Acclimation potential of three evergreen tree species to wind-induced water stress in an urban green-roof environment

Abstract

We compared acclimation potential of three native, evergreen tree species to wind-exposure in an 6 urban green-roof environment. One year after planting on the green roof, Machilus thumbergii 7 retained all leaves and produced new leaves. In contrast, Fraxinus griffithii, and Quercus 8 myrsinifolia shed all leaves but produced more new leaves than the previous year. After two years, 9 current-year leaves of all three species had acclimated hydraulically (lower osmotic potentials at 10 saturation and turgor loss) to wind-induced water stress and leaf number increased to four to eight 11 times the initial amount. When trees were exposed to simulated winds in a greenhouse experiment, 12 osmotic adjustment was observed for current-year leaves of M. thumbergii, whereas leaves of F.13 griffithii and Q. myrsinifolia had hydraulic traits more vulnerable to wind-induced water stress 14 (higher osmotic potential and relative water content at turgor loss). We inferred that, M.15 thumbergii invests in hydraulic acclimation to retain current-year leaves in response to increased 16 wind, whereas F. griffithii and Q. myrsinifolia allocate resources to new leaf production. Our 17 results suggest both strategies achieve tree-level acclimation to wind exposure.