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  • Reproduction  (2)
  • Root distribution  (2)
  • 1
    ISSN: 1432-1939
    Keywords: Patagonia-vegetation ; Root distribution ; 13C-, 18O-, D-Isotope composition ; Water ; Plant succession
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Above-and belowground biomass distribution, isotopic composition of soil and xylem water, and carbon isotope ratios were studied along an aridity gradient in Patagonia (44–45°S). Sites, ranging from those with Nothofagus forest with high annual rainfall (770 mm) to Nothofagus scrub (520 mm), Festuca (290 mm) and Stipa (160 mm) grasslands and into desert vegetation (125 mm), were chosen to test whether rooting depth compensates for low rainfall. Along this gradient, both mean above-and belowground biomass and leaf area index decreased, but average carbon isotope ratios of sun leaves remained constant (at-27‰), indicating no major differences in the ratio of assimilation to stomatal conductance at the time of leaf growth. The depth of the soil horizon that contained 90% of the root biomass was similar for forests and grasslands (about 0.80–0.50 m), but was shallower in the desert (0.30 m). In all habitats, roots reached water-saturated soils or ground water at 2–3 m depth. The depth profile of oxygen and hydrogen isotope ratios of soil water corresponded inversely to volumetric soil water contents and showed distinct patterns throughout the soil profile due to evaporation, water uptake and rainfall events of the past year. The isotope ratios of soil water indicated that high soil moisture at 2–3 m soil depth had originated from rainy periods earlier in the season or even from past rainy seasons. Hydrogen and oxygen isotope ratios of xylem water revealed that all plants used water from recent rain events in the topsoil and not from water-saturated soils at greater depth. However, this study cannot explain the vegetation zonation along the transect on the basis of water supply to the existing plant cover. Although water was accessible to roots in deeper soil layers in all habitats, as demonstrated by high soil moisture, earlier rain events were not fully utilized by the current plant cover during summer drought. The role of seedling establishment in determining species composition and vegetation type, and the indirect effect of seedling establishment on the use of water by fully developed plant cover, are discussed in relation to climate change and vegetation modelling.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 70 (1986), S. 172-177 
    ISSN: 1432-1939
    Keywords: Water use ; Root distribution ; Water potential predawn ; Leaf conductance ; Quercus durata ; Heteromeles arbutifolia ; Adenostoma fasciculatum ; Rhamnus californica
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mixed stands of chaparral in California usually contain several species of shrubs growing close to each other so that aerial branches and subterranean roots overlap. There is some evidence that roots are stratified relative to depth. It may be that root stratification promotes sharing of soil moisture resources. We examined this possibility by comparing seasonal water use patterns in a mixed stand of chaparral dominated by four species of shrubs: Quercus durata, Heteromeles arbutifolia, Adenostoma fasciculatum, and Rhamnus californica. We used a neutron probe and soil phychrometers to follow seasonal depletion and recharging of soil moisture and compared these patterns to seasonal patterns of predawn water potentials, diurnal leaf conductances, and diurnal leaf water potentials. Our results indicated that 1) Quercus was deeply rooted, having high water potentials and high leaf conductances throughout the summer drought period, 2) Heteromeles/Adenostoma were intermediate in rooting depth, water potentials, and leaf conductances, and 3) Rhamnus was shallow rooted, having the lowest water potentials and leaf conductances. During the peak of the drought, predawn water potentials for Quercus corresponded to soil water potentials at or below a depth of 2 m, predawn water potentials of Heteromeles/ Adenostoma corresponded to a depth of 0.75 m, and predawn water potentials of Rhamnus corresponded to a depth of 0.5 m. This study supports the concept that co-occurring shrubs of chaparral in California utilize a different base of soil moisture resources.
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  • 3
    ISSN: 1432-1939
    Keywords: Serpentine ; Annuals ; Water-use ; Nitrogenuse ; Reproduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mediterranean-climate annuals growing on serpentine soils in central California differ greatly in their life spans and reproductive periods dependent on their access to soil moisture. The longer-lived annuals accumulate a greater lifetime biomass, have a higher total, but lower proportional, reproductive output, and produce leaves with a higher C/N ratios at the time of reproduction.
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  • 4
    ISSN: 1432-1939
    Keywords: Annual grassland ; Avena barbata CO2 ; Reproduction ; Water relations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Global atmospheric CO2 is increasing at a rate of 1.5–2 ppm per year and is predicted to double by the end of the next century. Understanding how terrestrial ecosystems will respond in this changing environment is an important goal of current research. Here we present results from a field study of elevated CO2 in a California annual grassland. Elevated CO2 led to lower leaf-level stomatal conductance and transpiration (approximately 50%) and higher mid-day leaf water potentials (30–35%) in the most abundant species of the grassland, Avena barbata Brot. Higher CO2 concentrations also resulted in greater midday photosynthetic rates (70% on average). The effects of CO2 on stomatal conductance and leaf water potential decreased towards the end of the growing season, when Avena began to show signs of senescence. Water-use efficiency was approximately doubled in elevated CO2, as estimated by instantaneous gas-exchange measurements and seasonal carbon isotope discrimination. Increases in CO2 and photosynthesis resulted in more seeds per plant (30%) and taller and heavier plants (27% and 41%, respectively). Elevated CO2 also reduced seed N concentrations (9%).
    Type of Medium: Electronic Resource
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