Water stress of four windbreak tree species during soil drying

ABSTRACT:

Water relations for green ash, hackberry. American elm, and Siberian elm, trees used in windbreak plantings in the Northern Great Plains, were evaluated to determine response to increasing soil water deficits and to relate results to field observations on competition among trees and adjacent crops and to tree growth characteristics. Leaf water potentials of green ash and hackberry, in comparison with American and Siberian elm, declined at different rates during a 2-year field study. From the initial sample date (full leaf expansion) to the final sample date (leaves senescencing), leaf water potential dropped 30.1 bars for green ash and 27.9 bars for hackberry. These reductions compared with 10.1- and 6.2-bar-reductions for American and Siberian elm, respectively. In a controlled-environment chamber, transpiration rates at high soil water potentials (low water stress) were considerably higher for Siberian elm than for green ash and American elm. The higher water stress in leaves of green ash and hackberry contributes to early growth cessation and leaf drop during late summer, which should reduce total soil water use by the trees and leave more water for adjacent crops. If Siberian elm were selected for early leaf drop, it probably would initiate hardening processes earlier and have greater tolerance to winter injury and stress-related disease and insect attack.