Effects Of Drought And Rewatering On The Growth And Physiological Characteristics Of Kentucky Bluegrass

Kentucky bluegrass(Poa pratensis)is a main planting material for cold-season lawns around the world.However,the resources of bluegrass for planting in China were completely depended on imports,while the plants often characterize by poor drought resistance.Therefore,breeding wild turfgrass varieties with strong drought resistance from wild germplasm resources is one of the effective ways to plant turfgrass in water-deficient regions in northern China.Based on the studies of our team,six accessories of materials in Shanxi and 33 commercial varieties materials were selected,and classified by the evaluation of drought resistance.The experiment was conducted in smart greenhouse using random block design.After two months in the nursery of the materials in smart greenhouse,the drought treatments would be treated as the gradients of 100% evapotranspiration(ET),80% ET,60% ET and 40% ET,respectively.The watering was stoped after the treatment of 40% ET and carried out drought treatments for one,three,and six weeks,respectively.A biological repeat was sampled from each variety,and was rehydrated with 80% ET for two weeks.The relevant indicators of drought resistance were measured after each stage.The main test results were as follows:At the initial stage of different water treatments,the chlorophyll content of 11 test materials showed significant differences compared with the controls,while the maximal decrease was presented on Midnight(26.5%).The aboveground biomass of the materials at 60% ET stage was significantly lower than that in the 80% ET stage.At this stage,the chlorophyll content of 18 test materials showed significant differences compared with the control,while the contents of 12 test materials(included Bandera,Beyond,Fielder,Good spring,Jackpot,LQ,Midnight,NW,YX,Best Blue,Blue Devil and Diva)were significantly lower than control treatment.The leaves fresh weights of 23 test materials were significantly lower compared with the control treatment in the 40%ET stage.For NDVI,all of the test materials were significantly decreased compared with the control treatment,except the Bluemoon,while the decreasing margins of 14 test materials’ NDVI exceeded 10%.For the leaves relative water content,there were 26 test materials indicated significant reductions in drought treatments compared with the control treatment,while the maximal reduction was 68.57%(presented in HY).Compared with the control treatment,the leaves fresh weight of 26 test materials and the leaves relative water content of 33 test materials were significantly improved after rewatering,while the maximal increase reached 50%(GinneyⅡ).However,all of test materials showed poor recovery in chlorophyll content and NDVI.The aboveground biomass of the most of test materials in drought treatments was lower than the control treatment.The chlorophyll contents of 30 test materials’ in drought treatments were decreased more than 50% compared with the control treatment after three weeks of drought stress.The differences of root volume of the test materials in 0-10 cm soil layer were realtviely small between drought and control treatments,however,the corresponding differences of 10 test materials were significantly higher in the 10-20 cm soil layer in control treatment.When the drought stress reached six weeks,the above-ground parts of 25 materials stopped growth completely,while their NDVI and chlorophyll contents were significantly lower than control treatment.In this stage,meanwhile,12 test materials showed significantly higher root volume than the control treatment in the 0-10 cm soil layer.However,in the 10-20 cm soil layer,only Everesr presented significantly higher except root volume in drought treatments than control.The clustering analysis were carried out with the drought-tolerant indexes after six weeks of drought stress and two weeks of rewatering.The results showed that 39 test materials could be divided into 4categories with the threshold as 5.86.The category Ⅰ included Action,Impcat,Navy,Midnight,Beyond,Luck star,Camas,Geronimo,Comet,Diva,Fielder,Bandera,GinneyⅡ,Bluechip,Blue moon,My Holiday Lawn,Heidi,Blue Ghost,Jackpot,Martha and Nuglade,which showed the best drought resistance among the test materials.The category Ⅱ included Arcadia,Jackrabbit,Park,Wellington,Pure Blue,Blue devil,Everest,HY and Good spring belonged to category Ⅱ,which exhibited relatively good drought resistance among the test materials.The category III included Best Blue,Rhythm,LQ,Kentucky,WT and YX,which showed the general drought resistance among the test materials.The category IV included Meirt,QS,and NW,which presented the worst drought resistance among the test materials.According to the results of the cluster analysis and the performances of wild populations under drought stress,HY could be classified as Common;LQ,WT,and YX could be classified as Aggressive;QS and NW could be classified as BVMG.In summary,2/3 of the test materials showed the compensated effects after a short period of drought and rewatering with degrees.However,the effects of compensation were also gradually reduced by prolonging drought.The genotyping of wild populations of the current study could further standardizes the selection of wild native grass species,and has great significance for the breeding of native varieties in Shanxi.