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  • 1
    Electronic Resource
    Electronic Resource
    Environmental and physiological regulation of transpiration in tropical forest gap species: the influence of boundary layer and hydraulic properties (1995)
    Springer
    Oecologia 101 (1995), S. 514-522 
    Details
    ISSN: 1432-1939
    Keywords: Tropical forest ; Transpiration ; Stomata ; Boundary layer ; Hydraulic conductance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Environmental and physiological regulation of transpiration were examined in several gap-colonizing shrub and tree species during two consecutive dry seasons in a moist, lowland tropical forest on Barro Colorado Island, Panama. Whole plant transpiration, stomatal and total vapor phase (stomatal + boundary layer) conductance, plant water potential and environmental variables were measured concurrently. This allowed control of transpiration (E) to be partitioned quantitatively between stomatal (g s) and boundary layer (g b) conductance and permitted the impact of invividual environmental and physiological variables on stomatal behavior and E to be assessed. Wind speed in treefall gap sites was often below the 0.25 m s−1 stalling speed of the anemometer used and was rarely above 0.5 m s−1, resulting in uniformly low g b (c. 200–300 mmol m−2 s−1) among all species studied regardless of leaf size. Stomatal conductance was typically equal to or somewhat greater than g b. This strongly decoupled E from control by stomata, so that in Miconia argentea a 10% change in g s when g s was near its mean value was predicted to yield only a 2.5% change in E. Porometric estimates of E, obtained as the product of g s and the leaf-bulk air vapor pressure difference (VPD) without taking g b into account, were up to 300% higher than actual E determined from sap flow measurements. Porometry was thus inadequate as a means of assessing the physiological consequences of stomatal behavior in different gap colonizing species. Stomatal responses to humidity strongly limited the increase in E with increasing evaporative demand. Stomata of all species studied appeared to respond to increasing evaporative demand in the same manner when the leaf surface was selected as the reference point for determination of external vapor pressure and when simultaneous variation of light and leaf-air VPD was taken into account. This result suggests that contrasting stomatal responses to similar leaf-bulk air VPD may be governed as much by the external boundary layer as by intrinsic physiological differences among species. Both E and g s initially increased sharply with increasing leaf area-specific total hydraulic conductance of the soil/root/leaf pathway (G t), becoming asymptotic at higher values of G t. For both E and g s a unique relationship appeared to describe the response of all species to variations in G t. The relatively weak correlation observed between g s and midday leaf water potential suggested that stomatal adjustment to variations in water availability coordinated E with water transport efficiency rather than bulk leaf water status.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00329432
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Carbon isotope composition in relation to leaf gas exchange and environmental conditions in Hawaiian Metrosideros polymorpha populations (1992)
    Springer
    Oecologia 91 (1992), S. 305-311 
    Details
    ISSN: 1432-1939
    Keywords: Carbon isotope ratio ; Gas exchange ; Metrosideros ; Nitrogen-use efficiency ; Water-use efficiency ; Bog
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Carbon isotope composition, photosynthetic gas exchange, and nitrogen content were measured in leaves of three varieties of Metrosideros polymorpha growing in sites presenting a variety of precipitation, temperature and edaphic regimes. The eight populations studied could be divided into two groups on the basis of their mean foliar δ13C values, one group consisting of three populations with mean δ13C values ca.-26‰ and another group with δ13C values ca.-28‰. Less negative δ13C values appeared to be associated with reduced physiological availability of soil moisture resulting from hypoxic conditions at a poorly drained high elevation bog site and from low precipitation at a welldrained, low elevation leeward site. Gas exchange measurements indicated that foliar δ13C and intrinsic wateruse efficiency were positively correlated. Maximum photosynthetic rates were nearly constant while maximum stomatal conductance varied substantially in individuals with foliar δ13C ranging from-29 to-24‰. In contrast with the patterns of δ13C observed, leaf nitrogen content appeared to be genetically determined and independent of site characteristics. Photosynthetic nitrogenuse efficiency was nearly constant over the range of δ13C observed, suggesting that a compromise between intrinsic water- and N-use efficiency did not occur. In one population variations in foliar δ13C and gas exchange with leaf cohort age, caused the ratio of intercellular to atmospheric partial pressure of CO2 predicted from gas exchange and that calculated from δ13C to be in close agreement only in the two youngest cohorts of fully expanded leaves. The results indicated that with suitable precautions concerning measurement protocol, foliar δ13C and gas exchange measurements were reliable indicators of potential resource use efficiency by M. polymorpha along environmental gradients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317617
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Gas exchange and water balance of a mistletoe species and its mangrove hosts (1989)
    Springer
    Oecologia 78 (1989), S. 176-183 
    Details
    ISSN: 1432-1939
    Keywords: Mistletoes ; Mangrove trees ; Gas exchange ; Water relations ; Carbon isotope ratios
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The gas exchange and water relations of the hemiparasite Pthirusa maritima and two its mangrove host species, Conocarpus erectus and Coccoloba uvifera, were studied in an intertidal zone of the Venezuelan coast. Carbon uptake and transpiration, leaf osmotic and total water potential, as well as nutrient content in the xylem sap and leaves of mistletoes and hosts were followed through the dry and wet season. In addition, carbon isotope ratios of leaf tissue were measured to further evaluate water use efficiency. Under similar light and humidity conditions, mistletoes had higher transpiration rates, lower leaf water potentials, and lower water use efficiencies than their hosts. Potassium content was much higher in mistletoes than in host leaves, but mineral nutrient content in the xylem sap of mistletoes was relatively low. The resistance of the liquid pathway from the soil to the leaf surface of mistletoes was larger than the total liquid flow resistance of host plants. Differences in the daily cycles of osmotic potential of the xylem sap also indicate the existence of a high resistance pathway along the vascular connection between the parasite pathway along the vascular connection between the parasite and its host. P. maritima mistletoes adjust to the different physiological characteristics of the host species which it parasitizes, thus ensuring an adequate water and carbon balance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377153
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    Paper (German National Licenses)
    Fulltext
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