Measuring water stress in Pinus patula Schiede ex Schlect. & Cham. seedlings

Abstract

A pot trial was conducted to investigate measures of water stress for Pinus patula seedlings planted for commercial forestry in South Africa. The objectives were to determine the efficacy of different equipment for quantifying water stress, and the effect of soil water availability at transplanting on seedling physiology. There were two dry soil treatments differing in terms of seedling root plug moisture at transplanting, dry (DD) and wet (WD), respectively, and three treatments consisting of well watered seedlings planted into wet soil (WWD, WWW and Control). Treatment WWD received no further water after planting while WWW was re-watered when seedlings were water stressed. The Control was maintained at field capacity for the trial period. Seedling physiology (shoot water potential, stomatal conductance and chlorophyll fluorescence) and soil temperature and water content were measured. Shoot water potential and stomatal conductance reflected plant physiological responses to changes in soil water content. Chlorophyll fluorescence measurements were variable and did not reflect treatment effects. A wet root plug at the time of transplanting increased seedling shoot water potential for three days in dry soil. Planting into wet soil increased shoot water potential for the duration of the trial. Soil water content affected soil temperature, with differences exceeding 5°C recorded on days with air temperatures over 30°C.