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  • 1
    Electronic Resource
    Electronic Resource
    Functional acclimation to solar UV-B radiation in Gunnera magellanica, a native plant species of southernmost Patagonia (2003)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 26 (2003), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The ecosystems of Tierra del Fuego (in southern Patagonia, Argentina) are seasonally exposed to elevated levels of ultraviolet-B radiation (UV-B: 280–315 nm), due to the passage of the ‘ozone hole’ over this region. In the experiments reported in this article the effects of solar UV-B and UV-A (315–400 nm) on two UV-B defence-related processes: the accumulation of protective UV-absorbing compounds and DNA repair, were tested. It was found that the accumulation of UV-absorbing sunscreens in Gunnera magellanica leaves was not affected by plant exposure to ambient UV radiation. Photorepair was the predominant mechanism of cyclobutane-pyrimidine dimer (CPD) removal in G. magellanica. Plants exposed to solar UV had higher CPD repair capacity under optimal conditions of temperature (25 °C) than plants grown under attenuated UV. There was no measurable repair at 8 °C. The rates of CPD repair in G. magellanica plants were modest in comparison with other species and, under equivalent conditions, were about 50% lower than the repair rates of Arabidopsis thaliana (Ler ecotype). Collectively our results suggest that the susceptibility of G. magellanica plants to current ambient levels of solar UV-B in southern Patagonia may be related to a low DNA repair capacity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.0016-8025.2003.01120.x
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of animal husbandry on herbivore-carrying capacity at a regional scale (1992)
    [s.l.] : Nature Publishing Group
    Nature 356 (1992), S. 234-236 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Our objectives were to assess the impact of human intervention on herbivore carrying capacity, to determine whether the close relationship between natural herbivore biomass and primary productivity observed across terrestrial habitats1'2 reflects a limitation imposed by primary production, and to ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/356234a0
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  • 3
    Electronic Resource
    Electronic Resource
    Large herbivores in rangelands (1993)
    [s.l.] : Nature Publishing Group
    Nature 364 (1993), S. 293-293 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] MCNAUGHTON ETAL. REPLY - Fritz and Duncan conclude that African pastoral and natural systems have similar carrying capacities for large herbivores. According to the data in the sources they cite, wild herbivore-soil-rainfall data are on a local basis in game reserves, while livestock-soil-rainfall ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/364293a0
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  • 4
    Electronic Resource
    Electronic Resource
    Resource partitioning between shrubs and grasses in the Patagonian steppe (1989)
    Springer
    Oecologia 81 (1989), S. 501-505 
    Details
    ISSN: 1432-1939
    Keywords: Resource partitioning ; Steppe ; Water use ; Shrubs ; Patagonia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Experiments were conducted in the Patagonian steppe in southern South America to test the following hypotheses: (a) grasses take up most of the water from the upper layers of the soil and utilize frequent and short-duration pulses of water availability; (b) shrubs, on the contrary, take up most of the water from the lower layers of the soil and utilize infrequent and long-duration pulses of water availability. Grasses and shrubs were removed selectively and the performance of plants and the availability of soil resources were monitored. Results supported the overall hypothesis that grasses and shrubs in the Patagonian steppe use mainly different resources. Removal of shrubs did not alter grass production but removal of grasses resulted in a small increase in shrub production which was mediated by an increase in deep soil water and in shrub leaf water potential. The efficiency of utilization of resources freed by grass removal was approximately 25%. Shrubs used water exclusively from lower soil layers. Grasses took up most of the water from upper layers but they were also capable of absorbing water from deep layers. This pattern of water partitioning along with the lack of response in leaf nitrogen to the removal treatments suggested that shrubs may be at a disadvantage to grasses with respect to nutrient capture and led to questions about the role of nutrient recirculation, leaching, and nitrogen fixation in the steppe.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00378959
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  • 5
    Electronic Resource
    Electronic Resource
    Rooting depth, water availability, and vegetation cover along an aridity gradient in Patagonia (1996)
    Springer
    Oecologia 108 (1996), S. 503-511 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00333727
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  • 6
    Electronic Resource
    Electronic Resource
    Differential use of large summer rainfall events by shrubs and grasses: a manipulative experiment in the Patagonian steppe (1998)
    Springer
    Oecologia 115 (1998), S. 17-25 
    Details
    ISSN: 1432-1939
