| Since Donald firstly proposed the concept of “ideotype” in 1968,crop plant-type improvement based on physio-ecological traits has been well developed in wheat breeding.Many agronomists and breeders have endeavoured to reduce growth redundancy and improve the ideotype of crops,and have made some progresses on improving the crop population production.Nevertheless,the current researches always lack of the systematic “big data” analysis and targeted verification studies on the evolution of physio-ecological traits and the drought adaptation mechanisms.Furthermore,a variety of matrials,drought treatments and growth environment were selected in different researches,which resulted in various or even contrary experimental results.Therefore,a comprehensive research to address these fundamental scientific questions mentioned above is highly demanded.In order to study wheat physio-ecological traits evolution,biomass allocation,competitiveness,yield formation,and the mechanism behind its adaptation to drought stress during evolution,we conducted our research based on the meta-analysis and growth environment controlled verification tests.Meta-analysis was conducted by collecting published data worldwide,and then selecting 303 papers based on the criterion,building the database and analyzing integratedly.Growth conditions controlled experiments were conducted to verify the results of some representative traits' evolutionary trends from meta-analysis.The aims of pot-culture trails included: 1)Discover the physiological and biochemical responses of wheat species differing in ploidy level,together with their wild relatives,and their biomass allocation model to drought stress;2)Study the relationships between competitiveness,yield and biomass allocation in different wheat species during its domestication through de Wit replacement series experiment.We conducted the field trial aimed to study the characteristics of wheat plant type,yield,water use efficiency,size hierarchy,biomass allocation and its adaptation mechanisms under different ridge-furrow mulching treatments.The major results were presented as follows:1.Meta-analysis results of wheat physio-ecological traits characteristics during evolution.1)The difference of growth parameters reduction caused by drought stress was compared among all ploidy levels.Results showed that the hexaploid(6n)wheat had the highest biomass and yield retention.Grain yield was reduced by 53%,42% and 39%;aboveground biomass was reduced by 42%,42% and 27%;while the root biomass was reduced by 14%,16% and 29% in 2n,4n and 6n levels,respectively.Under drought stress,the reduction of aboveground biomass of 2n and 4n wheat was greater than that of 6n wheat,while the reduction was similar between aboveand below-ground biomass in 6n wheat.Results showed that different ploidy wheat allocated their biomass differently under drought stress.The 6n wheat that has went through the domestication and artificial selection processes optimized biomass allocation pattern and reduced the growth redundancy,which is the basic of improving wheat yield production.2)The reduction in thousand kernel weight(TKW)and the seed number per plant(SN)were affected by the wheat ploidy levels,spring/winter types and growth conditions.Moreover,there was a trade-off relationship between the TKW and SN.The TKW was reduced by 21%,12% and 16%;SN was reduced by 54%,29% and 16% in 2n,4n and 6n levels,respectively.The 2n wheat had the greatest reduction in both TKW and SN under drought stress.In addition,drought stress had much more effects on SN and TKW in the pot-culture conditions than that in field conditions,and spring wheat was much more affected than the winter wheat.The SN–TKW relationships of higher ploidy wheat species were optimized by domestication,and these higher ploidy wheat species maintained higher yield retention under drought stress.Results indicated that the relationships between the SN–TKW were various under different ploidy wheat.3)A relatively higher leaf area retention and tiller number reduction is benefit for the improvement the yield production.Under drought stress conditions,tillers number was reduced by 15%,18% and 26% and leaf area was reduced by 73%,50% and 30%,in 2n,4n and 6n levels,respectively.For 6n wheat,the tillers number had the greatest reduction while the leaf area had the smallest decline under drought stress.Results demonstrated that leaf area is one of the most important factors which affect the yield production,and it has a relatively higher retention in 6n wheat.Furthermore,the 6n wheat reduced the growth redundancy by decreasing the tillers number,optimized the plant types and then had higher yield retention