The Effect Of Drought Stress On Root Respiration And Yield In Three Spring Wheats

In the interest of understanding the relation beween carbon consumption in root system and yield formation in the wheat,three wheats of plant were selected: 'heshangtou'(H,a native cultivars widely planted during 50s and 60s of latest century),'gaoyuan602'(G,cultivated at late 70s in Qinghai and introduced in Gansu at 80s)and 'longchun8275'(L,the neoteric cultivars cultivated in 1996).A potted plant experiment was conducted under the rain-shelter to investigate effects of water lack on root respiration and yield in three spring wheats.Two water treatments were employed including well-water supply(W,75%～80%of field water capacity)and drought stress(S,45%～50%of field water capacity).In order to analyze and study the effect of drought stress to root respiration and yield,we took the measurations of photosynthesis rate,shoot biomass,root biomass,plant height,tiller,leaf area,root respiration,rhizosphere microbial respiration and gain yield in jointing stage, flowering stage,and mature stage.For every pot,the root respiration and rhizosphere microbial respiration showed the "low—high—low" tendency during the whole growth period,and the average value of antiquity native cultivar H is the highest,the root respiration and rhizosphere microbial respiration were 1.485and 0.0537 mgCO₂plant^-1h^-1respectively.The minimum of these two traits occurred in neoteric cultivar L;they were 0.912 and 0.0452 mgCO₂plant^-1h^-1respectively.But specific root respiration(the root respiration of unit biomass)and specific root rhizosphere microbial respiration(root rhizosphere microbial respiration of unit biomass)were higher in cultivar G;they were 6.44mgCO₂g^-1h^-1and 0.473 mgCO₂g^-1h^-1respectively. The root to shoot ratio of three cultivars in S were higher than in W.For both G and L, the root to shoot ratio were lower than H significantly.The R/S of H,G and L were reduced 19.6%,14.6%and 6.01%respectively by drought stress.Daily root respiration carbon and daily exudation carbon(RE)were the main part of total carbon consumption(C_T),and results showed the percentage of RE to C_T exceed 50,even exceed 100 during the mature stage,and RE of G and L were lower than H significantly.For G and L,the ratio of daily photosynthetic rate of entire plant(P_T)to C_T(P_T/C_T)were higher than H significantly;the P_T/C_T of H,C,L were 3.59,5.29 and 5.55 respectively.The root efficiency in drought stress was lower than in well-water supply significantly.Root efficiencies of G and L were 0.067g/mg and 0.061g/mg respectively which were higher than that of H.Drought stress enhanced the water use efficiency(WUE).The WUE of medium-term cultivar G and neoteric cultivar L both higher than native cultivar L in the two water treatments.The higher gain yield and higher assimilative matter use efficiency of L is the main factor in variety subrogation.