    Keywords: Key words Patagonian steppe ; Water stress ; Percolation ; Aboveground net primary production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In the Patagonian steppe, years with above-average precipitation (wet years) are characterized by the occurrence of large rainfall events. The objective of this paper was to analyze the ability of shrubs and grasses to use these large events. Shrubs absorb water from the lower layers, grasses from the upper layers, intercepting water that would otherwise reach the layers exploited by shrubs. We hypothesized that both life-forms could use the large rainfalls and that the response of shrubs could be more affected by the presence of grasses than vice versa. We performed a field experiment using a factorial combination of water addition and life-form removal, and repeated it during the warm season of three successive years. The response variables were leaf growth, and soil and plant water potential. Grasses always responded to experimental large rainfall events, and their response was greater in dry than in wet years. Shrubs only used large rainfalls in the driest year, when the soil water potential in the deep layers was low. The presence or absence of one life-form did not modify the response of the other. The magnitude of the increase in soil water potential was much higher in dry than in humid years, suggesting an explanation for the differences among years in the magnitude of the response of shrubs and grasses. We propose that the generally reported poor response of deep-rooted shrubs to summer rainfalls could be because (1) the water is insufficient to reach deep soil layers, (2) the plants are in a dormant phenological status, and/or (3) deep soil layers have a high water potential. The two last situations may result in high deep-drainage losses, one of the most likely explanations for the elsewhere-reported low response of aboveground net primary production to precipitation during wet years.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050486
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  • 7
    Electronic Resource
    Electronic Resource
    Water status of soil and vegetation in a shortgrass steppe (1981)
    Springer
    Oecologia 48 (1981), S. 327-331 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In an attempt to describe some major relationships between soil and plant compartments in a shortgrass steppe, the process of water loss from the system and plant water relations throughout a drying cycle were studied. The water supply was manipulated and some soil and plant variables monitored throughout a drying cycle. Leaf conductance and leaf water potential of blue grama (Bouteloua gracilis) were measured periodically at predawn and noon. Soil water content and water potential of different layers were also monitored. Three different periods were distinguished in the water loss process throughout a drying cycle. These distinctions were made taking into account the relative contribution of different soil layers. Leaf conductance and water potential at noon slowly declined throughout the first 50 days of plant growth. After that, they rapidly decreased, reaching values of 0.29 mm s-1 and-5.0 MPa, respectively. The predawn leaf water potential remained unchanged around-0.5 MPa during the first 45 days, then rapidly decreased. This occurred when soil water of the wettest soil layer was near depletion. Predawn leaf water potentials were highly correlated with water potentials of the wettest layer. Leaf conductance and water potential at noon were correlated with effective soil water potential (soil water potential weighted by the root distribution in the profile). We concluded that root surface area limited the water flow through an important part of the day in this semiarid ecosystem. Axial root resistance did not appear important in determining the equilibrium status between leaves and the wettest soil layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00346489
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  • 8
    Electronic Resource
    Electronic Resource
    Maximum rooting depth of vegetation types at the global scale (1996)
    Springer
    Oecologia 108 (1996), S. 583-595 
    Details
    ISSN: 1432-1939
    Keywords: Deep roots function ; Terrestrial vegetation ; Biomes ; Plant forms ; Root depth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The depth at which plants are able to grow roots has important implications for the whole ecosystem hydrological balance, as well as for carbon and nutrient cycling. Here we summarize what we know about the maximum rooting depth of species belonging to the major terrestrial biomes. We found 290 observations of maximum rooting depth in the literature which covered 253 woody and herbaceous species. Maximum rooting depth ranged from 0.3 m for some tundra species to 68 m for Boscia albitrunca in the central Kalahari; 194 species had roots at least 2 m deep, 50 species had roots at a depth of 5 m or more, and 22 species had roots as deep as 10 m or more. The average for the globe was 4.6±0.5 m. Maximum rooting depth by biome was 2.0±0.3 m for boreal forest. 2.1±0.2 m for cropland, 9.5±2.4 m for desert, 5.2±0.8 m for sclerophyllous shrubland and forest, 3.9±0.4 m for temperate coniferous forest, 2.9±0.2 m for temperate deciduous forest, 2.6±0.2 m for temperate grassland, 3.7±0.5 m for tropical deciduous forest, 7.3±2.8 m for tropical evergreen forest, 15.0±5.4 m for tropical grassland/savanna, and 0.5±0.1 m for tundra. Grouping all the species across biomes (except croplands) by three basic functional groups: trees, shrubs, and herbaceous plants, the maximum rooting depth was 7.0±1.2 m for trees, 5.1±0.8 m for shrubs, and 2.6±0.1 m for herbaceous plants. These data show that deep root habits are quite common in woody and herbaceous species across most of the terrestrial biomes, far deeper than the traditional view has held up to now. This finding has important implications for a better understanding of ecosystem function and its application in developing ecosystem models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00329030
