The Relationships Between Poplar Hydraulic Traits And Growth Rate As Well As Biomass

In the context of the current development of sustainable forestry,it is very important to breed high-yield tree species.Since the water transport capacity of the xylem greatly affects the process of plant biomass accumulation,hydraulic traits may be used to reflect the high yield potential of the tree species.In order to apply hydraulic traits to the rapid breeding of highyield tree species,it is critical to study on the relationship between hydraulic traits and growth rate as well as biomass.In this study,nine I-101(Populus alba)× 84K(P.alba × P.glandulosa)poplar clones with differences in growth potential were selected,and the hydraulic efficiency(stem-segment,shoot,root,and whole-plant)and growth(aboveground biomass andgrowth rate)were measured for three consecutive years.The relationships between hydraulic efficiency of each level and growth,and its stability on the time scale,were analyzed.The hydraulic resistance of each organ and its distributions were quantified.The influence of hydraulic efficiency on the gas exchange process of leaves was explored by measuring gas exchange and leaf water potential.At the same time,the relationship between hydraulic safety and biomass was found by measuring the hydraulic safety of branches and the xylem anatomical structures,and the characteristics of xylem vessels and pits that determine the growth and hydraulic characteristics were found.The main conclusions are as follows:(1)the nine clones showed significant differences in aboveground biomass and growth rate in three years,and the growth differences can be maintained steadily over years.The hydraulic efficiency at the stem-segment level of each clone changes significantly over years,in contrast,most clones can maintain a stable hydraulic efficiency at the larger level(shoot,root,and whole-plant).There was a positive correlation between the hydraulic efficiency at each level and the aboveground biomass and growth rate,but the correlation at the stem-segment level was only significant in the first year,while the correlation at the larger level can remain significant for three years.In addition,the ability of the hydraulic efficiency at the stemsegment level to reflect the hydraulic efficiency of the whole plant was weakening over years.(2)there were significant differences in the hydraulic resistance of each organ of the nine clones,but the distribution difference of the resistance was relatively small.The root hydraulic resistance accounts for the largest proportion,but it was close to the aboveground resistance.Among the aboveground resistance,the resistance of stem and leaves were similar,and the resistance of petioles only accounts for about 3% of the whole plant.Most of the resistance of the stem was distributed in the main bole,and the resistance of the curren-year lateral branches was only half of the resistance of the stem.Most clones can maintain the stability of each resistance and its proportion between years.The resistance was significantly negatively correlated with the growth rate as well as aboveground biomass,while the The correlation between resistance distribution and growth was not significant.(3)hydraulic efficiency was positively correlated with stomatal conductance and leaf water potential,and negatively correlated with instantaneous water use efficiency.There was no significant correlation between gas exchange parameters and aboveground biomass and growth rate.(4)clones have significant differences in the embolism vulnerability of the branch and the xylem anatomical structures.There were trade-offs between hydraulic efficiency and safety,and between hydraulic safety and aboveground biomass.Hydraulic efficiency,embolism vulnerability and growth are all positively correlated with vessel diameter and hydraulic diameter,and negatively correlated with mechanical strength of the vessels.The pit membranes of the high-yield clones were larger and thinner,with larger pores,smaller pit apertures,and shallower pit chambers.In summary,this study reveals the close relationship between hydraulic efficiency and growth.However,only hydraulic efficiency at the larger level(shoot,root,and whole-plant)can more reliably reflect the high-yield potential of poplars,which may be used as an indicator for rapid breeding of fast-growing and high-yield poplars varieties in the future.The hydraulic resistances of all organs were closely related to the growth,and the resistance distribution was not the main factor that determines growth.There was a coordination between hydraulic efficiency and stomatal conductance,which was mediated by leaf water potential.The diameter and mechanical strength of the vessels and the ultrastructure of the pits can determine the hydraulic properties of the xylem and the high-yield potential of the trees.It was also the basis for the trade-offs between hydraulic safety and efficiency as well as hydraulic safety and growth.