Physiological and Morphological Responses of Three Half-Sib Families of Loblolly Pine to Water-Stress Conditioning

Abstract

The effect of water-stress conditioning on drought tolerance of three open-pollinated families of loblolly pine (Pinus taeda L.) during water stress was investigated. Seedlings were subjected to one of two levels of prolonged, sublethal drought or were kept well watered. After the conditioning period, photosynthesis, transpiration, and growth were evaluated. Photosynthesis was decreased greatly with reduced needle water potential. Conditioned seedlings generally maintained positive net photosynthesis to water potentials 0.15 (moderate water-stress conditioning) and 0.40 (severe water-stress conditioning) MPa lower than those of control seedlings. This response was likely the result of an acclimation of the photosynthetic process resulting in less nonstomatal inhibition of photosynthesis at low needle water potentials. Under well-watered conditions, transpiration, but not photosynthesis, was reduced greatly by the conditioning treatments and resulted in improved water-use efficiency. Root growth was affected more by water stress than shoot growth, causing a decrease in root/shoot ratio. Genetic differences in photosynthetic acclimation were not apparent. However, compared to seedlings representing two Virginia seed sources, a family from Texas, known for its superior drought tolerance, had the lowest root/shoot ratio and the least change in transpiration in response to water-stress conditioning. For. Sci. 34(2):487-495.

Pinus taeda, photosynthesis, transpiration drought tolerance, acclimation