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  • 1
    Electronic Resource
    Electronic Resource
    Ecophysiology of two solar tracking desert winter annuals (1982)
    Springer
    Oecologia 54 (1982), S. 41-49 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The seasonal course of water relations in field populations of two leaf solar tracking desert winter annuals was examined. Measurements were made of leaf movements in relation to leaf conductance and water potential. Malvastrum rotundifolium maintained solar tracking movements up to the wilting point of the plant (-4 MPa). Lupinus arizonicus altered its morphology through paraheliotropic leaf movements as leaf water potentials declined to-1.8 MPa. Diurnal patterns of leaf conductance showed marked seasonal trends, with gas exchange activity being restricted to early morning hours as water availability declined. Studies of potted plants showed that L. arizonicus was not able to alter its osmotic potential in response to drought, while M. rotundifolium underwent a 1.86 MPa reduction in osmotic potential. The significance of the two contrasting patterns is discussed in terms of observed plant distribution and origin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00541105
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  • 2
    Electronic Resource
    Electronic Resource
    Solar tracking response to drought in a desert annual (1980)
    Springer
    Oecologia 44 (1980), S. 159-163 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The responses to drought of the solar tracking winter annualLupinus arizonicus (Wats.) were examined under field and laboratory growth regimes. Under drought conditions tracking movements were maintained until the plant reached the wilting point. The leaves and leaflets were observed to cup in response to decreases in the xylem water potential. This resulted in a negative, but linear relationship between the cosine of the angle of incidence of the direct solar beam upon the leaf and water potential. Leaf conductance was also significantly related to xylem water potential in natural populations. Leaf and leaflet cupping seem to be responding directly to changing plant water status, resulting in reduced solar radiation load to drought stressed plants. It is hypothesized that this property may have adaptive consequences in relation to the water relations, energy budget, and carbon balance of the plant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00572673
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  • 3
    Electronic Resource
    Electronic Resource
    Ecophysiology of two solar tracking desert winter annuals (1983)
    Springer
    Oecologia 57 (1983), S. 344-351 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The gas exchange responses of potted, outdoor and greenhouse grown plants of the Sonoran Desert annuals Lupinus arizonicus (Wats.) and Malvastrum rotundifolium (Gray) were examined. Light saturation of leaf photosynthetic rates did not occur in either species at quantum flux densities exceeding 2.0 mmol m-2 s-1. Decreasing water potentials due to long-term drought did not alter this pattern of light response, though it did lower both photosynthetic rates and leaf conductances. Absolute maximum net photosynthetic rates exceeded 60 μmol m-2 s-1 and 50 μmol m-2 s-1 for M. rotundifolium and L. arizonicus, respectively. Both species showed a two level control of leaf conductance, responding to bulk leaf water potential and vapor pressure deficit. There were non-stomatal effects of drought upon photosynthesis in each species. Leaves of M. rotundifolium exhibited a constant stomatal, inhibition of approximately 19%, while in leaves of L. arizonicus stomatal inhibition ranged from 12–40% with decreasing leaf water potentials. These physiological data lend support to previous reports on the divergent water use patterns of these co-occurring species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377179
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  • 4
    Electronic Resource
    Electronic Resource
    Ecophysiology of two solar tracking desert winter annuals (1983)
    Springer
