ASSESSING THE RELATIONSHIP BETWEEN WHOLE-PLANT HYDRAULIC CONDUCTANCE AND GROWTH PERFORMANCE AMONG LOBLOLLY PINE SAPLINGS

Climate change is increasing drought, and heavy winds globally, affecting forest resources. To improve tree tolerances to these changes researchers have initiated breeding economically important tree species like Pinus taeda. Physiological traits may be useful indicators of plant growth and stress tolerance. Hydraulic conductance (k) describes the relationship between water flow rate (F, kg s-1) and driving force (P, MPa) for a plant organ or whole-plant (kplant). Bent stems caused by winds can damage the xylem vessels to reduce the cross-sectional area available for k, and nucleate cavitation to reduce kplant. Tree growth rates have been linked to measures of hydraulic efficiency. Trees exposure to bending affects tree growth which could be mediated by kplant.However, it is unclear how it affects kplant. The hypotheses of the study were 1) kplant is a predictor of growth rates in trees and 2) stem bending affects kplant which in turns influences tree growth. This study assessed the relationship between kplant and growth rates among P. taeda saplings. A stem-bending experiment was performed on P. taeda saplings to assess the effect of bending on kplantand growth rates. During the 2023 growing season, kplant measurements were taken from the saplings (5 trees per genotype in each treatment) using a portable photosynthesis system and a pressure chamber. Growth metrics were recorded before and after experimentally manipulating stem bending exposure. Results showed that among individual trees of several loblolly pine genotypes, kplant had predictive power for pre-treatment height growth (R2 = 0.16, P = 0.02) and total volume growth rates (R2 = 0.11, P = 0.05). Stem bending treatments did not affect Δlog(kplant) (P = 0.63), post-treatment log(kplant) (P = 0.36); however, they affected Δdiameter growth (P > 0.001), post-treatment diameter growth rate (P > 0.001), Δvolume growth rate (P = 0.004) and post-treatment volume growth rates (P < 0.001). Genotypes affected Δheight growth rate (P = 0.006) only. These results suggest that kplant is a key determinant of growth, especially height in loblolly pine saplings. However, mechanical stress could impact tree growth through mechanisms other than water transport, as it may change growth patterns in response to stress.