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  • 9
    Electronic Resource
    Electronic Resource
    Ecosystem water fluxes for two grasslands in elevated CO2: a modeling analysis (1998)
    Springer
    Oecologia 113 (1998), S. 537-546 
    Details
    ISSN: 1432-1939
    Keywords: Key words Drainage ; Ecosystem water budget ; Leaf area index ; Soil evaporation ; Plant transpiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The need to combine data from CO2 field experiments with climate data remains urgent, particularly because each CO2 experiment cannot run for decades to centuries. Furthermore, predictions for a given biome need to take into account differences in productivity and leaf area index (LAI) independent of CO2-derived changes. In this study, we use long-term weather records and field data from the Jasper Ridge CO2 experiment in Palo Alto, California, to model the effects of CO2 and climate variability on ecosystem water fluxes. The sandstone and serpentine grasslands at Jasper Ridge provide a range of primary productivity and LAI, with the sandstone as the more productive system. Modeled soil water availability agreed well with published observations of time-domain reflectometry in the CO2 experiment. Simulated water fluxes based on 10-year weather data (January 1985–December 1994) showed that the sandstone grassland had a much greater proportion of water movement through plants than did the serpentine; transpiration accounted for approximately 30% of annual fluxes in the sandstone and only 10% in the serpentine. Although simulated physiological and biomass changes were similar in both grasslands, the consequences of elevated CO2 were greater for the sandstone water budget. Elevated CO2 increased soil drainage by 20% in the sandstone, despite an approximately one-fifth increase in plant biomass; in the serpentine, drainage increased by 〈10% and soil evaporation was unchanged for the same simulated biomass change. Phenological changes, simulated by a 15-day lengthening of the growing season, had minimal impacts on the water budget. Annual variation in the timing and amount of rainfall was important for water fluxes in both grasslands. Elevated CO2 increased sandstone drainage 〉50 mm in seven of ten years, but the relative increase in drainage varied from 10% to 300% depending on the year. Early-season transpiration in the sandstone decreased between 26% and 41%, with elevated CO2 resulting in a simulated water savings of 54–76 mm. Even in years when precipitation was similar (e.g., 505 and 479 mm in years 3 and 4), the effect of CO2 varied dramatically. The response of grassland water budgets to CO2 depends on the productivity and structure of the grassland, the amount and timing of rainfall, and CO2-induced changes in physiology. In systems with low LAI, large physiological changes may not necessarily alter total ecosystem water budgets dramatically.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050407
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  • 10
    Electronic Resource
    Electronic Resource
    A global analysis of root distributions for terrestrial biomes (1996)
    Springer
    Oecologia 108 (1996), S. 389-411 
    Details
    ISSN: 1432-1939
    Keywords: Terrestrial biomes ; Cumulative root fraction ; Root biomass ; Rooting density ; Soil depth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Understanding and predicting ecosystem functioning (e.g., carbon and water fluxes) and the role of soils in carbon storage requires an accurate assessment of plant rooting distributions. Here, in a comprehensive literature synthesis, we analyze rooting patterns for terrestrial biomes and compare distributions for various plant functional groups. We compiled a database of 250 root studies, subdividing suitable results into 11 biomes, and fitted the depth coefficient β to the data for each biome (Gale and Grigal 1987). β is a simple numerical index of rooting distribution based on the asymptotic equation Y=1-βd, where d = depth and Y = the proportion of roots from the surface to depth d. High values of β correspond to a greater proportion of roots with depth. Tundra, boreal forest, and temperate grasslands showed the shallowest rooting profiles (β=0.913, 0.943, and 0.943, respectively), with 80–90% of roots in the top 30 cm of soil; deserts and temperate coniferous forests showed the deepest profiles (β=0.975 and 0.976, respectively) and had only 50% of their roots in the upper 30 cm. Standing root biomass varied by over an order of magnitude across biomes, from approximately 0.2 to 5 kg m-2. Tropical evergreen forests had the highest root biomass (5 kg m-2), but other forest biomes and sclerophyllous shrublands were of similar magnitude. Root biomass for croplands, deserts, tundra and grasslands was below 1.5 kg m-2. Root/shoot (R/S) ratios were highest for tundra, grasslands, and cold deserts (ranging from 4 to 7); forest ecosystems and croplands had the lowest R/S ratios (approximately 0.1 to 0.5). Comparing data across biomes for plant functional groups, grasses had 44% of their roots in the top 10 cm of soil. (β=0.952), while shrubs had only 21% in the same depth increment (β=0.978). The rooting distribution of all temperate and tropical trees was β=0.970 with 26% of roots in the top 10 cm and 60% in the top 30 cm. Overall, the globally averaged root distribution for all ecosystems was β=0.966 (r 2=0.89) with approximately 30%, 50%, and 75% of roots in the top 10 cm, 20 cm, and 40 cm, respectively. We discuss the merits and possible shortcomings of our analysis in the context of root biomass and root functioning.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00333714
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