The Root Phenotypic Adaptation Of Populus Euphratica To The Floodplain In Extremely Arid Region

Populus euphratica is a dominant tree species of riparian forest in arid region of northwest China,the population play a key role for ecological balance of Oasis and development of local economy and society.Recently,its regeneration have been strongly impacted due to climate change and human activities.Standing along river is a main ecological habit for the tree,thus its ideal habitat for regeneration is floodplain,an ecotone between forest and inner rivers.However,the riparian soil environment in arid region often is heterogeneous and with various interferences.The root phenotypic plasticity of P.euphratica may play an important role for P.euphratica to generate successfully on the riparian soil environment.The goal of this study was to understand the root adaptation mechanism of field R euphratica to the riparian soil environment.We,on the one hand,investigated the root growth characteristics in field by digging the first-year seedlings grown in floodplain,and then quantified deep-rooting strategy of the first-year seedlings under drought stress through an experiment.On the other hand,we investigated the branching pattern of clonal roots of P.ehphratica in heterogeneous riparian habitat,and estimated the correlations between the clonal root traits and riparian soil factors to find the key factor driving changes of clonal roots.Our results suggest that(1)roots of first-year P.euphratica seedlings showed an obvious adaptation to arid riparian environment,the stocky stem,deep root,high root-shoot ratio and herringbone-like root architecture are adaptive features of the first-year seedlings to floodplain in arid region.(2)First-year P.euphratica seedlings depended on different levels of phenotypic adjustments to achieve deep rooting under drought stress.Under moderate drought they more relied on adjusting root architecture to increase relative root depth,but under severe drought they changed strongly in both root-shoot allocation and root architecture to increase root depth.The role of root morphological changes was always marginal.(3)The clonal roots of P.euphratica expressed different branching patterns in heterogeneous floodplain that can be concluded as two types:guerrilla-branching type(with sparser and longer branches,smaller branching angle in vertical and horizontal)or occupation-branching type(with denser and shorter branches,steeper branching angle in vertical and wider branching angle in horizontal).(4)The former more occurred on the edge of the river,and the later more occurred near the forest.Soil physical factor(soil texture and compactness)was the most important factor driving changes in branching patterm of the clonal roots.(5)The vertical branching angle of P.euphratica clonal roots showed a significant ecological plasticity in this study,it may also be an important adaptive trait for clonal woody plant and that should be paid attention in the future study about phenotypic plasticity of clonal plants.