| Populus spp.is one of the largest broad-leaved trees in China.And it has a variety of stress resistance and fast growth properties.However,in the past,for the genetic improvement of poplar and its large-scale popularization,the purpose was to consider the wood properties and yield.It has been rarely reported that whether the differences in the photoperiods of different climatic regions affected the popularization of poplar varieties.In this paper,29 Populus × euramericana seedlings were used as experimental objects.We isolated the exogenous light and then artificially controled light duration(LED full-spectrum plant growth lamp).There were five light treatments at 11 h,12 h,13 h,14 h and 15 h.Through the determination of the total biomass of 29 clone seedlings under different light time,screening for high light efficiency clones with biomass as the object was conducted using the normal distribution standard deviation classification.And measuring and analyzing Leaf length and leaf width,leaf perimeter and leaf area,petiole length,leaf shape index and specific leaf area,the number of leaves and relative water content,stomatal length and density on upper and lower surface of leaves,the root-shoot ratio,relative chlorophyll content(SPAD value),leaf photosynthetic response curve and photosynthetic characteristic parameters.The characteristics of chlorophyll fluorescence,survival rate,capping period and deciduous period of these selected clones.The physiological mechanism of its high light efficiency was initially revealed,providing new ideas for further study on the light-time adaptability of poplars.The main results of this study are as follows:1.The total biomass(35.51 g)of Populus × euramericana clones 11-28-11 was significantly higher than other clones under light of 11 h.Under light irradiation for 15 h,the total biomass of the clones 11-20-2 and the clones 11-26-7 reached 117.58 g and 118.32 g,respectively,and the total biomass of the seedlings as a whole showed an increasing trend as the light time increased.The coefficient of variation was greater than 35.60%.The accumulation of total biomass under different light time was similar to the normal distribution,and there was significant differentiation among the clones,indicating that different poplar genotypes responded to light conditions very differently,and genotype and environment interaction effects were significant.2.Under different light time treatments,the distributions of the total biomass distribution in the Populus × euramericana clones 11-28-11,11-20-2 and 11-26-7 were higher scored.The clones 11-36-23,11-45-6 and 11-40-2 have relatively lower scores.According to the scores of different clones in different light time,it was found that the accumulation of biomass was relatively good under the light intensity of the clone 11-28-11,and the clone 11-26-7 was relatively better under long light.Through the above researches,this study has initially screened 3 clones of Populus × euramericana with excellent total biomass accumulation and gene and light-time interaction effects(11-28-11,11-20-2,and 11-26-7)At the same time,select 3 clones with poor total biomass accumulation(11-36-23,11-45-6 and 11-40-2).3.The survival rate of the seedlings of Populus × euramericana was 80% under different light time.Extending the light time delayed the period of capping and defoliation of the seedlings,and the seedling height and ground diameter were improved.The clones 11-28-11,11-20-2,and 11-26-7 were most obvious under light irradiation for 15 h.The root to shoot ratio is less than 1,and photosynthetic products are preferentially supplied to the aerial parts.The correlation analysis showed that the relative increase rate of seedling height was significantly positively correlated with leaf length and width,leaf perimeter and single leaf area,petiole length and leaf number,and significantly positively correlated with the relative growth rate of ground diameter and total biomass.There was a significant negative correlation between leaf relative water content and specific leaf area.The relative growth rate of ground diameter was positively correlated with leaf number and relative growth rate of seedling height.There was a significant positive correlation between total biomass and seedling height relative growth rate and leaf number.There was a significant negative correlation with leaf length and leaf circumference.4.Under the light treatment of 11 h,the maximal SPAD values of the clones 11-26-7 were obtained.After the light time was greater than 14 h,the SPAD values of the clones 11-26-7,11-20-2,and 11-28-11 increased more significantly.At 11 h light exposure,the Pmax of the clone 11-26-7 was the largest,the LSP,Gs,Ci and Tr of the clone 11-40-2 were the largest,and the LCP and Rd of the clone 11-28-11 were the smallest,the WUE of clone 11-36-23 is the largest.Under light 12 h,the Pmax,Gs,Ci,and Tr of the clone 11-20-2 were the largest,the LSP of the clone 11-28-11 was the largest,the LCP and Rd of the clone 11-36-23 were the smallest,and the WUE was the largest.At 13 h of light,Pmax and LSP of 11-28-11 were the smallest in LCP and Rd of the clone 11-36-23,WUE of the clone 11-20-2 was the largest,and Gs,Ci and Tr of the clone 11-40-2 were the largest.Under 14 h light,Pmax,Gs,Tr and WUE of the clonal 11-28-11 were the largest,LCP of the clonal 11-28-11 was the smallest,LSP and Gs of the clonal 11-20-2 were the largest,Ci of the clonal 11-45-6 was the largest and Rd was the smallest.At 15 h of light,Pmax,LSP and Ci of the clonal 11-26-7 were the largest,WUE of the clonal 11-40-2 was the largest,LCP and Rd were the smallest,and Gs and Tr of the clonal 11-26-7 were the largest.The fluctuation range of Fv / Fm of Populus × euramericana clones was between 0.79 and 0.85 under different light time,indicating that the five light treatment time did not cause damage to the photosynthetic apparatus of Populus × euramericana clones. |
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