Temperature and Transpiration Resistances of Xanthium Leaves as Affected by Air Temperature, Humidity, and Wind Speed
TL;DR: Leaf resistances decreased with increasing temperature, and silicone rubber replicas of leaf surfaces proved that the decrease was due to increased stomatal apertures, and transpiration varied less than would have been predicted on the basis of the water-vapor pressure difference between leaf and air.
Abstract: Transpiration and temperatures of single, attached leaves of Xanthium strumarium L. were measured in high intensity white light (1.2 calories per square centimeter per minute on a surface normal to the radiation), with abundant water supply, at wind speeds of 90, 225, and 450 centimeters per second, and during exposure to moist and dry air. Partitioning of absorbed radiation between transpiration and convection was determined, and transpiration resistances were computed.Leaf resistances decreased with increasing temperature (down to a minimum of 0.36 seconds per centimeter). Silicone rubber replicas of leaf surfaces proved that the decrease was due to increased stomatal apertures. At constant air temperature, leaf resistances were higher in dry than in moist air with the result that transpiration varied less than would have been predicted on the basis of the water-vapor pressure difference between leaf and air.The dependence of stomatal conductance on temperature and moisture content of the air caused the following effects. At air temperatures below 35 C, average leaf temperatures were above air temperature by an amount dependent on wind velocity; increasing wind diminished transpiration. At air temperatures above 35 C, leaf temperatures were below air temperatures, and increasing wind markedly increased transpiration. Leaf temperatures equaled air temperature near 35 C at all wind speeds and in moist as well as in dry air.
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TL;DR: A comparison of plants from contrasting thermol regimes in Thermally Contrasting Climates and adoptive responses in the heat stability 0/ the photosynthetic apparatus highlights the need to understand more fully the role of photosynthesis in climate change.
Abstract: INTRODUCTION 492 ECOLOGICAL ASPECTS OF PHOTOSYNTHETIC TEMPERATURE ADAPTATION 493 Photosynthetic Temperature Dependence in Thermally Contrasting Climates ........ 493 Photosynthetic Temperature Acclimation 497 Seasonal acclimation in natural habitats ...... ....... 497 Studies in controlled environments 499 THE MECHANISTIC BASIS FOR PHOTOSYNTHETIC RESPONSE AND ADAPTATION TO TEMPERATURE 504 Reversible Temperature Respon.ses 505 Stomata! effec� o� the . temJH!.rature response 0/ photo.rynthesis ......... ....... 505 Interacttons with /lght mtenslty 507 C, photo.rynthesis (lM photorespiration 507 C, photo.rynthesis 515 Comparison 0/ plants from contrasting thermol regimes ...... ...... 517 ["eversible Temperature Respon.ses 519 Low temperature sensitMty ....... 519 High temperature sensitivity 524 Adoptive responses in the heat stability 0/ the photosynthetic apparatus 530 CONCLUDING REMARKS 532
2,779 citations
01 Jun 1997
TL;DR: The primary effect of plants response of plants to rising atmospheric CO2 (Ca) is to increase resource use efficiency, and at the same time it stimulates higher rates of photosynthesis and increases light-use efficiency as discussed by the authors.
Abstract: ▪ Abstract The primary effect of the response of plants to rising atmospheric CO2 (Ca) is to increase resource use efficiency. Elevated Ca reduces stomatal conductance and transpiration and improves water use efficiency, and at the same time it stimulates higher rates of photosynthesis and increases light-use efficiency. Acclimation of photosynthesis during long-term exposure to elevated Ca reduces key enzymes of the photosynthetic carbon reduction cycle, and this increases nutrient use efficiency. Improved soil–water balance, increased carbon uptake in the shade, greater carbon to nitrogen ratio, and reduced nutrient quality for insect and animal grazers are all possibilities that have been observed in field studies of the effects of elevated Ca. These effects have major consequences for agriculture and native ecosystems in a world of rising atmospheric Ca and climate change.
1,906 citations
01 Jan 1982
TL;DR: The stomatal aperture appears to be controlled by complex mechanisms which operate to maintain a variable balance between allowing CO2 uptake to proceed, while restricting the loss of water vapor, and preventing leaf desiccation as mentioned in this paper.
