| Non-hydraulic root-sourced signal（nHRS）is the only positive and active response in crops to drought stress so far.It plays a key role in regulating water use efficiency,individual size,crop growth and energy allocation,but the internal laws and governing mechanisms are still unclear.Based on allometry theory and root-shoot communication theory,wheat with different ploidy（2n,4n and 6n）and different domestication degree（primitive wheat and modern wheat）were selected as an experimental material.In order to analyze and compare the characteristics and differences across the relationship between yield formation and allometric growth materials and to explore the mechanism of wheat yield formation in dryland under the regulation of non-hydraulic root signals and different planting densities of different wheat genotypes,we used pot-culture experiments and field experiments.These experiments consisted of different water gradients and planting densities to determine the growth,gas exchange parameters,biomass distribution,yield forming components and related physiological and biochemical indicators.The major results were presented as follows:1.Non-hydraulic root-sourced signal induction and grain yield performance of different ploidy wheatNon-hydraulic root-sourced signals in different ploidy wheat were induced and yield indices were determined by alternate water supply with pot-culture experiment.The data showed that compared to well water supply group（CK,80%Field Water Content）,the stomatal conductance in the drought treatment group decreased significantly,the ABA content of leaves increased significantly while the relative water content of leaves did not significantly change,so the non-hydraulic root-soured signals were identified.Under well water supply,the grain yields of diploid wheat MO1 and MO4,tetraploid DM31 and DM22,hexaploid HST,DX24,L8139 and L8275 were 1.45,1.15,2.74,2.93,3.58,3.34,3.27 and 3.03 g/plant,respectively.Under the control of nHRS,the grain yields of the above wheat varieties were 0.78,0.81,2.03,2.19,2.35,2.48,2.23 and 2.17 g/plant,respectively.The diploid reduced the most,whereas the tetraploid and hexaploid had the highest grain yield retention rate.The results show that under the regulation of nHRS,wheat yield decreased,where diploid wheat was the most affected.With the increase of ploidy,the yield per plant increased gradually.2.Growth,water use and yield formation characteristics of different genotypes of wheat under non-hydraulic root-sourced signalUnder the control of nHRS,plant height and leaf area in different genotypes of wheat showed a decreasing trend.The specific leaf area and root-shoot ratio in different genotypes of wheat changed differently.The specific leaf area of primitive wheat did not change significantly but the specific leaf area of modern wheat decreased significantly.The root-shoot ratio in MO1 decreased considerably.The root-shoot ratio in other genotypes of wheat did not change significantly.The yield and biomass of different genotypes of wheat decreased,especially in diploid wheat.The harvest index of different genotypes of wheat changed differently.The harvest index of DM22 and HST did not change markedly,while the harvest index in other wheat genotypes decreased significantly.Water use efficiency in different genotypes of wheat increased under the regulation of non-hydraulic root source signals.The results showed that the plant height,leaf area and biomass of wheat genotypes decreased significantly under the control of non-hydraulic root signals,and the diploid wheat decreased the most,and the water use efficiency increased significantly.3.Allometric relationship between biomass allocation of modern and primitive wheat under non-hydraulic root-sourced signalThe various organs biomass and aboveground biomass of both primitive（brittle ears,hard to threshing）and modern wheat（non-brittle ears,free-threshing）showed a significant power function relationship（P<0.001）.Under the control of nHRS,for the primitive wheat,the R-V index of primitive wheat increased significantly from1.420 to 1.812,the allometric index of spike increased significantly from 1.232 to1.398,which was significantly greater than 1,the allometric relationship of leaves did not change significantly between two treatments,the allometric index of stem decreased significantly from 1.141 to 0.957.However the allometric index of R-V,spike,leaf and stem in modern wheat had no significant difference.The results showed that the reproductive efficiency of big individual was higher than that of small individual in primitive wheat,while that of modern wheat showed an isokinetic growth,and the reproductive efficiency remained unchanged,under the control of non-hydraulic root signals.The stem allometric index of primitive wheat decreased significantly,while that of modern wheat did not change significantly.Primitive wheat regulates reproductive allocation through stem changes,while modern wheat maintains stable yield through stable vegetative biomass allocation.The various organs biomass and total biomass of both primitive and modern wheat showed a significant power function relationship（P<0.001）.Under the control of nHRS,for the primitive wheat,the allometric index of spikes increased significantly from 0.945 to 1.048,while that of modern wheat decreased from 0.885 to 0.876,but there was no significant difference between them.There was no significant change in the allometric index of the leaves and total biomass of both primitive and modern wheat,and the allometric indices were greater than 1.The allometric index of root biomass of primitive wheat increased significantly from 0.952 to 1.159,while that of modern wheat increased from 1.291 to 1.315,but there was no significant difference between them.The allometric index of root and leaf of primitive wheat increased significantly from 0.779 to 0.968,while there was no significant difference between modern wheat.The results showed that,under the control of nHRS,with the increase of individuals,the proportion of root biomass allocation of primitive wheat was larger than that of leaf biomass allocation,and the relationship of root biomass vs.total biomass and root biomass vs.leaf biomass did not change in modern wheat.The allometric index of stem and total biomass of primitive wheat decreased significantly,that is,large individual distributed less biomass to stem,small individual distributed more biomass to stem,while that of modern wheat did not change.Primitive wheat regulates reproductive allocation by changing the relationship between root,leaf and stem,while modern wheat maintains stable yield through stable vegetative biomass allocation.4.Allometric relationship between main growth phenotypes and individual size of modern and primitive wheat regulated under non-hydraulic root-sourced signal operationThe main growth phenotypes biomass and aboveground biomass in both primitive and modern wheat showed a significant power function relationship（P<0.001）.Under the control of nHRS,the allometric index for leaf area and aboveground biomass in primitive wheat increased significantly from 1.007 to 1.382.There was no significant change in modern wheat,with index 