黄河源区高寒草原的植被退化与土壤退化特征

The characteristics of soil and vegetation of degenerated alpine steppe in the Yellow River Source Region

近几年,黄河源区高寒草原退化沙化明显。研究了黄河源区紫花针茅高寒草原在不同退化程度下植物群落、生物量和土壤的特征,结果表明,随着高寒草原退化程度加大,植被盖度、草地质量指数和优良牧草地上生物量比例逐渐下降,草地间的相似性指数减小,植物群落多样性指数和均匀度指数呈单峰式曲线变化规律。随着退化加剧,禾草地上生物量减少显著,杂草类植物地上生物量先增加后减少,而莎草科植物地上生物量的变化不受草地退化程度的影响。高寒草原土壤表层0～20cm的植物根系随土壤深度的增加而减少,随草地退化程度的加剧呈倒"V"型变化。高寒草原物种多样性与生物量之间呈"V"型变化规律,随着退化程度增加,物种丰富度与生产力的关系由显著正相关转变为负相关。随着高寒草原的退化程度加剧,土壤湿度、土壤有机质、速效磷、硝态氮、速效钾的含量和土壤紧实度都减小。随着高寒草原植被的退化演替,土壤退化越来越严重,贫瘠化不断加剧,到重度退化阶段,旱生沙生植物出现,呈现沙化初始景观。

In recent years,the alpine steppe in the Yellow River Source Region has shown obvious trends of degradation and desertification.We studied the different plant communities,biomass and soil characteristics of the Stipa purpurea alpine steppe at different degradation stages.With an increase of alpine steppe degradation,the vegetation coverage,grassland quality index and the proportion of excellent aboveground biomass forage gradually declined and the grassland similarity index decreased.As degradation increased,the plant diversity index and evenness index trend were both single-peak type curves.With increased degradation,grass aboveground biomass was significantly reduced and that of forbs was significantly increased at the beginning,but it was reduced during the mid-late period.The sedge above-ground biomass was not influenced by grassland degradation.The below-ground biomass of alpine steppe plant roots in the 0-20 cm soil profile was increasingly reduced as soil depth increased while the root biomass changed into an inverted ＂V＂ type.The ＂V＂ shape,with increased degradation,the relationship between species richness and productivity converted significant positive correlation of soil organic matter,available phosphorus,nitrate nitrogen,available potassium and soil compactness concentrations were reduced.With the succession of alpine grassland degradation,soil degradation became more serious.In the severe degradation stage,desert plants appeared,and the landscape developed a desert appearance.