Early responses of Bassia diffusa (Thunb.) Kuntze to submergence for different salinity treatments

Early responses of the salt marsh succulent Bassia diffusa (Thunb.) Kuntze to combined salinity and submergence were studied in a laboratory experiment aimed at determining the pattern of the response of photosynthetic pigments, membrane stability, oxalic acid and water relations to these stressors. Three key stages in the response were identified. A drop in chlorophyll a + b within 6 h (4.2 +/- 0.2 to 2.4 +/- 0.3 mg g(-1) DM) with a corresponding increase in carotenoid concentration (0.6 +/- 0.1 mg g(-1) DM) indicated an immediate response to submergence. Oxalic acid concentration was highest on Day 4(1.7 g g(-1) DM) as opposed to control levels, indicative of its role in submergence tolerance, thus Day 4 may be the peak of positive acclimation. The third phase was marked by a sharp increase in electrolyte leakage to 47.5 +/- 2.6% on Day 10, from 9.4 +/- 1.4% on Day 7, with a corresponding decrease in total dissolved solutes between Days 7 and 10. Results suggest that oxalic acid accumulates under submergence possibly as a stabilising osmolyte. The threshold for tolerance of the species under submergence is 7 days with membrane damage thereafter. B. diffusa would not survive prolonged submergence (>7 days) but could survive submergence of short duration (<7 days) through continuous underwater photosynthesis, accumulation of osmolytes such as oxalic acid and carotenoid, and maintenance of relative water content and succulence within control levels. These data show that this upper intertidal salt marsh plant would be sensitive to prolonged inundation as a result of sea level rise or due to estuary mouth closure and a subsequent rise in water level. (c) 2012 SAAB. Published by Elsevier B.V. All rights reserved.