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

Rozema, J., Arp, W., van Diggelen, J., Kok, E. and Letschert,J. 1987. An ecophysiological comparison of measurements of thediurnal rhythm of the leaf elongation and changes of the leafthickness of salt-resistant Dicotyledonae and Monocotyledonae.—J.exp. Bot. 38: 442–453. The continuous measurement of leaf elongation and leaf thicknesswith the use of a rotation potentiometer set up revealed a rapidand sensitive reaction of halophytic plants to conditions affectingthe plant's water relations. At increased salinity (450 molm^–3 NaCl) the rate of leaf elongation decreased both inAster tripolium and in Sparlina anghca. Increased shrinkageduring the day and a long period for recovery swelling at nightin leaves of Aster iripolium at increased salinity illustratesthat water shortage is part of the cause of salinity-inducedgrowth reduction. All dicotyledonous species analysed (Aster tripolium, A triplexhastata, A. littoralis, Suaeda maritima and Beta vulgaris) showeda 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 rubrassp. litoralis, Elymus pycnanthus). With the exception of Triglochinmaritima none of the monocotyledonous halophytes tested (Sparlinaanglica, Juncus gerardii, J. maritimus, Festuca rubra ssp. litoralis,Elymus pycnanthus) exhibited a diurnal rhythm of leaf thicknesschanges, such as was observed for all dicotyledonous speciesstudied (Aster tripolium, Atriplex hastata, A. littoralis, Salicorniabrachyslachya, Suaeda maritima, Glaux maritima, Odontites vernassp. serotina). The diurnal pattern of the leaf elongation rateand the leaf thickness changes can be explained by variationof photosynthetic rate and transpiration water losses by stomatalclosure in the dark and opening in the light such as shown forthe dicotyledon species Glaux maritima. This difference betweendicot and monocot species in diurnal variation of the leaf elongationrate and leaf thickness may partly be explained in terms ofthe different position of the growth zone and possibly by adifference in elasticity of the tissue of halophytic monocotyledonsand dicotyledons. The consequences of these differences arediscussed. Key words: Leaf elongation rate, leaf thickness, water relations, salt resistance, Dicotyledonae, Monocotyledonae