© 2003 Heron Publishing—Victoria, Canada
Variation in drought response of sal (Shorea robusta) seedlings
Satish C. Garkoti (1, 4), Donald B. Zobel (2, 3) and Surendra P. Singh (1)
1. Department of Botany, Kumaun University, Naini Tal 263 002, India / 2. Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA / 3. Author to whom correspondence should be addressed (zobeld@bcc.orst.edu) / 4. Department of Ecology, Assam University, Silchar 788 011, Assam, India / Received August 23, 2002; accepted April 18, 2003; published online September 15, 2003
Summary
Plant development and distribution in areas with seasonal rainfall are often related to the ability of plants to postpone
desiccation or tolerate low water potentials during drought. Regeneration of Shorea robusta Gaertn. (sal), a commercially valuable, widely distributed tree of the Indian tropical belt, is unsuccessful at the base
of the Himalaya. Seedling shoots die back repeatedly during the long drought that follows the monsoon rain. During the course
of one year, we monitored changes in plant and soil water potentials (Ψ), leaf conductance (gw), osmotic and elastic adjustment, and xylem conductance of sal seedlings of different sizes from three landforms: an alluvial
plain at 540 m elevation, a slope at 510 m, and a montane site at 1370 m. Predawn plant Ψ and gw were lowest in the smallest seedlings (< 20 cm tall). Across sites and seasons, seedlings > 100 cm tall had higher morning
gw than seedlings in the other size classes. In all size classes, plant Ψ was lowest during early summer, when leafing begins.
Among sites, Ψ and gw were lowest in seedlings at the montane site. Osmotic potential was lowest during leaf development and highest during the
rainy season, and tissue elasticity was highest during winter. As leaf area increased during leaf development, xylem conductance
per unit of xylem cross-sectional area also increased. We conclude that low Ψ is unlikely to be a major cause of seedling
mortality. Small seedlings, with low Ψ, had low leaf conductance. Adjustments of osmotic and elastic properties appear to
aid responses of seedlings to drought.
Keywords:
forest regeneration, Himalaya, India, leaf conductance, osmotic potential, seedling size, tissue elasticity, water potential,
xylem conductance.
