Experimental Evidence of the Impacts of Different Root-Pruning Intensities on Post-Transplant Water Potential and Xylem Hydraulic Conductivity in Two Tree Species

Abstract To improve transplanting techniques, it is necessary to understand root-pruning induced declines in xylem water transport and post-transplant environmental effects. In this study, we evaluated the relationship between water potential and hydraulic conductivity ( K s ) in saplings of Larix kaempferi and Betula maximowicziana , whose roots were pruned in order to improve our understanding of the transplanting technique. Root-pruning treatments were applied to saplings of both species based on their basal root diameters. After transplanting, the water potential and K s were measured. In addition, the vulnerability curve was obtained using a centrifuge method by quantifying the relationship between decreasing xylem pressure and the percentage loss of K s , allowing a comparison of water stress tolerance between the two species. Betula maximowicziana had higher K s and was more vulnerable to water stress induced embolism than L. kaempferi . In L. kaempferi , no decrease in K s was observed regardless of the level of root pruning, and all saplings survived after transplanting. In B. maximowicziana , saplings subjected to root pruning exhibited a decline in the water potential during midsummer, along with a reduction in K s . Moreover, the number of dead saplings increased with increasing levels of root pruning. For the two species, a relationship was found between increasing level of root pruning and post-transplant mortality in the more water stress vulnerable species, B. maximowicziana . The relationships among post-transplant changes in water potential, reductions in K s associated with root pruning, and sapling survival provide a useful framework for selecting transplanting methods and improving transplant success rates.