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Decreased Stomatal Conductance (decreased + stomatal_conductance)
Selected AbstractsDisentangling effects of an experimentally imposed extreme temperature event and naturally associated desiccation on Arctic tundraFUNCTIONAL ECOLOGY, Issue 6 2006F. L. MARCHAND Summary 1Climate projections suggest that extreme events will increase in frequency during this century. As tundra is recognized to be among the most vulnerable biomes, we exposed patches of arctic tundra vegetation to an experimental heatwave (by infrared irradiation), followed by a recovery period. The heating increased the surface temperature with an average of 7·6 °C during 13 days, which slightly exceeded the longest climatic episode with such a temperature deviation since 1961. 2The heatwave decreased stomatal conductance (gs) and PSII maximum efficiency (Fv/Fm), although there were differences in response among the four target species. Salix arctica Pall. (shrub) was affected during the heatwave and could not recover. In Carex bigelowii Tor. ex Schwein (sedge) and Pyrola grandiflora Radius (forb), on the other hand, the effects on gs and Fv/Fm became clear, particularly in the aftermath of the heatwave, whereas Polygonum viviparum L. (forb) was never stressed. 3Effects of the heat on gs were mainly indirect, through increased desiccation, whereas effects on Fv/Fm were more related to leaf temperature (although not in all species). The observed changes can therefore probably be ascribed to a combination of heat and drought causing dysfunctions that ultimately led to senescence. 4Two conclusions of this study, species-specific responses and increased leaf mortality, indicate that more frequent extreme temperature events accompanied by desiccation might alter/endanger tundra communities in a future climate. Predictions of global change effects on arctic ecosystems should therefore take into account the impact of extremes. [source] Photosynthetic responses of Mojave Desert shrubs to free air CO2 enrichment are greatest during wet yearsGLOBAL CHANGE BIOLOGY, Issue 2 2003Elke Naumburg Abstract It has been suggested that desert vegetation will show the strongest response to rising atmospheric carbon dioxide due to strong water limitations in these systems that may be ameliorated by both photosynthetic enhancements and reductions in stomatal conductance. Here, we report the long-term effect of 55 Pa atmospheric CO2 on photosynthesis and stomatal conductance for three Mojave Desert shrubs of differing leaf phenology (Ambrosia dumosa,drought-deciduous, Krameria erecta,winter-deciduous, Larrea tridentata,evergreen). The shrubs were growing in an undisturbed ecosystem fumigated using FACE technology and were measured over a four-year period that included both above and below-average precipitation. Daily integrated photosynthesis (Aday) was significantly enhanced by elevated CO2 for all three species, although Krameria erecta showed the greatest enhancements (63% vs. 32% for the other species) enhancements were constant throughout the entire measurement period. Only one species, Larrea tridentata, decreased stomatal conductance by 25,50% in response to elevated CO2, and then only at the onset of the summer dry season and following late summer convective precipitation. Similarly, reductions in the maximum carboxylation rate of Rubisco were limited to Larrea during spring. These results suggest that the elevated CO2 response of desert vegetation is a function of complex interactions between species functional types and prevailing environmental conditions. Elevated CO2 did not extend the active growing season into the summer dry season because of overall negligible stomatal conductance responses that did not result in significant water conservation. Overall, we expect the greatest response of desert vegetation during years with above-average precipitation when the active growing season is not limited to ,2 months and, consequently, the effects of increased photosynthesis can accumulate over a biologically significant time period. [source] Plant,Water Relations of Kidney Bean Plants Treated with NaCl and Foliarly Applied GlycinebetaineJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 2 2002C. M. L. Lopez Salinity is at present one of the most serious environmental problems influencing crop growth. It has been extensively demonstrated that salinity affects several physiological processes in the plant, including the plant,water relations of most salt-sensitive crops species. In this study, the effects of salinity on the plant,water relations of kidney bean (Phaseolus vulgaris L.) and the possibility that foliarly applied glycinebetaine improves these water relations are examined. Kidney bean plants were grown in a greenhouse and treated with 0, 30, 50 and 100 mM NaCl, combined with 0, 10 and 30 mM glycinebetaine in foliar applications. Increased salinity levels decreased stomatal