Abstract

Rozema, J., Arp, W., van Diggelen, J., Kok, E. and Letschert, J. 1987. An ecophysiological comparison of measurements of the diurnal rhythm of the leaf elongation and changes of the leaf thickness of salt-resistant Dicotyledonae and Monocotyledonae.—J. exp. Bot. 38: 442–453.

The continuous measurement of leaf elongation and leaf thickness with the use of a rotation potentiometer set up revealed a rapid and sensitive reaction of halophytic plants to conditions affecting the plant's water relations. At increased salinity (450 mol m–3 NaCl) the rate of leaf elongation decreased both in Aster tripolium and in Sparlina anghca. Increased shrinkage during the day and a long period for recovery swelling at night in leaves of Aster iripolium at increased salinity illustrates that water shortage is part of the cause of salinity-induced growth reduction.

All dicotyledonous species analysed (Aster tripolium, A triplex hastata, A. littoralis, Suaeda maritima and Beta vulgaris) showed a day/night ratio of the leaf elongation rate lower than 1, while this ratio was higher than or equal to 1 in Monocotyledons (Spartina anglica, Juncus gerardii, J. maritimus, Festuca rubra ssp. litoralis, Elymus pycnanthus). With the exception of Triglochin maritima none of the monocotyledonous halophytes tested (Sparlina anglica, Juncus gerardii, J. maritimus, Festuca rubra ssp. litoralis, Elymus pycnanthus) exhibited a diurnal rhythm of leaf thickness changes, such as was observed for all dicotyledonous species studied (Aster tripolium, Atriplex hastata, A. littoralis, Salicornia brachyslachya, Suaeda maritima, Glaux maritima, Odontites verna ssp. serotina). The diurnal pattern of the leaf elongation rate and the leaf thickness changes can be explained by variation of photosynthetic rate and transpiration water losses by stomatal closure in the dark and opening in the light such as shown for the dicotyledon species Glaux maritima. This difference between dicot and monocot species in diurnal variation of the leaf elongation rate and leaf thickness may partly be explained in terms of the different position of the growth zone and possibly by a difference in elasticity of the tissue of halophytic monocotyledons and dicotyledons. The consequences of these differences are discussed.

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