Changes in Water Relations, Water Flux, and Root Exudate Abscisic Acid Content With Cold Acclimation of Pinus sylvestris L

Abstract

Scotch pine seedlings (Pinus sylvestris L.) were subjected to 6 week photoperiod and thermoperiod treatments to induce different levels of cold acclimation. The water content, relative water content, xylem pressure potential, transpiration rate, root hydraulic conductance, and abscisic acid (ABA) content of root exudate were then measured.

Water content decreased in woody stems and needles with cold acclimation but not in the roots and green stems. There was a close correlation between relative water content and water content of woody stems and needles as well as a decrease in xylem pressure potentials of hardy needles, indicating that the reduction in water content was at least partially due to increased water deficit. The increased water deficit was not caused by increased water loss since transpiration rates decreased in hardy shoots. Water uptake was reduced by decreased root hydraulic conductance which could account for the shoot water deficits. Root hydraulic conductance and transpiration rate returned to non-acclimated levels after warm temperature exposure. ABA levels were highest in the root exudate collected in the morning from non-acclimated plants.