Seasonal and daily cycles of stem radial variation of Pinus pinaster in a drought-prone environment

摘要

High resolution measurements of stem diameter variation can provide valuable information on thegrowth process as well as the tree water status. This study investigates the hourly variations in stemradial increment of maritime pine growing on the west coast of Portugal, under a Mediterranean climatewith a pronounced summer drought. We tested the hypotheses that (1) stem radius variation in maritimepine has a daily and seasonal pattern that reflects the availability of water and (2) that once the internalwater storage is depleted the tree enters a quiescent state. During 2010, stem radius variations were monitoredin four similar trees with automatic dendrometers. Tree water deficit was extracted from the stemradial variation. The stem cycle approach was used to divide the daily cycles into contraction, recoveryand increment phases. The seasonal cycle was divided into five periods: winter dormancy, spring growth,pre-summer contraction, summer quiescence and autumn re-hydration. Amplitude and duration of eachphase were calculated for each cycle and correlated with precipitation, maximum and minimum temperature.Continuous positive radial increment started in spring and reached its maximum by the endof June. A shrinking period was observed in summer, with amplitudes of contraction and recovery 10times higher than in the other periods. The inability of the trees to recover from the water lost due totranspiration was responsible for stem shrinking and quiescence observed during summer. In autumn,a period of re-hydration and rapid expansion was observed after precipitation, restoring the tree to aphysiologically active state. Daily variations in stem radius of maritime pine were mainly determined bythe course of transpiration and thus dependent on temperature and tree water status.