Impact of long-term drought on xylem embolism and growth in Pinus halepensis Mill.

Abstract

The present study was carried out to elucidate the response mechanisms of 50-year-old Pinus halepensis Mill. trees to a long-term and severe drought. The amount of water available to trees was artificially restricted for 12 months by covering the soil with a plastic roof. Over the short term a direct and rapid impact of drought was evident on the water relations and gas exchanges of trees: as the soil dried out in the Spring, there was a concurrent decrease of predawn water potential; transpiration was strongly reduced by stomatal closure. Seasonal changes in the water volume fractions of twig and stem xylem were observed and interpreted as the result of cavitation and refilling in the xylem. When droughted trees recovered to a more favourable water status, refilling of embolized xylem was observed; twig predawn water potentials were still negative in the period when the embolism was reversed in the twig xylem. A few months after the removal of the covering, no differences in whole plant hydraulic resistance were observed between droughted and control trees. Needle and shoot elongation and stem radial growth were considerably reduced in droughted trees; no strategy of trees to allocate carbon preferentially to the stem conducting tissues was apparent throughout the experiment. An after-effect of the drought on growth was observed

Climatic significance of tree-ring width and intra-annual density fluctuations in Pinus pinea from a dry Mediterranean area in Portugal

“…This finding confirms the studies of Villalba and Veblen [57], Masiokas and Villalba [40] and Bouriaud et al [5]. Moreover, P. pinea shows a high capacity to store water [42], which could minimize episodic water stress events during the early growing season [4,39]. .…”

Temperate forest trees and stands under severe drought: a review of ecophysiological responses, adaptation processes and long-term consequences

“…As a result of sharp increases in soil water potential during drought progression, both absorption and transfer of water are disrupted so that maintaining a hydraulic continuum within the tree is a real challenge: (1) there is an exponential increase of in soil and soil-to-root resistance to water as soil dries, limiting water uptake; (2) the occurrence of cavitation inside the xylem increases as leaf water potential decreases, limiting or even stopping water transfer. As shown previously, one of the possible induced consequences is the reduction of leaf area, which in turn reduces carbon fixation after soil re-watering, and then inducing growth reduction [17].…”

Diurnal dynamics of water transport, storage and hydraulic conductivity in pine trees under seasonal drought

“…Additionally, some of the measurements involving the cutting of xylem under tension might have overestimated the levels of embolism and recovery (Wheeler et al 2013) and hence must be taken with caution. In P. halepensis under drought, embolism repair was detected using acoustic emissions, a nonquantitative method (Borghetti et al 1991(Borghetti et al , 1998. We hypothesize that water storage and maintenance of hydraulic conductivity must be integral components of the water management in P. halepensis to sustain activity and survival under continuous dry conditions of the summer.…”