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Digitale Medien

Rooting depth, water availability, and vegetation cover along an aridity gradient in Patagonia (1996)

Schulze, E. -D. ; Mooney, H. A. ; Sala, O. E. ; [weitere]

Springer

Oecologia 108 (1996), S. 503-511

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ISSN: 1432-1939

Schlagwort(e): Patagonia-vegetation ; Root distribution ; 13C-, 18O-, D-Isotope composition ; Water ; Plant succession

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: 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.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00333727

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Digitale Medien

Water and nitrogen dynamics in an arid woodland (1994)

Evans, R. D. ; Ehleringer, J. R.

Springer

Oecologia 99 (1994), S. 233-242

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ISSN: 1432-1939

Schlagwort(e): Cryptobiotic crust ; Desert ecology ; Nitrogen cycle ; Stable isotopes ; Water source

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Abstract Arid environments are characterized by spatial and temporal variation in water and nitrogen availability. differences in δ15N and δD of four co-occurring species reveal contrasting patterns of plant resource acquisition in response to this variation. Mineralization potential and nitrogen concentration of surface soils associated with plant canopies were greater than inter-canopy locations, and values decreased with increasing depth in both locations. Mineralization potential and nitrogen concentration were both negatively correlated with soil δ15N. The spatial variation in soil δ15N caused corresponding changes in plant δ15N such that plant δ15N values were negatively correlated with nitrogen concentration of surface soils. Plants occurring on soils with relatively high nitrogen concentrations had lower δ15N, and higher leaf nitrogen concentrations, than plants occurring on soils with relatively low nitrogen concentrations. Two general temporal patterns of water and nitrogen use were apparent. Three species (Juniperus, Pinus andArtemisia) relied on the episodic availability of water and nitrogen at the soil surface. δ15N values did not vary through the year, while xylem pressure potentials and stem-water δD values fluctuated with changes in soil moisture at the soil surface. In contrast,Chrysothamnus switched to a more stable water and nitrogen source during drought. δ15N values ofChrysothamnus increased throughout the year, while xylem pressure potentials and stem-water δD values remained constant. The contrasting patterns of resource acquisition have important implications for community stability following disturbance. Disturbance can cause a decrease in nitrogen concentration at the soil surface, and so plants that rely on surface water and nitrogen may be more susceptible than those that switch to more stable water and nitrogen sources at depth during drougnt.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00627735

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Digitale Medien

Water relations of stem succulent trees in north-central Baja California (1990)

Nilsen, E. T. ; Sharifi, M. R. ; Rundel, P. W. ; [weitere]

Springer

Oecologia 82 (1990), S. 299-303

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ISSN: 1432-1939

Schlagwort(e): Succulent ; C3 trees ; Capacitance ; Baja California ; Idria collumnaris

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary Water relations of several stem succulent trees were measured in north-central Baja California in comparisons to other growth forms in the same habitat. Our research concentrated on three stem succulent species (Idria collumnaris, Pachycormus discolor and Bursera microphylla) each with a different succulent stem morphology. The stem succulent trees had 1 to 4 kg H2O/m3 of trunk while the other trees and shrubs in the same habitat had 0.6 to 0.8 kg H2O/m3. The diurnal and seasonal variation in leaf water potential was small for the stem succulent species in comparison to deciduous and evergreen species as a consequence of the stem-water, buffering capacity. In addition, the leaf conductance of the stem succulent species was low (60 mmol m−2 s−1) and yet, the leaf conductance decreased through the day similar to adjacent evergreen and deciduous species. The leaves of the stem succulent trees lost turgor at low saturated water deficits (0.06 to 0.14), had comparatively high osmotic potentials, and high values of elastic modulus in comparison to adjacent evergreen and deciduous species. The stem acts as an important buffering mechanism allowing for the maintenance of leaf turgor in these stem succulent trees. The low transpiration rates of the stem succulent trees may be a mechanism to minimize leaf saturated water deficit and extend leaf longevity.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00317474

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