Effects of drought stress on photosynthetic gas exchange, chlorophyll fluorescence and stem diameter of soybean plants

Abstract

Changes in plant growth, photosynthetic gas exchange, chlorophyll fluorescence and stem diameter of soybean [Glycine max (L.) Merr.] plants under drought stress were studied. Total plant dry mass was reduced by 30 % compared to wellwatered control plants. Leaf water potential was slightly decreased by water stress. Water stress induced daytime shrinkage and reduced night-time expansion of stem. Photosynthetic rate, stomatal conductance and transpiration rate were significantly declined by water stress, while the intercellular CO 2 concentration was changed only slightly at the initiation of stress treatment. The maximum photochemical efficiency of photosystem 2 and apparent photosynthetic electron transport rate were not changed by water stress.Additional key words: Glycine max, growth, net photosynthetic rate, photochemical efficiency of photosystem 2, stomatal conductance, transpiration rate, water stress. ⎯⎯⎯⎯Soybean is one of the major and widespread crops in the world and is rather sensitive to water stress. Plants regulate their diurnal water status at a favourable level by the control of stomatal aperture (Farquhar and Sharkey 1982). Stomatal closure contributes to maintain high leaf water content and high leaf water potential, but it leads to a decrease in leaf photosynthesis. Stomatal closure reduces intercellar CO 2 concentration in leaves which imposes limitations CO 2 assimilation, and it causes an imbalance between photochemical activity at photosystem 2 (PS 2) and electron requirement for photosynthesis, and leads to increased susceptibility to photo-damage (He et al. 1995, Flagella et al. 1998. Several investigators have shown that the stem diameter of woody plants fluctuate diurnally (e.g., Imai et al. 1990 in grape, Simonneau et al. 1993 in peach, Ito et al. 1999 in pear). Simmoneau et al. (1993) used the micromorphometric techniques to observe rapid changes in the stem diameter in peach tree, which was closely related to the water status throughout the day. Water status of plants has been estimated directly by measuring the changes in stem diameter, however, the effect of water stress on growth in soybean plants has not been examined by this method.The present study was undertaken to evaluate the responses of photosynthesis to water stress in soybean plants, both in terms of CO 2 assimilation, as measured by leaf gas exchanges, and of the functionality of the photosynthetic apparatus, as assessed by chlorophyll fluorescence measurements. We also analysed the effect of water stress on stem diameter of intact soybean plants grown under drought.Seeds of soybean (Glycine max (L.) Merr.), latematuring cultivar New Tanbakuro were sown in mixture of granite regosol soil, Perlite and peat moss (2:1:1 (v/v/v)), and were irrigated daily. At 24 d after ⎯⎯⎯⎯ Abbreviations: c i -intercellular CO 2 concentration; DAT -days after the stress treatment; E -transpiration rate; ETR -apparent photosynthetic electron transport rate; F v /F m -variable to maximum chlorophyll fluorescence ratio (maximum photochemica...

Water restriction and physiological traits in soybean genotypes contrasting for nitrogen fixation drought tolerance

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Influence of foliar application of silicon on chlorophyll fluorescence, photosynthetic pigments, and growth in water-stressed wheat cultivars differing in drought tolerance

“…This might explain the increase in the value of F 0 /F m in Si-treated plants under water-deficit conditions (Figure 9). Several studies have reported stress-induced increases in the values of F 0 /F m and q N and decreases in F v /F m , q P , F 0 , and φPSII (Yordanov et al, 2000;Baker and Rosenqvist, 2004;Ohashi et al, 2006;Habibi and Hajiboland, 2013).…”

Effects of shade and drought stress on soybean hormones and yield of main-stem and branch

“…Unfavorable growing conditions such as excessive soil water and agricultural practices such as late planting, reduction in the ratio of red to far-red light (R : FR) and high plant density, reduce seed yield primarily by reducing branch growth and branch seed yield per plant (Green-Tracewicz et al, 2010). Water stress at the seedling and at the flowering stage decreases soybean yield by 20 and 46%, respectively (Shou et al, 1991) due to decreased photosynthetic rate, stomatal conductance and transpiration rate of soybean (Ohashi et al, 2006;Vu et al, 2001). Moreover, shade treatments have been shown to reduce yield and seed size (Tang et al, 2010) and also to reduce yield with no effect on seed size (Andrade and Ferreiro, 1996).…”