conductance, photosynthetic rate, transpiration and leaf relative water content in the 30, 50 and 100 mM treatments relative to the control treatment. Glycinebetaine applications of 10 mM increased stomatal conductance at 50 mM NaCl, ameliorating significantly the effect of salinity on water relations through increases in the leaf relative water content. At 100 mM NaCl, 30 mM glycinebetaine applications in particular contributed to osmotic stress, and had an adverse effect on plants. Our experiment suggests that glycinebetaine can be used as an alternative treatment to reduce the effects of salt stress on the water relations of salt-sensitive plants, but only to limited salinity levels. Furthermore, the improvement in the water status of kidney beans was dose dependent, suggesting that the concentration of glycinebetaine essential for the survival of salt-sensitive plants is species specific and must be determined individually for each plant species. Pflanzen,Wasser-Beziehungen von NaCl-behandelten und mit Glycinbetain besprühten Blättern von Gartenbohnenpflanzen Versalzung ist zur Zeit eine der am meisten wirksamen Umweltprobleme im Hinblick auf das Wachstum von Kulturpflanzen. Es hat umfangreiche Untersuchungen gegeben, die Versalzungswirkungen in ihrem Einfluss auf zahlreiche physiologische Vorgänge in der Pflanze zu untersuchen; hierbei wurden auch die Pflanzen,Wasser-Beziehungen von hochsalzempfindlichen Pflanzenarten berück-sichtigt. In dieser Untersuchung wurden die Einflüsse der Versalzung auf die Pflanzen,Wasser-Beziehungen bei Buschbohnen (Phaseolus vulgaris L.) und die Möglichkeit über Blattbesprühungen mit Glycinbetain die Wasser-Beziehungen zu verbessern, untersucht. Die Buschbohnen wurden im Gewächshaus angezogen und mit 0, 30, 50 mM NaCl in Kombination mit 0, 10, 30 mM Glycinbetain Blattbehandlungen angezogen. Eine Erhöhung der Versalzung führte zu einer Abnahme der stomatären Konduktanz, der Photosyntheserate, der Transpiration und des relativen Blattwassergehaltes bei den Behandlungen mit 30, 50 und 100 mM im Vergleich zur Kontrolle. Glysinbetainanwendungen von 10mM erhöhten die stomatäre Konduktanz bei 50 mM NaCl und verbesserten signifikant den ungünstigen Einfluss der Versalzung auf die Wasser-Beziehungen über eine Erhöhung des relativen Blattwassergehaltes. Verwendung von 100 mM NaCl und 30 mM GB trug zu dem osmotischen Streß durch Versalzung bei und hatten einen ungünstigen Einfluss auf die Pflanzen. Unser Experiment weist darauf hin, dass Glycinbetain eine alternative Möglichkeit ist, um die Einflüsse des Salzstresses auf die Wasser-Beziehungen von salzempfindlichen Pflanzen abzuschwächen; es bestehen aber Begrenzungen bezüglich des Versalzungsgrades, bei denen eine günstige Wirkung nachgewiesen werden kann. Ausserdem ist die Verbesserung im Wasserzustand der Buschbohnen von der Anwendungsstärke abhängig, so dass die Konzentration von GB wesentlich für das Überleben der salzempfindlichen Pflanzenart spezifisch ist und für jede Pflanzenart untersucht werden. [source] A model of stomatal conductance to quantify the relationship between leaf transpiration, microclimate and soil water stressPLANT CELL & ENVIRONMENT, Issue 11 2002Q. Gao Abstract A model of stomatal conductance was developed to relate plant transpiration rate to photosynthetic active radiation (PAR), vapour pressure deficit and soil water potential. Parameters of the model include sensitivity of osmotic potential of guard cells to photosynthetic active radiation, elastic modulus of guard cell structure, soil-to-leaf conductance and osmotic potential of guard cells at zero PAR. The model was applied to field observations on three functional types that include 11 species in subtropical southern China. Non-linear statistical regression was used to obtain parameters of the model. The result indicated that the model was capable of predicting stomatal conductance of all the 11 species and three functional types under wide ranges of environmental conditions. Major conclusions included that coniferous trees and shrubs were more tolerant for and resistant to soil water stress than broad-leaf trees due to their lower osmotic potential, lignified guard cell walls, and sunken and suspended guard cell structure under subsidiary epidermal cells. Mid-day depression in transpiration and photosynthesis of pines may be explained by decreased stomatal conductance under a large vapour pressure deficit. Stomatal conductance of pine trees was more strongly affected by vapour pressure deficit than that of other species because of their small soil-to-leaf conductance, which is explainable in terms of xylem tracheids in conifer trees. Tracheids transport water by means of small pit-pairs in their side walls, and are much less efficient than the end-perforated vessel members in broad-leaf xylem systems. These conclusions remain hypothetical until direct measurements of these parameters are available. [source] | ||||||||||