Studies On Growth And Physiological Adaptation Strategies Of Agropyron Mongolicum Under Drought Stress

Agropyron mongolicum Keng.,a perennial grass with characteristics of drought resistance,cold resistance,salinity tolerance,and sand resistance,is widely distributed in desert steppe.It is the preferred species for restoration of degraded grassland,and it is also an important forage resource and a valuable gene pool for crop improvement.In this study,the seeds of A.mongolicum from four natural populations(represented by D,Q,H and G)in desert steppe from Dashuikeng Town,Qingshan Township,Huamachi Town and Gaoshawo Town in Yanchi County,Ningxia were used as materials.The pot control experiments were conducted to set normal water supply(75-80%FC,CK),moderate stress(50-55%FC,MS)and severe stress(30-35%FC,SS)by using the field water holding capacity as the standard.The phenotypic plasticity,component resource allocation and physiological characteristics of roots and leaves of A.mongolicum were studied to explore the response of phenotypic and physiological characteristics of A.mongolicum from different populations to drought stress.The main results are as follows:(1)The phenotypic characteristics of A.mongolicum from different populations showed that leaf length,leaf width,leaf thickness,leaf surface area and specific leaf area decreased with the aggravation of drought stress,while leaf tissue density,leaf dry matter content,specific root length and specific root area increased.Root length,root surface area,root volume,root bifurcation number,root tip number and root tissue density were the highest under moderate drought stress.Under moderate drought stress,the leaf surface area and leaf dry matter content of A.mongolicum from population D were lower,and the root specific surface area and specific root length were higher.Under severe drought stress,the root length,root surface area and root volume of A.mongolicum from.D population were lower.(2)Drought stress inhibited the growth of A.mongolicum individuals from different populations,and its plant height,total biomass,aboveground biomass and leaf biomass decreased significantly with the intensification of drought stress(P<0.05).The underground biomass and stem biomass(except for D population source)increased first and then decreased with the increase of drought stress,which were 0.33-0.34 g and 0.47-0.50 g under moderate drought stress,respectively.At each water gradient,the total individual biomass and the biomass of each component of A.mongolicum were lower from the D population.(3)The chlorophyll a contents of A.mongolicum from D and G populations increased gradually with the intensification of drought stress,while the total chlorophyll,chlorophyll-b and carotenoid contents increased first and then decreased with the intensification of drought stress.The drought stress significantly increased the activities of antioxidant enzymes and the contents of soluble sugar,proline and malondialdehyde(P<0.05).Under moderate drought stress,the contents of free amino acids,soluble protein,superoxide anion and its production rate of A.mongolicum from D population were higher than those of control and severe drought stress.The superoxide anion content and production rate of A.mongolicum from Q and H populations increased with the intensification of drought stress,while the superoxide anion content and production rate of A.mongolicum from G population were the lowest under moderate drought stress.(4)The changes of root surface area,root specific surface area and specific root area of A.mongolicum from different populations enhanced the resistance to drought stress and improved the environmental adaptability.In addition,compared with moderate drought stress,A.mongolicum from D population also improved stress resistance by increasing root-shoot ratio and decreasing root bifurcation number and root tip number.The A.mongolicum from the Q population adapted to water changes by reducing root length.The A.mongolicum from H population source increased its viability by reducing root tissue density,Chlorophyll.The A.mongolicum from G population adapted to drought stress by reducing root length and increasing proline and catalase activity.In summary,the A.mongolicum from different populations can adapt to drought stress to a certain by reducing specific leaf area,increasing leaf dry matter content,specific root length,specific root area,increasing the input of root resources and other phenotypic plasticity changes,and regulating the activation of antioxidant system and internal metabolic.However,with the aggravation of drought stress and the prolongation of time,the growth of A.mongolicum will be damaged and even die.