Ecophysiology Responses And Proteomic Analysis Of Platycladus Orientalis Seedlings To Root Pruning

It is probably more adaptable to the stability of plant population and community of artificial forests,when they are established with seedlings of structure and function like natural forests.In vegetation restoration,excellent individual seedlings are optimum for rapid growth and successful establishment following transplantation.Root growth and development are the main determinants of the survival and establishment for transplanted seedlings.For an individual plant,root morphology and structure is crucial for plant adaptation to changing environments and plays a pivotal role in determining root functionality.However,root pruning must be considered as stress or damage to the seedling as it often perturbs root integrity when the seedlings are excavated from the nursery.The main objectives of the present study were to???investigate how root pruning would alter root morphology,and root responses further affect the ecophysiological adaptability of plant growth,???evluate the differences in the biomass allocation and root growth roots to air root pruning time,???assess how the root pruning time influences changes in the root morphology,physiology and anatomy of P.orientalis,???reveal the root physiological and proteomic responses to root pruning stress.These results are fundamentally important for its applicability to the current management practices in reforestation programs.Root damage and injury due to root pruning?RP?could impose stresses on individual seedlings,especially for transplanted plants.In this study,we investigated survival,root morphology,leaf photosynthesis and growth of P.orientalis seedlings that had been root pruned at four pruning intensities?0,?,? and ? of the taproots and accompanying fine roots were removed?.The unpruned treatment with intact taproot was the control?P₀?.Our results revealed that there were no significant differences in survival rate among the RP treatments for P.orientalis.The P_1/3 treatment significantly increased root length,the number of root tips,root surface area,root volume and specific root length of fine roots of P.orientalis?P < 0.05?.P.orientalis showed decreases in the photosynthetic rate,transpiration rate and stomatal conductance with increasing intensities of RP and pruned-seedlings had lower variables than the P₀?P < 0.05?.Likewise.All three RP treatments negatively affected the relative growth rate,specific leaf area,leaf dry weight,stem dry weight,root dry weight and total dry weight for P.orientalis.For P.orientalis,RP had no influence on the root to shoot ratios.The instantaneous water-use efficiency,leaf nitrogen concentrations,leaf carbon isotopic ratios and photosynthetic nitrogen use-efficiency of root-pruned seedlings for P.orientalis marginally decreased compared to the P₀.Overall survival and growth of P.orientalis responded differently to RP.Plant roots are important organs that function in the uptake of water and nutrients from the surrounding soil,and the physiological and morphological traits of roots affect shoot growth.Air-root pruning?AP?has been identified as an effective technique for enhancing root growth and development.However,little information is available regarding the temporal changes in the root system of P.orientalis under AP.The present study assessed the effect of air root pruning time on root morphology,biomass allocation,root absorption area and root anatomy of juvenile-stage P.orientalis seedlings,with non-root-pruned?NP?plants used as controls.The results indicated that there was a signifiantly increasing trend in root morphological parameters of P.orientalis seedlings in the AP treatment on day 10,30,50,120,150 and 190 d compared with the NP treatment,especially at 120,150 and 190 d?P < 0.05?.Root biomass,aboveground biomass,total biomass,root length,root surface area,root volume and root tip number all increased with air root pruning time.In addition,the total and active absorption areas of the roots significantly increased?P < 0.05?.AP significantly affected the biomass allocation pattern of P.orientalis seedlings?P < 0.05?,and the root:shoot ratio initially increased but then decreased,whereas it only decreased in the control.The diameters of most of the P.orientalis roots were 0-0.5 mm.Furthermore,AP improved the length,surface area,volume and tip number of 0-0.5 mm roots compared to the control,and the roots of this diameter range accounted for 79% of the total root tip number.The biomass and root characteristics of the P.orientalis seedlings were closely related.In addition to the average root diameter,the aboveground,root and total biomasses of the pruned seedlings were positively correlated to root length,surface area,volume and tip number.However,the root:shoot ratio and aboveground biomass were negatively correlated.Consequently,AP technology could be used to dramatically promote the growth and survival of P.orientalis seedlings by improving their root morphology and enhancing the absorption area of their roots during early growing stages.We performed integrated morphological,physiological and anatomical analyses of the roots in P.orientalis seedlings that had been air root pruned for 120,150 and 190 d.Our results found that the whole root length,number of root tips and root surface area of AP seedlings at 120,150 and 190 d were higher than those of the non-root-pruned?NP?seedlings?P < 0.05?,but the average root diameter did not differ significantly between the treatments.In comparison with the NP treatment,AP increased the root length,surface area,number of tips and specific root length of 0-0.5 mm diameter roots in P.orientalis during the experimental periods?P < 0.05?,but those of 0.5-1.0 mm diameter roots were only increased on day 190?P < 0.05?.The AP plants also exhibited higher root vitality and proportion of live fine roots than the NP plants?P < 0.05?.Based on the mean value across the three sampling times,differences were observed for root cross section,cortical thickness and stele diameter?P < 0.05?,while no differences were found in the stele to root diameter ratio among the different treatments.The AP seedlings had lower taproot lengths compared with the NP treatment at all sampling times?P < 0.05?.Although the cortical thickness of the taproot was similar between the AP and NP treatments during the first 120 days,it increased in AP at 150 and 190 d?P < 0.05?.However,for all three sampling days,the stele diameter of taproots did not differ significantly between the AP and NP treatments.Our anatomical evaluation of 0-0.5 mm roots and taproots revealed features that could account for the morphological differences found between the AP and NP plants.In conclusion,our results indicate that air-root pruning induced changes in the roots that promote the root system development in P.orientalis compared with the NP treatment during the experimental period.These results thus provide experimental evidence to support the use of AP in P.orientalis seedlings.The activities of POD and SOD as well as the contents of JA and ABA were found to be significantly higher in P.orientalis roots of RP than in the roots of NP at 6 h and 72 h.We used i TRAQ to perform a quantitative analysis of the roots of P.orientalis seedlings from RP and non-root pruning?NP?treatments.The proteomics analysis revealed that 5942 proteins were identified between RP and NP treatments at 6 h,72 h and 504 h,of which 678 proteins showed significant changes.And 271,360 and 106 proteins were differently expressed at 6 h,72 h and 504 h,repectively.Most of the differently expressed proteins were demonstrated to participate in the root responses of RP.These proteins included peroxidase,calreticulin-3-like,aquaporin,chitinase,heat shock protein,lipoxygenase and allene oxide synthase.GO functional category of 678 proteins indicated that they were associated with stress,denfense,hormone,signaling,metabolism,oxidoreductase activity and secondary metabolite biosynthetic process during the experimental process.The KEGG data indicated that these proteins involved in plant hormone signal transduction,glycolysis/gluconeogenesis,alpha-linolenic acid metabolism,transport and reactive oxygen species homeostasis.These results have important implications for understanding root physiological responses to RP and provide valuable information about the molecular traits of RP regulation of roots in P.orientalis.