鄂尔多斯高原草地灌丛化不同阶段主要植物水分利用特征

Water use characteristics of main species in different shrub encroachment stages on Ordos Plateau

草地灌丛化是全球草地退化的普遍现象,理解草地灌丛化的过程和机制对灌丛化草地的恢复十分必要。目前有多种假说解释草地灌丛化现象,尽管大部分假说认为灌木和草本植物对土壤水分的不同利用方式在草地灌丛化过程中发挥着重要作用,但有关直接实验证据仍十分缺少。本文通过对鄂尔多斯高原流动沙地沙米群落、半固定沙地油蒿群落、固定沙地油蒿群落和固定沙地本氏针茅群落4个演替阶段植物群落的调查,采用稳定同位素分析的方法,分析不同阶段主要物种对不同水源的利用比例。结果表明:在不同演替阶段,草本植物对土壤水分的利用主要集中在土壤表层(0～20 cm),而灌木植物对中深层(50～200 cm)土壤水分的利用较多;灌木植物水分利用的可塑性强,在遭受水分胁迫时,灌木植物能够根据土壤水分的可利用性而改变对不同土层水分的利用。以上结果对于认识鄂尔多斯高原不同演替阶段主要植物水分利用策略具有一定意义,同时表明降低放牧等人为因素对表层土壤的干扰,改善表层土壤结构,提高表层土壤含水量是鄂尔多斯高原油蒿灌丛化草地恢复为地带性本氏针茅草原的关键。

Shrub encroachment occurs in degraded grasslands worldwide. Most hypotheses about shrub encroachment suggest that the differences of water use strategies between shrubs and herbaceous species are important,but with limited empirical evidence. Based on filed survey of four different succession stages( Agriophyllum squarrosum community in shifting sandy land,Artemisia ordosica community in semi-fixed sandy land,A. ordosica community in fixed sandy land,and Stipa bungeana community in fixed sandy land) on the Ordos Plateau,we examined the changes of water use characters of dominant species in different succession stages by determining water source through δ18O analysis. In different succession stages,herbaceous plants mainly used water from shallow soil layer( 0-20 cm),whereas shrubs predominantly used water from middle or deep soil layers( 50-200 cm). The plasticity of water use by shrubs was stronger than that of herbaceous plants. When suffering water stress,shrubs can change their water use sources to different soil layers according to water availability. These findings improve our understanding of water use strategy of the main species at different successional stages on the Ordos Plateau. The results suggest that it is crucial to reduce human disturbances such as overgrazing,to improve soil structure and increase soil moisture in shallow soil,and consequently to restore zonal S. bungeana steppe from A. ordosica encroached grassland on the Ordos Plateau.