoration process into four stages. The first rapid-recovery stage (grain for 1a to 2 a) is composed of annual and perennial root herbs; the second stage (grain for 2 a to 8 a) is composed of annual herbaceous and perennial herbaceous plants; in the third stage (grain for 8 a to 20 a), perennial herbaceous and perennial shrub are the most common species; and perennial shrubs dominate the fourth final succession stage (grain for 20 a to 40 a). In areas where farming activities were more intensive, the soil-water content was more volatile, with increasing and decreasing periods. In the final succession stage, the topsoil layer had more moisture in compasrison to the lower-soil layer. Independent of the restoration stage, the proportion of fine sand grains was the largest, followed by the proportion of powder grains, whereas the proportion of coarse sand grains and clay grains were the smallest, and these particle proportions did not change depending on time and intensity of farming activities. We observed that according to the intensity of the farming activities, both total nitrogen and organic matter showed a downward trend. Still, the soil’s available potassium first increased and then decreased, whereas the available phosphorus showed the opposite trend. The surface aggregation phenomenon was evident. Finally, the succession of the vegetation community was closely related to soil physical-chemical properties. The Margalef richness index positively correlated with total soil nitrogen and organic matter, whereas the Shannon diversity index positively correlated with soil bulk density and fine sand particles and negatively correlated with soil clay and silt particles. The 4th year of the return of farming activity was crucial in the recovery process at Qingtu Lake.