			Home About us Contact

Gas Exchange Parameters (gas + exchange_parameter)

Distribution by Scientific Domains

Life Sciences	60%

Selected Abstracts

Relationship between Carbon Isotope Discrimination, Mineral Content and Gas Exchange Parameters in Vegetative Organs of Wheat Grown under Three Different Water Regimes

JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 3 2010
L. Zhu
Abstract Carbon isotope discrimination (,) has been proposed as an indirect selection criterion for transpiration efficiency and grain yield in wheat. However, because of high cost for , analysis, attempts have been made to identify alternative screening criteria. Ash content (ma) has been proposed as an alternative criterion for , in wheat and barley. A pot experiment was conducted to analyse the relationship between ,, mineral content and gas exchange parameters in seedlings and leaves of bread wheat (Triticum aestivum L.). Plants of 10 genotypes were cultivated under three different water regimes corresponding to moderate (T3), intermediate (T2) and severe drought (T1) stress obtained by maintaining soil humidity at 75 %, 55 % and 45 % of the humidity at field capacity respectively. , and ma in seedlings and leaves showed significant differences among the three water treatments. Significant positive correlations were found between , and ma in seedlings and leaves at elongation and anthesis stages in severe drought stress (T1). , was negatively associated with potassium (K) content in intermediate drought stress (T2) and positively with magnesium (Mg) content in T2 and T3 (moderate drought stress) in flag leaf at anthesis. There were negative correlations between , and single-leaf intrinsic water-use efficiency (WT) in T2 and T3 at anthesis stage. Stronger positive associations were noted between , and stomatal conductance (gs) in T1 and T2 than in T3 at anthesis. These results suggested that , is a good trait as an indirect selection criterion for genotypic improvement in transpiration efficiency, while ma is a possible alternative criterion of , in wheat vegetative organs, especially in stressed environments. Significant association was found between , and K, Mg and Ca contents that would merit being better investigated. [source]

Biomass and leaf-level gas exchange characteristics of three African savanna C4 grass species under optimum growth conditions

AFRICAN JOURNAL OF ECOLOGY, Issue 4 2009
K. B. Mantlana
Abstract C4 savanna grass species, Digitaria eriantha, Eragrostis lehmanniana and Panicum repens, were grown under optimum growth conditions with the aim of characterizing their above- and below-ground biomass allocation and the response of their gas exchange to changes in light intensity, CO2 concentration and leaf-to-air vapour pressure deficit gradient (Dl). Digitaria eriantha showed the largest above- and below-ground biomass, high efficiency in carbon gain under light-limiting conditions, high water use efficiency (WUE) and strong stomatal sensitivity to Dl (P = 0.002; r2 = 0.5). Panicum repens had a high aboveground biomass and attained high light saturated photosynthetic rates (Asat, 47 ,mol m,2 s,1), stomatal conductance, (gsat, 0.25 mol m,2 s,1) at relatively high WUE. Eragrostis lehmanniana had almost half the biomass of other species, and had similar Asat and gsat but were attained at lower WUE than the other species. This species also showed the weakest stomatal response to Dl (P = 0.19, r2 = 0. 1). The potential ecological significance of the contrasting patterns of biomass allocation and variations in gas exchange parameters among the species are discussed. Résumé On a fait pousser des espèces herbeuses de savane de type C4, Digitaria eriantha, Eragrostis lehmanniana et Panicum repens, dans des conditions optimales dans le but de caractériser l'allocation de leur biomasse aérienne et racinaire et la réponse de leur échange gazeux à des changements d'intensité de la lumière, de concentrations de CO2, et à un gradient déficitaire (Dl) de pression de vapeur feuille-air. D. eriantha montrait la plus grande biomasse aérienne et racinaire, une grande efficience de l'assimilation de carbone dans des conditions de luminosité limitée, une grande efficience d'utilisation de l'eau (WUE) et une forte sensibilité des stomates à Dl (P = 0,002; r2 = 0,5). P. repens avait une grande biomasse aérienne et atteignait des taux photosynthétiques élevés en lumière saturée (Asat, 47 ,mol m,2 s,1), et une conductance stomatique (gsat 0.25 mol m,2 s,1) à une WUE relativement élevée. E. lehmanniana avait une biomasse qui était presque la moitié de celle des autres espèces et avait un Asat et un gsat similaires mais qui étaient atteints à une WUE plus basse que les autres espèces. Cette espèce montrait aussi la plus faible réponse stomatique àDl (P = 0,19, r2 = 0,1). L'on discute de la signification écologique potentielle de ces schémas contrastés d'allocations de biomasse et des variations des paramètres des échanges gazeux entre les espèces. [source]