1.438 and 1.75,respectively,which were the allometric growth relationships with index greater than 1.The allometric index of plant height and aboveground biomass in primitive wheat decreased significantly from 0.585 to 0.423.The SLA allometric index of primitive wheat increased significantly from-0.806 to 0.532,while that of modern wheat did not change significantly,with indices of-1.002 and-1.864,respectively.The allometric index of spike and leaf area of primitive wheat decreased significantly from 1.33 to1.069.There was no significant change in two water treatments of modern wheat,the index was 0.788 and 0.685,respectively,which were both isometric growth relationships with index less than 1.The results showed that the primitive wheat individuals increased their competitive ability to obtain more resources by increasing biomass input in leaf area and plant height,while the allometric growth index of modern wheat did not change significantly,which ensured its stable growth pattern.5.The allometric relationship between primitive wheat and modern wheat under different densities（field experiment）The various organs biomass and aboveground biomass of both primitive and modern wheat showed a significant power function relationship（P<0.001）.Under high density conditions,the allometric index of the leaves of the primitive wheat decreased significantly from 1.082 to 0.962,and that of modern wheat decreased significantly from 1.177 to 0.903.The allometric index of primitive wheat stem was1.077 at low density,which was significantly higher than high density（1.008）.The allometric index for stem in the modern wheat was 1.088 at low density,which was significantly lower than at the high density（1.173）.The allometric growth of primitive wheat spike was 1.077 at low density,which was significantly lower than1.165 at high density.The allometric index of modern wheat spike and aboveground biomass at low density and high density was 1.032 and 1.061 respectively,and there was no significant difference between them.The results showed that,for the primitive wheat,with the increase of density,the source strength of the small individuals increased,and they allocated more biomass to stem,which led to the decrease in biomass allocation in spike.With the increase of density,the source strength of small individuals in modern wheat increased,and the biomass allocation to stem decreased,so that the proportion of reproductive allocation did not change.6.The allometric relationship between primitive wheat and modern wheat under different densities（pot-culture experiment）The various organs biomass and total biomass of both primitive and modern wheat showed a significant power function relationship（P<0.001）.The allometric indices of primitive wheat spikes under low density and high density were 1.117 and 1.149,respectively,and there was no significant difference between them.The allometric indices of modern wheat were 1.079 and 1.201,respectively,and the high density was significantly higher than that of low density.The allometric index of primitive wheat leaves was 1.064 and 0.909 under low density and high density,respectively,while that of modern wheat was 1.269 and 0.784,respectively,and the high density was significantly higher than that of low density.The allometric index of primitive wheat roots was 1.099 and 0.895 under low density and high density,respectively,which decreased significantly,while that of modern wheat was 1.009 and 0.929,respectively,with no significant difference.There was no significant difference in the stem allometric index between low density and high density conditions of the primitive wheat and the modern wheat.The allometric indices of primitive wheat leaf area and total biomass under low density and high density were 1.021 and 0.930,respectively,and there was no significant difference between them.The allometric indices of modern wheat were 1.203 and 0.749,respectively,and the low density was significantly higher than that of the high density.The results showed that primitive wheat had larger root,while modern wheat had higher aboveground part（it had higher plant height,larger leaf area and larger leaf sheath）.This also indicates that the competition center of wheat had shifted from the underground part of primitive wheat to the aboveground part of modern wheat.The underground competition intensity in primitive wheat population is higher than that of modern wheat,and the aboveground competition intensity is lower than that of modern wheat.In the process of wheat domestication,the intraspecific competition center of wheat shifted from underground to aboveground.7.The allometric mechanism of dryland wheat yield formationBy calculating the derivative,we could get the derivative equation of Y=βXα,that was Y’=αβXα-1.Whenα>1,the change rate of Y value increases with the increase of X,while whenα<1,the change rate of Y value decreases with the increase of X.Whenα=1,the proportion of biomass allocated to the corresponding organs did not change with the size of the individual.It can be concluded from the above results,under the control of nHRS the allometric index of the spike and root increased,the leaf did not change,the stem decreased,which indicated that the biomass allocation of the large individuals in spike and root was larger than that of small individuals,in stem was less than the small individuals.By increasing the growth of vegetative bodies of large individuals,primitive wheat has stronger individual competitiveness,can obtain more resources in the population,and produce more reproductive bodies to ensure population reproduction.The allometric relationship of different phenotypes and biomass allocation of modern wheat has not changed,so it has a more stable biomass allocation pattern.At the same time,the biomass allocation of the small individuals in spike was larger than that of the larger individuals,which ensures that small individuals can complete reproductive growth and ensure stable output of population yield when resources are limited.Under high density,the allometric index of leaves and stems in primitive wheat decreased and in spikes increased.The results showed that small individuals increase biomass allocation to leaves and stems,but decrease biomass allocation to spikes.It may increase their survival ability but reduce reproductive capacity.The allometric index of leaves decreased,while stem increased and spikes remained unchanged in modern wheat,indicating that small individuals increased biomass allocation to leaves and decreased biomass allocation to stems,and the biomass allocation to spikes remained unchanged.So that it can reproduce steadily.Based on the response by different organs of primitive wheat and modern wheat to nHRS and different planting densities,the resource allocation patterns of large and small individuals in response to different external environments during wheat domestication were studied.When resources are limited,primitive wheat guarantees maximum reproduction by increasing the competitive advantage of large individuals,while modern wheat guarantees population output by stable reproductive allocation. |
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