半干旱沙地封育草场的植被变化及其与土壤因子间的关系

封育措施是一种主要的草场恢复和重建的措施。通过对半干旱沙地完全封育、季节封育和未封育地的比较分析,量化了不同封育措施下植被变化及其与土壤因子的关系。对3种封育措施群落组成和生物多样性的多响应置换过程(M RPP)分析结果表明,封育改变了群落的组成成分并增加了生物多样性,群落的指示种分析及样方相似性指数计算结果则显示,完全封育(>10a)的群落逐渐向旱生化发展,各植物种分布的空间异质性显著提高,放牧价值开始降低,而季节性封育则明显处于一种非平衡的稳定状态。对不同措施下植物种与土壤因子间关系除趋势对应分析(DCA)和除趋势典范对应分析(DCCA)排序结果表明,土壤水分状况是限制3种措施中植物种组成的决定性因子,生物结皮盖度、土壤有机质和土壤容重等因子均在一定的程度上对水分产生影响,其中最为突出的因子是生物结皮盖度,由于长期缺少牲畜的践踏,完全封育区内结皮发育较好,这也是导致群落向旱生化发展的原因之一,同时一些重要因子诸如降水的时空变化或由此而引发的土壤水分的时空变化在本研究中可能被忽略。相关分析表明3种措施的生物多样性除了受土壤水分状况(土壤含水量和结皮盖度)的影响外,还与土壤速效氮呈正相关,与速效磷呈负相关。

Vegetation variations under different exclusion measures and their correlation to soil factors

Exclusion has been applied as a main measure for revegetation all over the world.This paper,by comparing the results of year-round,seasonal and non-exclusion,quantified the vegetation variations under three different exclusion measures and their correlation to soil factors.The analysis results for community species component and plant diversity using MRPP showed that exclusion did change the species component and increase plant diversity remarkably,while the period of exclusion had no significant influence on these two community features.The indicator species analysis and calculation of similarity indices indicated that community for year-round exclusion is becoming xerophytization and unpalatability,and showed highly spatial heterogeneity of plant species distribution,whereas community for seasonal exclusion is under stable non-equilibrium condition.DCA and DCCA results of relationship between plant species and soil variables demonstrated that soil moisture is a controlling factor for plant species component,microbiotic soil crust cover,soil organic matter,and soil bulk density have significant effects on soil moisture,among which microbiotic soil crust is a leading fact due to its limitation to rainfall infiltration on one hand,and its constraints to entrance of herbaceous seeds into soil or to germination of soil seeds.As result of long-term removal of animal grazing,crust keeps intact in year-round exclusion community,which is one main reason of community xerophytization.It is also obvious from ordination results that some importantly environmental factors such as tempo-spatial change of rainfall and corresponding tempo-spatial change of soil moisture are neglected during direct gradient analysis. In addition,biodiversity has close relation to soil nutrients besides to soil moisture condition(soil water content and crust cover),biodiversity has positive relation to available N,and negative relation to available P.Higher soil N has advantage to non-leguminous plants growth on nutrition-poor sand land definitely.The impact of P to community component is unclear and should be studied from plant physiology.