The Effects Of Inter-Plant Competition On Yield Formation Of Spring Wheat Cultivars

This study was concerned to determine the effect of both inter-cultivar and intra-cultivarcompetition on the growth of three spring wheat (Triticum aestivum L.) cultivars atpopulation level and individual level respectively.The three cultivars released in differentperiods ("old"cultivar Heshangtou,HST;"recent"cultivar Gaoyuan602,GY602;and"modern"cultivar Longchun 8275,LC8275) that had different root:shoot ratios,differed inwater extraction from dry soil and plant height.In field experiment,two water regimes(irrigated treatment,IR;rainfed treatment,RF) were imposed to compare competitive effects;in pot experiment,the competitive ability of three spring wheat cultivars were investigated byimposing progressive drying of three soil water available gradient (sufficient water supply,SW;medium drought,MD and severe drought,SD).The results of field experiment were:1.Grain yield in monoculture were 8530 and 5620 kg ha^-1 for LC8275,8060 and 5850 kgha^-1 for GY602,5860 and 4480 kg ha^-1 for HST in IR and RF treatments.The WUE_Gwere 2.16 and 1.68 kg m³ for LC8275,2.20 and 1.63 kg m³ for GY602,1.40 and 1.18 kgm³ for HST.New cultivars had significantly more grain yield and higher water useefficiency for grain (WUE_G) than the old cultivar (P＜0.05).Under the two water regimesthe old cultivar had more root biomass,which contained to 459.2 and 399.9 g m^-2,whilein GY602 were 407.6 and 339.8g m^-2,and LC8275 were 318.0 and 257.3 g m^-2.The rootsize was biggest in HST and was significantly differed among the three cultivars (P＜0.05).Due to the different ability of water uptake,HST extracted water in deeper soillayers,whereas the modern cultivars extracted more water in upper and dry soil layers.2.The old cultivar benefited from inter-cultivar competition,which showed high grain yieldin mixtures than in monoculture,while GY602 and LC8275 showed significantly reducedgrain yield in mixtures compared to in monoculture;for HST the relative biomass yieldalways beyond 1,whereas for GY602 and LC8275 were always below 1,whichsuggested that HST benefited from competition and at the expense of the other twocultivars,the recent and modern cultivars decreased plant size in mixtures significantlyafter DAS70 compared to plants in monoculture. 3.Our study showed that the sequence of competitive hierarchy was HST＞GY602＞LC8275in IR treatment and HST＞LC8275＞GY602 (?)n RF treatment,competitive hierarchy wasdetermined by the below-ground competitive ability of cultivars,and competitive abilitymay have a negative relationship with the grain yield and WUE_G in monoculture.4.The results showed significant correlation between grain yield and above-ground biomass(r=0.94,P＜0.01),and WUE_G (r=0.95,P＜0.01),and a significant negative correlationbetween grain yield and the root:shoot ratio (r=0.81,P＜0.01).The yield superiority ofmodem and recent cultivars was mostly due to increased above-ground biomass,kernelnumber (r=0.96,P＜0.001) and WUE_G and a smaller proportion of root biomass.5.Our results demonstrate that inter-plant competition is an important factor affectingspring wheat productivity in contrasting environments,but the extent and intensity ofthese effects depend on the adaptation of root traits to available soil water.Reducing rootgrowth redundancy and enhancing the ability to deplete more soil water are clearlyadaptive features for wheat for water-limited conditions.The results of pot experiment shown as below,6.The grain yield of HST in control (no competition) were 13.20,6.23 and 2.27 g/plant atdifferent water regimes,which significantly higher than LC8275 (8.20,2.51 and 1.00g/plant)and GY602 (5.11,2.55 and 0.90 g/plant) (P＜0.05);inter-plant competitionespecially intra-cultivar competition reduced grain yield of the old cultivar significantlywhich were 1.97,1.31 and 0.69 g/plant in different water regimes,grain yield of targetplants in intra-cultivar competition for HST was the least in three cultivars,and the grainyield were 2.34,1.21 and 0.78 g/plant for GY602 and 2.28,1.43 and 0.88 g/plant forLC8275.7.The suppression effect was most intensity for HST and most weak for LC8275 in SWtreatment,biomass,root:shoot ratio,SRL and TRL were significantly differed betweendifferent competitive treatment for all cultivars (P＜0.05).With decreasing wateravailability,the plant biomass of old cultivar and intermediate cultivar were much moresensitive to competitive suppression than the modem cultivar,on the contrary,growthvarying in modern cultivar response only to water regimes.8.It appears that soil moisture is determining the plasticity of root responses of differentcultivars.Under water-deficit conditions,competition caused a significant increase in root shoot ratios for HST,and a significant increase in specific root length (SRL) for GY602and LC8275 for target plants compared to control plant (P＜0.05).9.Regression analysis showed old cultivar had a better and significantly linear relationshipbetween biomass and its allocation (r²=0.995,P=0.044;r²=0.999,P=0.018) under SWand MD treatments,as well as SRL (r²=0.999,P=0.00096;r²=0.999,P=0.0178;r²=0.998,P=0.028) and TRL (r²=0.9998,P=0.0095;r²=0.997,P=0.033;r²=0.999,P=0.023) under all three water regimes,whereas the intermediate and modem cultivarshad much more water-related species-specific changes in root morphology plasticity andallocation patterns.10.These results demonstrate that the suppression effect of inter-plant competition decreasedand the tolerance ability to competition increased through the wheat breeding process.Optimizations of adaptation ability with regard to competition and root morphologyplasticity to drought might be the key factcrs to maintain the yield gains in semiaridenvironment.Our study indicated that reduction of effect of inter-plant competitive suppression and rootsystem redundancy,and increasing of water use efficiency have the important implication toyield gain in semiarid regions.