under drought stress.4)The osmolytes,membrance lipid peroxidation parameters and the gas exchange parameters were significantly changed under drought stress.The photosynthesis rate(Pn)was reduced by 40%,65% and 33%,stomatal conductance(gs)was reduced by 56%,74% and 63%,and the intercellular CO2 concentration(Ci)was reduced by 9%,14% and 38% in 2n,4n and 6n levels,respectively.The soluble sugar concentration increased by 90%,120% and 35%;proline concentration increased by 274%,493% and 213%,and MDA increased by 125%,95% and 80%, in 2n,4n and 6n levels,respectively.Results showed that as for the biochemical parameters,2n and 4n wheats had a greater increase than that in 6n wheat,and the reduction in gas exchange parameters in 2n wheat was higher than that in 4n/6n wheats.Besides,the lower ploidy wheat was much more affected by drought stress than the higher ploidy wheat,and the wheat in pot-culture conditions was much more sensitive to drought stress compared with those in field conditions.2.Response of physio-ecological traits in different ploidy wheat on drought stress in pot-culture conditions and the verification of its regulatory mechanism.5)The trade-off relationship was found between the seed number and seed size under domestication process by comparing the yield,yield components and morphological traits of 8 wheats cultivars under drought stress.The seed number and seed size showed a decreasing trend in all wheats under 50% and 25% FC conditions,and this is supported by meta-analysis results.The relationship between seed number and seed size showed a positive correlation in cultivated 2n wheat(R2 = 0.33,P < 0.01);for the 4n/6n wheat species,there was a negative correlation between the seed number and seed size(R2 = 0.45,P < 0.01).Further analysis showed that the cultivated 2n wheat is source-limited,and the 4n/6n wheat is sink-limited.The results demonstrated that the sink–source relationship was changed during the wheat evolution.Some of these pot-culture experiment results agree with meta-analysis results.6)Drought stress significantly increased the chemical parameters in all wheat species,while decreased the gas exchanged parameters.Under drought stress,the MDA accumulated more in cultivated wheats than that in wild wheat,and MDA and proline accumulation in 4n/6n wheat was higher than that in 2n wheat.The gas exchanged parameters such as gs was more sensitive to drought stress at anthesis,while the RWC showed the opposite trend.Results showed that the wheat is more sensitive to drought stress at anthesis,and it can quickly adapt to the drought condition through altering the physio-ecological traits.On the other hand,at anthesis,the RWC can still keep a relative higher level in 4n/6n wheats,which implied that the higher ploidy wheat has adapted to drought stress after domestication and artificial selection.These results partly supported and complemented the meta-analysis results,and this shows a complex response of different wheats under the drought stress.7)Drought stress significantly increased the root-to-shoot(R:S)ratio in all ploidy levels.The R:S ratio in 2n wheat was significantly higher than that in 4n/6n wheat.Analysis of the allometric relationships between aboveground biomass(MAB)and root biomass(Mroot)at different ploidy levels indicated that less biomass was allocated to roots under domestication while more biomass was allocated to roots with drought in the wild 2n species,but not in the domesticated species.We concluded that evolution under domestication of higher ploidy wheats has increased wheat yields primarily by increasing harvest index(HI),to a greater extent than aboveground biomass' increases that were maintained under water stress.The yield increase was mainly because more biomass was allocated into the ear parts,and this increase rate was greater than that in aboveground parts,thus enhanced the HI.These results supported the meta-analysis results.3.Verification test on relationship between wheat yield and its competitiveness in pot-culture conditions based on de Wit replacement series experiment.8)At 2n level,cultivated wheat(MO1)produced more seed biomass than the wild wheat(BO1)in well watered conditions under both monoculture and the mixture 2:2 of MO1 and BO1.The input-output ratio results showed that MO1 was a stronger competitor.Under drought stress,BO1 had greater yield production and stronger competitiveness in both monoculture and mixture conditions.At 4n level,the seed biomass of cultivated wheat(DM22)was greater than that of wild wheat(DS10)in well watered conditions(P < 0.05)in both monoculture and the mixture 2:2 of DM22 and DS10.Compared with DS10,DM22 produced much more seed biomass