Aftereffects of Low and High Temperature Pretreatment on Leaf Resistance, Transpiration, and Leaf Temperature in Xanthium

Abstract

Leaf resistance for water vapor (total diffusion resistance minus boundary layer resistance), transpiration, and leaf temperature were measured in attached leaves of greenhouse-grown Xanthium strumarium L. plants that had been pretreated for 72 hours with high (40 C day, 35 C night), or low (10 C day, 5 C night) air temperatures. Measurements were made in a wind tunnel at light intensity of 1.15 cal cm-2 min-', air temperatures between 5 and 45 C, and wind speed of 65 cm sec1. Leaf resistances in low temperature pretreated plants were higher (8 to 27 sec cm-') than in controls or high temperature pretreated plants (0.5 to 8 sec cm-') at leaf temperatures between 5 and 25 C. Thus, the pretreatment influenced stomatal aperture.The temperature experienced by a plant during its immediate past history produces an effect on the net photosynthesis measured subsequently at any other temperature (3,5,6,(10)(11)(12)(13)(14). This aftereffect of temperature may be localized within the CO, assimilatory apparatus within the leaf (4). It may also be partially due to the stomata (5), since they govern the rate of supply of CO2 from the air to the carbon fixing tissues. Most studies of aftereffects of temperature upon photosynthesis have neglected this aspect.The stomata also regulate transpiration, and from simultaneous measurements of transpiration, leaf temperature, and water vapor pressure of the air, it is possible to calculate the total diffusion resistance to water vapor flux (Er). This resistance can be partitioned into the diffusion resistance across the boundary layer (ra) of air surrounding the leaf and the diffusion resistance of the leaf (r,) The area of uniform light produced by this lamp was approximately 40 cm in diameter when the irradiance was 0.80 cal cm2 min1. The irradiance used in this study was 1.0 to 1.3 cal cm-2 min-' net radiation of which 0.80 cal cm-2 min-' was from the lamp in the range 0.38 to 2.00 nm. The remaining portion was long wave radiation emitted by the Mylar ceiling and the floor of the wind tunnel. The intensity of the long wave portion of the net radiation increased as the air temperature in the wind tunnel increased. In all experiments, the average wind velocity at the leading edge of the leaf was kept constant at 63 cm sec-'. Experiments with blackened, copper-plated leaf models showed that this wind velocity corresponded to an average boundary layer resistance of 0.8 sec cm-' in leaves that were 10.0 to 11.0 cm across the downwind dimension. Humidity was either high or low. When high humidity was desired, water was allowed to flow through fiberglass filters in the air stream. A degree of control over the water vapor pressure in the air was obtained by regulating the temperature of the water supplied to the filters. Low humidity was attained by stopping the water flow across the filters and passing a portion of the air that was circulating in the wind tunnel through a dryer. As

Prechilling of Xanthium strumarium L. Reduces Net Photosynthesis and, Independently, Stomatal Conductance, While Sensitizing the Stomata to CO2

“…Figure 4 shows that at any intercellular CO2 concentration (except below 200 /A 1-' in leaves prechilled for 24 hr) stomatal conductance decreased with increasing duration of the chilling treatment. Drake and Salisbury (1) showed that stomata in prechilled leaves did not open as wide at any subsequent temperature between 5 and 45 C as did stomata in unchilled leaves. Tschape (14) observed that stomata responded sluggishly after chilling.…”

“…higher at the end of a 6-hr exposure to 25 C than 1 Stomatal Conductance in Relation to the Intercellular CO2 Concentration. In the control leaves, stomata hardly responded to changes in ambient and intercellular CO2 concentration.…”

“…The effect persists for at least 1 day after chilled plants are returned to a warmer environment (10). Prechilling also causes a reduction in stomatal aperture (1,14) but it is not clear whether this is due to a direct effect on the stomata (as proposed by Tschiipe [14]) or a response to an increased intercellular CO2 concentration, resulting from an impairment of the photosynthetic apparatus. It is also possible that reduced stomatal apertures in chilled plants are a response to a lowered water permeability of the roots and thus decreased water potential in the leaves.…”

Uso da água por plantas de arroz em competição com biótipos de Echinochloa crusgalli resistente e suscetível ao herbicida quinclorac

“…Assim, incrementos no metabolismo podem ser indiretamente aferidos em função da temperatura da folha. Normalmente essa diferença fica em torno de um ou dois graus, mas em casos extremos pode exceder a 5 o C (Drake & Salisbury, 1972;Atkin et al, 2000). A temperatura da folha das plantas de arroz não foi alterada em função do aumento na intensidade de competição com plantas de capim-arroz do biótipo resistente ao herbicida (Tabela 4).…”

Uso da água em biótipos de azevém (Lolium multiflorum) em condição de competição

“…Assim, incrementos no metabolismo podem ser indiretamente aferidos em função do gradiente entre temperatura da folha e do ar (T). Normalmente ess a diferença é de somente um ou dois graus, mas, em casos extremos, pode exceder 5 o C (Drake & Salisbury, 1972;Atkin et al, 2000). Uma vez que a  T não mostrou significância estatística, pode-se concluir que o metabolismo não foi seriamente afetado e que esse fator provavelmente possa ser excluído da participação na Gs.…”