Root temperature drives winter acclimation of shoot water relations in Cryptomeria japonica seedlings

Abstract

In many temperate evergreen plant species, reductions in turgor loss point of leaves (Ψtlp) and leaf osmotic potential at full turgor (πsat) occur from late summer to winter. To test the hypothesis that this seasonal change in leaf water relations is driven by root temperature, we manipulated the temperature of the roots and shoots of Cryptomeria japonica D. Don seedlings separately. Whole-plant warming diminished the seasonal changes in shoot water relations observed in the control plants, whereas shoot warming did not. Compared with the controls, root warming diminished the change in Ψtlp but not in πsat, whereas cooling accelerated the seasonal changes in shoot water relations. These results indicate that: (1) temperature responses of roots are involved in the seasonal changes in Ψtlp from late summer to winter; and (2) root temperature is partly responsible for the simultaneous changes in πsat. Wholeplant cooling caused increased root hydraulic resistance, suggesting that seasonal changes in shoot water relations represent adaptive responses to increased root hydraulic resistance at low root temperatures. © 2005 Heron Publishing.