Monitoring the Short-Term Response to Salt Exposure of Two Genetically Distinct <i>Phragmites australis</i> Clones with Different Salinity Tolerance Levels

Abstract

Aims: Two genetically distinct clones of Phragmites australis were used to investigate the im mediate response induced by osmotic stress. The study aimed at elucidating if the response time, the inhibition rate and the recovery from salinity stress vary between these two genotypes. The experimental work was conducted at the laboratory of the Institute of Bioscience, Aarhus Univer sity, Denmark. Methods: The light-saturated photosynthetic rate ( P max ), stomata conductance ( g s ) and transpiration rate ( E ) were measured over different periods of salt exposure (15, 70 and 240 minutes) and at different salt concentrations (20 and 40 parts per thousand salinity). Important findings: The osmotic stress induced stomata closure and reduction of P max and E for both clones. The clone-specific responses as measured through physiological parameters were negatively cor related with exposure time and salt concentration. During the 4-hour exposure at 20 ppt, the two clones were inhibited at different rates. The salt-sensitive Land-type showed an immediate reduc tion of P max , g s and E . No recovery was observed after removing the salt solution. At the same salt concentration, the reduction of P max g s and E of the Greeny-type was lower and immediate recov ery was observed when the root zone was rinsed. Both clones were irreversibly inhibited after 4 hours of exposure to 40 ppt. Recovery was primarily related to exposure time, as P max , g s and E rates of both clones recovered completely after fresh-water rinsing in the 15-minute experiment. The Greeny-type also recovered after the 70-minute exposure, but not the Land-type. We<