under drought stress in both monoculture and mixtures conditions,while due to more seed number were produced,DM22 was more competitive according to the input-output ratio results.Results showed that there was no clear relationship between the competitiveness and the yield.Furthermore,the competitiveness could be reversed due to changing environment.While the cultivated wheats with the artificial population characteristic,had weaker competitiveness under well water conditions,which is benefit for yield increase.9)At 6n level,for the old(DX24)and modern wheat cultivars(LC8275),the seed biomass of LC8275 was significantly higher than that of the DX24 in monoculture in both well watered and drought stress conditions.While at 2:2 mixture condition,DX24 had higher seed biomass than that of the LC8275.Moreover,DX24 had stronger competitiveness in any water conditions.Results showed that modern wheat cultivars had a weaker competitiveness and higher seed biomass.And there was a negative relationship between the competitiveness and the yield production in the higher domesticated level wheat species.All of these implied that domestication and artificial breeding weakened the competitiveness,reduced the growth redundancy,optimized the biomass allocation,and improved the population yield production.It is beneficial to ideotype building.4.The yield and yield formation,morphological plasticity and biomass allocation in two hexaploid wheat cultivars under ridge-furrow mulching farming system.10)Ridge-furrow mulching farming system significantly reduced the evapotranspiration and ineffective tillers number while increased the plant height(13–38%),leaf area(28–108%),yield(74–163%),aboveground biomass(36–104%),water use efficiency for grain(88–271%)and harvest index(13–44%),respectively.There was a negative correlation between the harvest index and the Gini coefficient(represents the size hierarchy of aboveground biomass).Results showed that ridge-furrow farming system could improve the wheat physio-ecological traits,reduce the individual size hierarchy and growth redundancy,and weaken the competitiveness.Ridge-furrow mulching treatments could affect the allometric relationship between the vegetative(V)and reproductive(R)parts,which means more biomass was allocated into the ear parts,and resulted in the higher harvest index.This farming system optimized the biomass allocation.The above results supported the meta-analysis results.To some extent,it explained the influence of growth redundancy and competitiveness on the population yield production.11)Extensive research showed that ridge-furrow mulching farming system could prolong the growth periods and improve the soil quality in two growing seasons.Under the mulching treatments,the growth period of Lin Mai and DUMA was prolonged 5.2 and 8.7 days,respectively.Grass-straw mulching could significantly increase soil organic carbon content.Compared with ridge-furrow film mulching(RFF)and control(CK)treatments,soil total nitrogen(STN)in ridge-furrow grass-straw mulching treatment(RFS)were increased by 5.3–10.1%.Results showed that mulching treatment could significantly prolong the growth period,especially the reproductive stages;it is an important factor to increase the wheat yield and biomass accumulation.On the other hand,mulching treatment can improve the micro-environment conditions.RFS not only has similar yield increase effects with RFF but is also low-cost and environmental friendly,which is benefit for the sustainable development of local agriculture.Based on the meta-analysis of different ploidy wheat's responses to the drought stress,we concluded a general rule about the changes of morphological,physio-ecological traits and biomass allocation during the wheat evolution.The analysis of the wheat adaptation and regulation mechanisms to drought stress during its evolution also provided new theoretical potential for the field of crop ecology and evolution.We also tested the meta-analysis results by pot-culture and field experiments,and the results of pot-culture and field experiments partly supported the meta-analysis results,implying the complex phenomenon of different wheats' response to drought stress.In this study,one field experiment was conducted to compare the morphological traits and biomass allocation of different wheat cultivars under different mulching treatments.It indicated that the reduction of growth redundancy is an important aspect for dryland wheat breeding,especially in ideotype breeding.It is meaningful for researchers to understand the mechanism of wheat adaptation to environment,and is useful for future breeding programs. |
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