trees are an important source of wild germplasm for sustainable forestry. wild pear germplasm (pyrus boisseriana) was collected from a forest ecosystem and resistance potential to drought stress was surveyed in a greenhouse. in six-month seedlings, signs of leaf rolling appeared after 18 days without water (drought simulation). gas exchange parameters, such as net photosynthesis, stomatal condu...

The transfer of water from phloem into xylem is thought to mitigate increasing hydraulic tension in the vascular system of trees during the diel cycle of transpiration. Although a putative plant function, to date there is no direct evidence of such water transfer or the contributing pathways. Here, we trace the radial flow of water from the phloem into the xylem and investigate its diel variati...

The water relations of pepper plants (Capsicum frutescens L.) under conditions conducive to guttation were studied to evaluate the control of plant water stress with polyethylene glycols. The addition of polyethylene glycol 6000 to the nutrient solution resulted in water relations similar to those expected in soil at the same water potentials. Specifically, xylem pressure potential in the root ...

Young barley (Hordeum vulgare L. cv Arivat) leaves were examined anatomically and physiologically to infer the pathway of transpirational water movement and to explain why the growing region is more responsive to osmotic stress than the expanded blade. Vessels with open lumens extend from the intercalary meristem to the expanded blade, and all vessels are clustered in five vascular bundles that...

Xylem cavitation and its recovery were studied in 1-year-old stems of ring-porous Quercus serrata Thunb. and diffuse-porous Betula platyphylla var. japonica Hara. The Q. serrata had 5-100 microm vessel diameter in the functional current xylem and 5-75 microm in nonconducting 1-year-old xylem; B. platyphylla had a narrower range of vessel diameters of 5-55 microm and more than double the number ...

A comprehensive model of stem and root diameter variation was developed. The stem (or root) was represented using two coaxial cylinders corresponding with the mature xylem and the extensible tissues. The extensible tissues were assumed to behave as a single cell separated from the mature xylem by a virtual membrane. The mature xylem and the extensible tissues are able to dilate with temperature...

Direct determinations and indirect calculations of phloem turgor pressure were compared in white ash (Fraxinus americana L.). Direct measurements of trunk phloem turgor were made using a modified Hammel-type phloem needle connected to a pressure transducer. Turgor at the site of the direct measurements was calculated from the osmotic potential of the phloem sap and from the water potential of t...

This study examined the linkage between xylem vulnerability, stomatal response to leaf water potential ( Y L ), and loss of leaf turgor in eight species of seasonally dry tropical forest trees. In order to maximize the potential variation in these traits species that exhibit a range of leaf habits and phenologies were selected. It was found that in all species stomatal conductance was responsiv...

We investigated hydraulic constraints on water uptake by velvet mesquite (Prosopis velutina Woot.) at a site with sandy-loam soil and at a site with loamy-clay soil in southeastern Arizona, USA. We predicted that trees on sandy-loam soil have less negative xylem and soil water potentials during drought and a lower resistance to xylem cavitation, and reach E(crit) (the maximum steady-state trans...