青土湖不同年限退耕地植被物种多样性及土壤酶活性研究

采用时空替代法，对甘肃省民勤县青土湖不同年限退耕地(退耕1 a、2 a、4 a、8 a、13 a、20 a、30 a、40 a)的植被演替特征、土壤酶活性进行调查，以耕地为对照(CK)，分析植被群落与土壤酶活性的相关性，以揭示其变化规律及其驱动机制，为青土湖区及其相似地区退耕地生态系统修复及生态环境建设提供理论基础。结果表明：(1)青土湖在退耕40 a自然恢复过程中，9个样方中共出现16科32属42种植物，物种构成表现为：多数种归于少数科，大部分植物种为单属单科。(2)随着退耕年限的增加，群落优势种由草本植物逐渐转化成灌木植物，植物种由退耕初期(1 a或2 a)的19种降低到退耕4 a的14种、退耕20 a的13种、退耕30 a的5种；退耕30 a时耐盐碱灌木植物盐爪爪成为该地的优势种，其重要值达到52.862，但退耕40 a时优势种盐爪爪的重要值降为36.008。(3)随着退耕年限增加，植物Margalef丰富度指数呈波动式下降的趋势；Shannon多样性指数和Pielou均匀度指数总体趋势呈先增加后减小，再逐渐趋于稳定；Simpson优势度指数整体变化幅度较小，最终呈稳定的趋势。(4)在不同土层(0~20 cm和20~40 cm)中，4种土壤酶活性随退耕年限增加总体表现出先升高后下降再逐渐趋于稳定的趋势，均在退耕8 a后显著下降，且磷酸酶和脲酶活性均显著低于蔗糖酶和过氧化氢酶活性；与对照样地(CK)相比，磷酸酶活性与脲酶活性均随退耕年限增加而下降；土壤磷酸酶、蔗糖酶和脲酶活性均随土层加深而降低。(5)相关分析结果显示，0~20 cm土层中，物种数与土壤蔗糖酶活性、磷酸酶活性以及脲酶活性均呈显著正相关关系；20~40 cm土层中，物种数与土壤脲酶活性呈极显著正相关关系，与土壤过氧化氢酶活性呈显著负相关关系；Margalef丰富度指数与0~20 cm土层的磷酸酶活性和蔗糖酶活性均呈显著正相关关系，与脲酶活性呈极显著正相关关系；20~40 cm土层中，Margalef丰富度指数与脲酶活性呈极显著正相关关系；Shannon多样性指数、Pielou均匀度指数和Simpson优势度与4种土壤酶活性间相关性较低且均不显著。研究认为，在青土湖区退耕地植被自然演替过程中，植物群落变得比较单一，物种多样性逐年降低，脲酶活性对物种多样性起着关键性作用。

Study on Vegetation Succession and Soil Enzyme Activities of Abandoned Land in Different Years in Qingtu Lake

Using space time substitution method, we investigated and analyzed the vegetation succession characteristics, changes in soil enzyme activities and their correlations for different years of abandoned land (returned fields 1 a, 2 a, 4 a, 8 a, 13 a, 20 a, 30 a, 40 a) in Minqin Qingtu Lake, farmland as control (CK), to explore the correlation between vegetation communities and soil enzyme activities, To reveal its change pattern and its driving mechanism, and to provide a scientific and theoretical basis for the restoration of receding farmland ecosystem and ecological environment construction in Qingtu Lake area and its similar areas. The results showed that: (1) Qingtu Lake during the natural recovery process after 40 a of fallowing, a total of 42 species, 32 genera and 16 families were found in 9 quadrats, the species composition is as follows: most species belong to a few families, and most species belong to a single genus and family. (2) With the increase of the period of returning farmland, plant species decreased from 19 species at the beginning of fallowing (1 a or 2 a) to 14 species at 4 a, 13 species at 20 a, and 5 species at 30 a. The saline tolerant shrub plant salt claw became the dominant species in this area at 30 a of fallowing, with a maximum importance value of 52.862.The importance value of the dominant species salt claw decreased to 36.008 at 40 a of fallowing. (3) With the increase of the period of returning farmland, there is a fluctuating downward trend in the plant Margalef richness index. The overall trend of Shannon diversity index and Pielou evenness index increased first, then decreased, and then gradually stabilized. Simpson dominance index has a small change range and a stable trend. (4) The activities of the four kinds of soil enzymes in different soil layers (0-20 cm and 20-40 cm) increased firstly, then decreased and then gradually stabilized with the increase of returning years. All decreased significantly after 8 a of farmland withdrawal, and phosphatase activity and urease activity were significantly lower than sucrase activity and peroxidase activity. Both phosphatase activity and urease activity decreased with increasing years of fallowing compared to the control sample plot (CK). Soil phosphatase, sucrase and urease activities all decreased with deepening of the soil layer. (5) Correlation analysis showed that, in the 0-20 cm soil layer, the number of species was significantly and positively correlated with soil sucrase activity, phosphatase activity and urease activity; in the 20-40 cm soil layer, the correlation between the number of species and soil urease activity was extremely significant and positive, while it was significantly negatively correlated with soil peroxidase activity. Margalef richness index was significantly and positively correlated with both phosphatase activity and sucrase activity in the 0-20 cm soil layer, and was highly significantly and positively correlated with urease activity; in the 20-40 cm soil layer, Margalef richness index was extremely significantly positively correlated with urease activity. The correlations between Shannon diversity index, Pielou evenness index and Simpson dominance with the four soil enzyme activities were low and none of them were significant. The research suggests that Qingtu Lake during the natural recovery process of 40 a of fallowing, the plant community became relatively simple, and the species diversity decreased year by year, urease activity played a key role in species diversity.