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  • Aboveground net primary production  (1)
  • Basal area  (1)
  • Cumulative root fraction  (1)
  • Ecosystem water budget  (1)
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  • 1
    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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    Paper (German National Licenses)
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  • 2
    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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    Paper (German National Licenses)
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  • 3
    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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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Grazing effects upon plant community structure in subhumid grasslands of Argentina (1986)
    Springer
    Plant ecology 67 (1986), S. 27-32 
    Details
    ISSN: 1573-5052
    Keywords: Argentina ; Basal area ; Community structure ; Diversity ; Dynamics ; Flooding pampa ; Grassland ; Grazing effect ; Leaf area
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Changes in plant community structure are identified as a result of grazing in grasslands of the flooding pampa which evolved under supposedly light grazing conditions. The effect of excluding grazing upon total leaf area index was an increase of 30%. The largest response was observed in the distribution of leaves in the canopy. In the grazed areas, most of the green material was concentrated in the 0–5 cm layer while in the ungrazed treatments the largest portion of the leaf area was in the 10–30 cm layer. Grazing exclusion resulted in a small change in total basal area but a larger change in its distribution, from many small tussocks to less numerous large ones. The effect of grazing upon leaf area and basal area was accounted for by changes in vigor as well as by changes in species composition. The major effect of excluding grazing upon species composition was the disappearance of some native planophile species and most of the exotics. The species composition of grazed areas of both communities was very similar while there were large differences between the ungrazed areas and between the grazed and ungrazed areas of the same community. It is suggested that there is a group of species which responds to the coarse-grained ‘signal’ of grazing and its presence can cause dissimilar communities to converge under grazing conditions. The other group of species responded to the fine-grained ‘signal’ of the environmental conditions associated with topography.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00040315
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    Paper (German National Licenses)
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