Response Of Robinia Pseudoacacia L. Seedlings To Soil Water Stress: Based On Growth, Physiology And The Allocation And Dynamics Of Non-structural Carbohydrates

Global climate change has posed a series of serious challenges to the earth ecosystem,not only in the continuous warming,but also in the frequent occurrence of extreme droughts and floods,and the stress intensity on the ecosystem is also increasing.Non-structural carbohydrates(NSC)play an irreplaceable role in the resistance to biotic and abiotic stress,especially in the resistance to water stress.At present,there is still a lot of uncertainty about the potential mechanism of NSC response to water stress.In this study,2-year-old Robinia pseudoacacia L.seedlings were repeatedly monitored in greenhouse for two years by using completely random block design.We studied the effect of different water-stress duration and water-stress intensity on the NSC allocation and dynamics of Robinia pseudoacacia seedlings.The water treatment intensity contained the field water capacity(FC,100%),extreme drought(ED,10%),moderate drought(MD,30%),control group(CG,70%)and waterlogging(WL,150%).At the same time,combined with morphology and some physiological and biochemical indicators to comprehensively explain the response mechanism of Robinia pseudoacacia seedlings to deficit soil water-stress(DSW)and excess soil water-stress(ESW).The main results and conclusions were as follows: compared with the control,except for MD promoted the increase of root dry weight and nodule dry weight and the later stage of WL increased root biomass.Water deficit DSW(ED and MD)and ESW(FC and WL)stress had different inhibitory effects on plant height,stem diameter,leaf area,total biomass dry weight and root nodule dry weight of Robinia pseudoacacia seedlings.Among them,the growth state under the control treatment was the best.At 30 days,the root nodule mass(RNM)and root nodule mass fraction(RNMF)under WL treatment reached the minimum,while the other indexes reached the minimum value under ED treatment.Under ED,theroot shoot ratio(RSR)increased at 10 d and then decreased,while that of MD and WL increased gradually(P<0.001).RSR had no significant change with time under control and field capacity treatments.Under CG treatment,the biomass reached the maximum at 30 days,and the biomass of whole-seedling,leaf,twig,stem and root increased by 42.5%,40.6%,67.4%,47.0% and 38.2%,respectively.There were significant effects of water deficit(DSW)and excess(ESW)on net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr),CO2 concentration(Ci),chlorophyll content(Chl),Leaf nitrogen content(leaf nitrogen,LN),leaf relative water content(LRWC)and leaf water use efficiency(LWUE)of of Robinia pseudoacacia seedlings.Especially under DSW treatments,Chl and LN had no significant change under ESD treatments,and Chlb was more sensitive to drought stress than Chla,resulting in a significant increase in Chla/b under drought stress.At 10 days,the photosynthetic ability of Robinia pseudoacacia seedlings was limited by ED,MD,FC and WL,and the average value of Pn decreased by 83.0%,60.2%,333% and 70.1%,respectively.Under the treatment of ED for 30 days,the values of Pn,Gs,Tr,(Chlt),LN,LRWC and LWUE of Robinia pseudoacacia seedlings reached the lowest in two years.The two-year average decreased by 96.0%,86.8%,93.3%,74.4%,51.8%,91.3% and 66.9%,respectively.There were significant effects of DSW and ESW on total non-structural carbon(TNSC),soluble Sugars(SS),starch(Sta),fructose(Fru),Glucose(Glu)and sucrose(Suc)in whole-seedling and tissues and the ratio of above-and below-ground(RAB)of Robinia pseudoacacia seedlings.After 10 days of treatment,DSW and ESW increased the content of TNSC and SS and decreased the content of starch in the whole plant and the four tissues.Compared with the initial value,the content of TNSC and SS increased at 10 d and then decreased under ED and WL treatments,and there was weak fluctuation under CG and FC treatments.At the same time,ED,MD and WL decreased the RAB of TNSC,SS,Fru,Glu,Suc and Sta,while FC treatment increased the RAB and there was instability in them.The trends of fructose,glucose and sucrose were similar,but the content of glucose was relatively low,and it was more sensitive to drought stress,and there was a strong positive correlation between starch content and photosynthetic rate and biomass.Compared with the control group,both ED MD FC and WL showed an upward trend at 10 d in two years,especially under the treatment of ED.The average content of TNSC and SS in the whole plant was 1.8 and 3.1 times higher than that of the 0 days under ED,respectively.While the starch content decreased by 53.6%.At 30 days,the starch content reached the minimum,which decreased by 66.0%,and there was no depleted phenomenon in TNSC,SS and starch.From the analysis of the correlation between NSC and other indexes,it can be concluded that NSC and its components have a close potential relationship with growth and physiology.Under water deficit and excess,the ratio of soluble sugar content to starch content(RSR)increased at 10 d and then decreased under ED,MD and WL.After 10 days of ED treatment,the RSS in whole-seedling,leaf,twigs,stem and root increased by about 6,32,5,3 and 12 times compered to the initial values,respectively.There was a negative correlation between soluble sugar and starch in the whole-seedling and tissues,and the strongest at 10 days.The effect extent of water deficit is greater than that of excess water.The response characteristics in growth,physiology and biochemistry,NSC and its components in the whole-seedling and tissues were asymmetrical,and the larger increment occurred under DSW treatments.The results showed that Robinia pseudoacacia seedlings may adopt different adaptation strategies under different water stresses,in which starch may be transformed into soluble sugars to resist different intensity and short-term persistent water stresses.To sum up,this study provides a unique perspective and valuable information,such as the transformation between soluble sugars and starch,as well as the allocation and dynamic characteristics of NSC and its components in the whole-seedling and different tissues.Combined with the indexes of growth and physiological and biochemical of Robinia pseudoacacia seedlings.It provides a theoretical basis for further elucidating the allocation and dynamic mechanism of plant NSC under short-term persistent drought and waterlogging.Our next step is to consider how and to what extent plants use NSC to cushion the corresponding water stress and maintain normal metabolism.The allocation and dynamic characteristics of growth,physiology and NSC in different tree species,diurnal variation and different seasonal patterns were need to be compared and combined.