Leaf Photosynthesis and Conductance of Selected Triticum Species at Different Water Potentials

Abstract

Leaf ps exchange characteristics ofa desert annual (Triticum kotschyi [Boiss.j Bowden) appears to maintain a higher degree of relative stomatal opening at reduced water potentials than T. aestivum, it is not clear if this is the only factor involved in the control of photosynthesis (13). In this study, we report that stomata had an important role in causing the relatively high photosynthetic rates of T. kotschyi under well watered conditions, but under water deficits the mesophyll capacity for photosynthesis was more important. Unvernalized plants were grown in growth chambers at 2O°C, 60% RH, and 14 h light (600 Mmol m-2 s-' PAR at pot level). Three seeds were planted per pot about 1.5 cm deep in pots holding 1 L of sterilized sand. Emerged seedlings were thinned to 1 per pot after a week and the remaining plants watered daily with 25% Hoagland solution until the stress treatments were imposed. In the first experiment plants of T. kotschyi and T. aestivum were grown under well watered conditions for 42 d after which gas exchange measurements were made as described below. The experiment was randomized in complete blocks with five replications. In a second experiment plants ofthe two species were grown for 35 d under well-watered conditions before water deficits were imposed by withholding water from pots. The experiment was randomized in complete blocks with four replications with genotype and water stress level (days without water) as experimental factors. Gas exchange measurement for the four water levels were made over a 5-d period with a given stress level completed each day. Plants of each species were measured at 0, 2,3, and 4 d after withholding water from pots. The measurement order for stress level and species within a stress level was randomized. In a third experiment water deficits were applied to T. kotschyi and T. aestivum over a more prolonged period. The water-holding capacity of the sand was determined and the weight of each pot, filled with equal volumes of dry sand, was recorded. The pots were weighed daily and their percent water calculated. Plants were watered to the maximum water holding capacity each day before the start of the stress treatment. For the stress treatment, plants were grown under well watered conditions for 24 d and then allowed to dehydrate to just below 20% of pot water-holding capacity, which took 4 d, and then were watered each day thereafter up to 20% of pot water-holding capacity for a 10-day period. Thus, the stress treatment consisted of a 4-d dehydration period followed by 10 d of prolonged stress. Pots from well watered treatments were watered daily to their pot water holding capacity. The experiment was completely randomized with three replications. MATERIALS AND METHODSGas Exchange Measurements.

Promotive effects of phosphorus on crop productivity, enzyme activities, anthraquinone and sennoside content inCassia toraL. – a medicinal herb

“…The P 3 concentration proved optimum and produced maximum values for these attributes studied (Figures 2, 3 and 4). A higher transpiration rate recorded in phosphorus treated leaves of the plant could be expected as transpiration is known to depend on stomatal conductance (Johnson et al 1987;McMurtrie 1993). Since the stomatal conductance showed improvement in the phosphorus supplied plants, a significant increase in the rate of transpiration is obviously expected.…”

Fluorescence Quenching and Gas Exchange in a Water Stressed C3 Plant, Digitalis lanata

“…1) are typcial for a long-term water stressed, but attached and recoverable leaf of a C3 species (14,17,29). Similar curves were obtained with D. lanata plants at different light intensities (Fig.…”

“…The fact that the intercellular CO2 concentration (C*)' does not decrease to the CO2 compensation point, but remains high even during moderate stress in several species (14,17, 29), invalidates the hypothesis that only stomatal closure is responsible for the loss of net photosynthesis via CO2 depletion (13).…”

Influence of Water Stress Conditioning on Photosynthetic Water Stress Response of Switchgrass (Panicum Virgatum L.) and Tall Fescue (Festuca Arundinacea Schreb.)

“…They observed a linear decrease in photosynthesis when the leaf water potential declined to less than -1.1 MPa. Johnson et al (1987) investigated the photosynthesis response of Triticum species and found a curvilinear relationship between water potential and photosynthesis. Based on these observations it was concluded that the data showed the linear part of a curvilinear relationship, so the intercept data were not used as the maximum value of photosynthesis.…”

“…Ghashghaie and Saugier (1989) provided valuable information about the photosynthesis and stomatal movement of tall fescue subjected to drought and different nitrogen levels at the same time. Johnson et al (1987) observed the photosynthesis and conductance of Triticum species over a soil drying cycle. Jones et al (1980) described the stomatal behaviour and morphological changes of perennial ryegrass subjected to slow and rapid rates of water stress.…”