Salt secretion and stomatal behaviour in Avicennia marina seedlings fumigated with the volatile fraction of light Arabian crude oil

Seedlings of the salt secreting mangrove A vicennia marina were exposed to fumes of the volatile fraction of light Arabian crude oil (VFCO) under controlled conditions. Rates of salt secretion were determined in leaves fumigated for 0, 3, and 6 h under four different salinity levels (10, 20, 30, and 40 ppt). Studying the effect of these fumigation periods on stomatal resistance and transpiration was restricted to one salinity level (20 ppt). Opposite to salinity, increasing the fumigation period significantly reduced both salt secretion and transpiration with a significant increase in the stornatal resistance to gas diffusion. During the first day of recovery from fumigation stress, different stomatal oscillation patterns were observed in the treated plants. The amplitude of the oscillations increased with the duration of fumigation, as did the time required for stomatal recovery. Seedlings fumigated for 3 h started to recover within 48 h, while full recovery in seedlings fumigated for 6 h required ahnost twice that period. The apparent recovery process was evident in the damping off of the amplitude of stornatal oscillations during the measurements period. Data presented herein show that (lie exposure of mangrove seedlings to VFCO disturbs the normal functions of two major structures in the leaves, i.e. the stomata and the salt glands, The ecophysiological significance of these results was discussed in relation to previous studies. (C) 2001 Elsevier Science Ltd. All rights reserved.