Abstract: Stomatal apertures are the major pathway for the movement of CO2 from the atmosphere into the mesophyll of leaves. The presence of this pathway for the movement of gases also results in water loss from the hydrated surfaces within leaves to the atmosphere. Stomatal aperture appears to be controlled by complex mechanisms which operate to maintain a variable balance between allowing CO2 uptake to proceed, while restricting the loss of water vapor, and preventing leaf desiccation. Recent reviews have examined the physiological bases of stomatal function (Raschke 1979; Allaway and Milthorpe 1976) and stomatal responses to environment (Sheriff 1979; Burrows and Milthorpe 1976; Hall et al. 1976). Analyses which integrated stomatal effects on CO2 exchange, transpiration, and energy balance were developed based upon theory (Cowan 1977), which have led to hypotheses concerning optimal stomatal function (see Chap. 17, this Vol.; Cowan and Farquhar 1977). However, information concerning the simultaneous responses of stomata, water loss, and CO2 assimilation rates has not been reviewed for plants in natural environments.
625 citations
TL;DR: The capacity for isoprene emission evolved many times in plants, probably as a mechanism for coping with heat flecks, and is an example of isoprenoids enhancing membrane function, although the mechanism is likely to be different from that of sterols.
581 citations
Cites result from "Temperature and Transpiration Resis..."
...1) that is similar to one reported by Drake et al. (1970)....
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...This system is similar to one used by Drake et al. (1970) but different from the suggestion of Ehleringer (1991) who recommended that the thermocouples be inserted into the part of the leaf to be measured....
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TL;DR: The evolutionary context of leaf shape diversification is reviewed, the proximal mechanisms that generate the diversity in extant systems are discussed, and the evidence for each the above hypotheses is considered in the context of the functional significance of Leaf shape.
Abstract: Angiosperm leaves manifest a remarkable diversity of shapes that range from developmental sequences within a shoot and within crown response to microenvironment to variation among species within and between communities and among orders or families. It is generally assumed that because photosynthetic leaves are critical to plant growth and survival, variation in their shape reflects natural selection operating on function. Several non-mutually exclusive theories have been proposed to explain leaf shape diversity. These include: thermoregulation of leaves especially in arid and hot environments, hydraulic constraints, patterns of leaf expansion in deciduous species, biomechanical constraints, adaptations to avoid herbivory, adaptations to optimise light interception and even that leaf shape variation is a response to selection on flower form. However, the relative importance, or likelihood, of each of these factors is unclear. Here we review the evolutionary context of leaf shape diversification, discuss the proximal mechanisms that generate the diversity in extant systems, and consider the evidence for each the above hypotheses in the context of the functional significance of leaf shape. The synthesis of these broad ranging areas helps to identify points of conceptual convergence for ongoing discussion and integrated directions for future research.
393 citations
Cites background from "Temperature and Transpiration Resis..."
...Actual leaf temperature measurements show that large leaves can operate at below-ambient temperatures even on hot days, as a result of high rates of latent heat loss through transpiration (Drake et al. 1970; Gates 1980; Hegazy and El Amry 1998)....
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TL;DR: The following method consists essentially of taking a primary impression of the surface with a silicone rubber plastic and using this to form secondary transparent replicas to be used for microscopic study of surfaces.
Abstract: THE use of transparent replicas is a convenient method for the microscopic study of surfaces. Perfectly dry structures can be replicated with plastic substances such as ‘Collodion’, ‘Formvar’ or methacrylate, but a serious disadvantage to the general use of these materials is that they ‘mist’ when allowed to harden in a moist atmosphere. Accordingly, they cannot be used satisfactorily with specimens that either become distorted when dry or, like many biological specimens, have a naturally wet surface. The following method, which overcomes this difficulty, consists essentially of taking a primary impression of the surface with a silicone rubber plastic and using this to form secondary transparent replicas.
177 citations
TL;DR: Stomata of Zea mays L. respond to changes in hydrostatic pressure in the water supply of the leaves almost instantaneously and in all leaf parts simultaneously, therefore, the leaf is a hydraulic unit and their aperture is controlled by the water potential in theWater-conducting system.
Abstract: Stomata of Zea mays L respond to changes in hydrostatic pressure in the water supply of the leaves almost instantaneously and in all leaf parts simultaneously Therefore, the leaf is a hydraulic unit The stomata are part of it and their aperture is controlled by the water potential in the water-conducting system Stomatal aperture is not uniquely related to the relative water content of a leaf The relation depends also on the humidity in the air and is different for the upper and the lower epidermis
160 citations