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  • 1
    Electronic Resource
    Electronic Resource
    Effects of manipulation of water and nitrogen regime on the water relations of the desert shrub Larrea tridentata (1988)
    Springer
    Oecologia 77 (1988), S. 480-486 
    Details
    ISSN: 1432-1939
    Keywords: Larrea tridentata ; Water relations ; Nitrogen fertilization ; Stomata ; Canopy transpiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Water and nitrogen regimes of Larrea tridentata shrubs growing in the field were manipulated during an annual cycle. Patterns of leaf water status, leaf water relations characteristics, and stomatal behavior were followed concurrently. Large variations in leaf water status in both irrigated and nonirrigated individuals were observed. Predawn and midday leaf water potentials of nonirrigated shrubs were lowest except when measurements had been preceded by significant rainfall. Despite the large seasonal variation in leaf water status, reasonably constant, high levels of turgor were maintained. Pressure-volume curve analysis suggested that changes in the bulk leaf osmotic potential at full turgor were small and that nearly all of the turgor adjustment was due to tissue elastic adjustment. The increase in tissue elasticity with increasing water deficit manifested itself as a decrease in the relative water content at zero turgor and as a decrease in the tissue bulk elastic modulus. Because of large hydration-induced displacement in the osmotic potential and relative water content at zero turgor, it was necessary to use shoots in their natural state of hydration for pressure-volume curve determinations. Large diurnal and seasonal differences in maximum stomatal conductance were observed, but could not easily be attributed to variations in leaf water potential or leaf water relations characteristics such as the turgor loss point. The single factor which seemed to account for most of the diurnal and seasonal differences in maximum stomatal conductance between individual shrubs was an index of soil/root/ shoot hydraulic resistance. Daily maximum stomatal conductance was found to decrease with increasing soil/root/ shoot hydraulic resistance. This pattern was most consistent if the hydraulic resistance calculation was based on an estimate of total canopy transpiration rather than the more commonly used transpiration per unit leaf area. The reasons for this are discussed. It is suggested that while stomatal aperture necessarily represents a major physical resistance controlling transpiration, plant hydraulic resistance may represent the functional resistance through its effects on stomatal aperture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377263
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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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