Evidence that Branch Cuvettes are Reasonable Surrogates for Estimating O3 Effects in Entire Tree Crowns

PLANT BIOLOGY, Issue 2 2007
C. Then&
Abstract: Within the scope of quantifying ozone (O3) effects on forest tree crowns it is still an open question whether cuvette branches of adult trees are reasonable surrogates for O3 responses of entire tree crowns and whether twigs exhibit autonomy in defense metabolism in addition to carbon autonomy. Therefore, cuvette-enclosed branches of mature beech (Fagus sylvatica) trees were compared with branches exposed to the same and different ozone regimes by a free-air fumigation system under natural stand conditions by means of a vice versa experiment. For this purpose, cuvettes receiving 1 × O3 air were mounted in trees exposed to 2 × O3 and cuvettes receiving 2 × O3 air were mounted in trees exposed to 1 × O3 in the upper sun crown. At the end of the fumigation period in September 2004, leaves were examined for differences in gas exchange parameters, pigments, antioxidants, carbohydrates, and stable isotope ratios. No significant differences in foliar gas exchange, total carbohydrates, stable isotope ratios, pigment, and antioxidant contents were found as a consequence of cuvette enclosure (cuvette versus free-air branches) of the same O3 concentrations besides increase of glucose inside the cuvettes and reduction of the de-epoxidation state of the xanthophyll cycle pigments. No significant ozone effect was found for the investigated gas exchange and most biochemical parameters. The total and oxidized glutathione level of the leaves was increased by the 2 × O3 treatment in the cuvette and the free-air branches, but this effect was significant only for the free-air branches. From these results we conclude that cuvette branches are useful surrogates for examining the response of entire tree crowns to elevated O3 and that the defence metabolism of twigs seems to be at least partially autonomous. [source]

Sexual dimorphism and seasonal changes of leaf gas exchange in the dioecious tree Ilex paraguariensis grown in two contrasted cultivation types

ANNALS OF APPLIED BIOLOGY, Issue 2 2009
M. Rakocevic
Abstract Yerba maté (Ilex paraguariensis, Aquifoliaceae) is a subtropical, evergreen, dioecious, South American tree. In one preliminary study, it was observed that the functional strategy of yerba mate females, aiming to finish reproductive process, was increased transpiration relative to photosynthetic rates compared with males, on self-shaded leaves. We hypothesised that the long-term gas exchange response of males and females can evolve independently of phenological stage and cultivation type. In this spirit, the primary aim of the study was to analyse the physiological sexual dimorphism of this species, evaluating fluctuations of gas exchanges related to microclimate and phenological stages. A field study was conducted on adult plants of yerba maté cultivated in monoculture (MO) and in forest understorey (FUS), and measurements carried out in situ on microclimate and leaf gas exchange parameters. The photosynthetic photon flux density that was attained at leaf level in FUS was reduced roughly 10-fold compared with that in MO. Various leaf age populations were observed during a 2-year period at 2-month intervals and grouped into four categories: young, young-fully-expanded, fully-expanded and old. Young and young-fully-expanded leaves were the most active in photosynthesis. Leaves of female plants showed greater photosynthetic rate than those of male plants, which was expressed on all leaf age categories in MO, but only during vegetative stages previous to flowering and fruit ripening. The photosynthesis of young-fully-expanded leaves of females grown in FUS was superior to males but only during winter growth pause. The stomatal conductance differed in relation to cultivation type and leaf age but did not show the sexual differentiation. Physiological sexual dimorphism in yerba mate is shown to be plastic, responding to environmental conditions. The cost associated to the reproduction of yerba maté could be most easily met showing physiological differentiation of both sexes. A higher reproductive investment of females might be compensated for by exhibiting greater leaf photosynthesis than males that occurs in vegetative stages that precede flowering and fruit ripening. [source]