Effects Of Root Modification On Water Use And Yield Formation And Its Eco-physiological Mechanism In Dryland Wheat

The phenomenon of root redundancy is a basic scientific question in the field of crop ecology and system evolution.The magnitude and structure of root system play great affects on growth,water use,biomass allocation and yield formation in dryland wheat.Though the preliminary trail had been done on this phenomenon by the method of root modification,there is still limitation in this method.Much work should be done to clarify the mechanism of root to shoot communication which is still unclear.Based on the theory of growth redundancy in crops,we applied different methods of root modification and controlled water condition in containers to find out how root system affect water use and yield formation and its eco-physiologically mechanism in dryland wheat.This study was performed in Yuzhong experimental station of Lanzhou University from 2013 to 2015.Two cultivars were selected for this study based on their specific growth performance,one was Heshangtou(HST),an old cultivar with relatively larger root system,and the other one was Longchun8275(LC8275),a modern cultivar with relatively smaller root system.The pot and pipe experiments were applied in this study with cutting root in different degrees and directions to modify root systems.The measurements such as grain yield,water use efficiency and regulation of root-sourced signals were determined in this study.The main results were as follows,1.Effects of different root architectures on water use and grain yield in wheatIn 2013,three different root architectures containers were used to modify the root system of spring wheat LC8275 so that three different root architectures were induced as follows,lateral growth,balanced growth and longitudinal growth.Two water conditions were controlled,one was well water,and the other was alternate partial root-zone irrigation.The results showed that grain yield was significantly decreased in longitudinal growth group(8.29 g/pot)compared with lateral growth group(18.21 g/pot)and balanced growth group(19.77 g/pot)in well-watered condition.As for water consumption,lateral growth group(20.31 kg/pot)was the highest while longitudinal growth group(9.37 kg/pot)was the lowest.Moreover water use efficiency for grain yield had no significant difference in these three different root architectures(0.89 g/kg,1.14 g/kg and 0.89 g/kg).Likewise,water use efficiency for shoot biomass was lower in lateral growth group(2.83 g/kg)than in other two groups(4.16 g/kg and 4.30 g/kg).In addition,the similar results were showed in alternate partial root-zone irrigation condition,but there was no significant difference in root-sourced signals under both water conditions.Therefore,LC8275 had higher grain yield consuming relatively little water under balanced growth,showing the potential of high yield and water saving.2.Effects of serious root pruning on water use and grain yield in wheatIn 2014,a pot experiment was conducted using the method of root pruning in spring wheat LC8275.Three water conditions were applied,well water,moderate drought stress and alternate partial root-zone irrigation.The results showed that root pruning did not significantly alter water use efficiency for grain yield(1.07 g/kg,0.91 g/kg and 0.97 g/kg)compared to control(1.14 g/kg,1.10 g/kg and 0.95 g/kg).There was also no significant difference in water use efficiency for shoot biomass after cutting root(P>0.05).As for grain yield,root pruning significantly decreased grain yield from 23.65 g/pot to 17.10 g/pot of LC8275 under well-watered condition,but had no significant effects under moderate drought stress(11.37 g/pot and 14.95 g/pot)and alternate partial root-zone irrigation(9.03 g/pot and 9.72 g/pot).It was also find out in our results that different values in alternate partial root-zone irrigation group(0.72 g/pot)was smaller than in well-watered group(6.55 g/pot)and moderate drought group(3.58).The result of leaf abscisic(ABA)and zeatin riboside(ZR)content showed that there was significant difference between control and root pruning group only under alternate partial root-zone irrigation.Therefore,alternate partial root-zone irrigation could regulate root-sourced signals to relieve the effects of root pruning on growth and grain yield of wheat.3.Effects of vertical root pruning on water use and grain yield at different stagesIn 2015,a pot experiment using two spring wheat HST and LC8275 as materials was conducted under both well-watered condition and moderate drought stress.In this experiment,pruning root were performed vertically in different degrees at jointing stage and booting stage respectively.The results showed that two-side root pruning decreased grain yield of HST under well-watered condition.There were no significant difference on grain yield of HST between root pruning groups and controls after one-side root pruning.Both under well-watered condition and moderate drought stress,root pruning had no significant change on grain yield of LC8275.In this experiment,root pruning did not affect water use efficiency of LC8275 and HST.From the perspective of root growth redundancy,there was root redundancy in horizontal direction in spring wheat,and the degree of root redundancy was related to genotypes and water conditions.4.Effects of horizontal root pruning on water use and grain yieldIn 2015,a PVC pipe experiment using spring wheat HST and LC8275 as materials was conducted under both well-watered condition and moderate drought stress.In this experiment,pruning root was done horizontally at jointing and booting stage respectively.The results showed that horizontal root pruning significantly changed grain yield in HST from 9.77g/pot to 7.78g/pot and 8.37g/pot under well-watered condition,but did not significantly change grain yield in HST under moderate drought stress(5.13g/pot and 5.77g/pot)compared to control(5.30g/pot).The grain yield in root pruning groups were 7.09 g/pot and 7.66 g/pot in LC8275,having no significant difference compared to control(7.75 g/pot)under well-watered condition.These results were similar under moderate drought stress in LC8275.As for water use efficiency,the results showed that horizontal root pruning decreased water use efficiency of HST under well-watered condition from 1.70g/kg to 1.53g/kg and 1.53g/kg.But water use efficiency(1.83 g/kg)of HST increased when cutting root at booting stage compared to control(1.68 g/kg)under drought stress.However water use efficiency of LC8275 was not affected by horizontal root pruning.From the perspective of root growth redundancy,there was root redundancy in vertical direction in spring wheat,and the degree of root redundancy was related to genotypes and water conditions.5.Effects of root pruning on regulation of root-sourced signalsIn 2015,a gradually drought experiment using spring wheat LC8275 was conducted to explore the effects of root pruning on regulation of root-sourced signals.Root for plants were cut at jointing stage and natural drought began at flowering stage.The results showed that non-hydraulic root-sourced signal(n HRS)soil water threshold range of LC8275 was 77.80-46.59% field water capacity(FWC)in root pruning group,broader than 71.88-47.89% FWC in control group.It indicated that n HRS was triggered earlier after root pruning.Though there was no significant difference on lethal leaf potential,Lethal leaf water potential in root pruning group(-2.70 MPa)decreased compared to control group(-2.19 MPa),which indicated that root pruning could enhance drought resistance capacity of spring wheat.6.There were a strong spatial-temporal and genotypic dependence regarding the effects of different root pruning on grain yield and water useThe results of correlation analysis between root biomass and grain yield showed that there was a significant correlation between root biomass and grain yield.Effects of root pruning on root biomass and grain yield had strong specificity of space and time,which might be caused by different methods of root pruning.In our research,we observed that the effects of two-side root pruning were more serious than one-side root pruning under similar degree of root pruning.Furthermore,HST with a relatively larger root system was more sensitive to root pruning compared to LC8275.The growth and grain yield of spring wheat could be regulated by root modification related to root architecture and root magnitude.Comparing the results from the experiments in 2014 and 2015,it was found that root pruning decreased grain yield under well water more often,but had no significant change under moderate drought stress.It is also found that the phenomenon of root redundancy occurred more under drought stress.From the perspective of genotype,the occurrence of root redundancy existed in the cultivar with larger root system.And root system redundancy of spring wheat existed in both horizontal and vertical directions.