    Oecologia 58 (1983), S. 10-18 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary This paper represents an empirical study on the effect of different leaf orientations on the daily carbon gain and transpirational water loss of desert winter annuals. Laboratory physiological data on Malvastrum rotundifolium (Gray) and Lupinus arizonicus (Wats) were combined with energy budget concepts and field measurements of water relations and leaf movements to predict carbon gain patterns for horizontally oriented, diaheliotropic and paraheliotropic leaf movement types. The results showed contrasting patterns of carbon gain and water loss. L. arizonicus, which is capable of both dia- and paraheliotropic leaf movements, had the lowest rates of daily carbon gain and water loss. But these low rates resulted in the highest water use efficiencies under early season conditions and high water availability. M. rotundifolium, a diaheliotropic species, was predicted as having the highest rates of carbon gain and water loss on a daily basis over a wide range of environmental conditions and water availability. Despite possessing the highest rates for transpiration, its water use efficiency was higher in relation to other leaf movement types, under a variety of conditions. This result was extremely sensitive to soil water availability. The results were discussed in relation to the ecological ramifications of leaf movements in arid land annuals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00384536
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  • 5
    Electronic Resource
    Electronic Resource
    Interseasonal comparison of CO2 concentrations, isotopic composition, and carbon dynamics in an Amazonian rainforest (French Guiana) (1997)
    Springer
    Oecologia 110 (1997), S. 120-131 
    Details
    ISSN: 1432-1939
    Keywords: Key words Carbon discrimination  ;  δ13C  ;  δ18O  ;  Canopy CO2 profiles  ;  Soil respiration.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Canopy CO2 concentrations in a tropical rainforest in French Guiana were measured continuously for 5 days during the 1994 dry season and the 1995 wet season. Carbon dioxide concentrations ([CO2]) throughout the canopy (0.02–38 m) showed a distinct daily pattern, were well-stratified and decreased with increasing height into the canopy. During both seasons, daytime [CO2] in the upper and middle canopy decreased on average 7–10 μmol mol−1 below tropospheric baseline values measured at Barbados. Within the main part of the canopy (≥ 0.7 m), [CO2] did not differ between the wet and dry seasons. In contrast, [CO2] below 0.7 m were generally higher during the dry season, resulting in larger [CO2] gradients. Supporting this observation, soil CO2 efflux was on average higher during the dry season than during the wet season, either due to diffusive limitations and/or to oxygen deficiency of root and microbial respiration. Soil respiration rates decreased by 40% after strong rain events, resulting in a rapid decrease in canopy [CO2] immediately above the forest floor of about 50␣μmol mol−1. Temporal and spatial variations in [CO2]canopy were reflected in changes of δ13Ccanopy and δ18Ocanopy values. Tight relationships were observed between δ13C and δ18O of canopy CO2 during both seasons (r 2 〉 0.86). The most depleted δ13Ccanopy and δ18Ocanopy values were measured immediately above the forest floor (δ13C = −16.4‰; δ18O = 39.1‰ SMOW). Gradients in the isotope ratios of CO2 between the top of the canopy and the forest floor ranged between 2.0‰ and 6.3‰ for δ13C, and between 1.0‰ and 3.5‰ for δ18O. The δ13Cleaf and calculated c i/c a of foliage at three different positions were similar for the dry and wet seasons indicating that the canopy maintained a constant ratio of photosynthesis to stomatal conductance. About 20% of the differences in δ13Cleaf within the canopy was accounted for by source air effects, the remaining 80% must be due to changes in c i/c a. Plotting 1/[CO2] vs. the corresponding δ13C ratios resulted in very tight, linear relationships (r 2 = 0.99), with no significant differences between the two seasons, suggesting negligible seasonal variability in turbulent mixing relative to ecosystem gas exchange. The intercepts of these relationships that should be indicative of the δ13C of respired sources were close to the measured δ13C of soil respired CO2 and to the δ13C of litter and soil organic matter. Estimates of carbon isotope discrimination of the entire ecosystem, Δe, were calculated as 20.3‰ during the dry season and as 20.5‰ during the wet season.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050140
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  • 6
    Electronic Resource
    Electronic Resource
    Hydrogen and oxygen isotope ratios of tree ring cellulose for field-grown riparian trees (2000)
    Springer
    Oecologia 123 (2000), S. 481-489 
    Details
    ISSN: 1432-1939
    Keywords: Key words δD ; δ18O ; Cellulose modeling ; Humidity ; Water source
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The isotopic composition of tree ring cellulose was obtained over a 2-year period from small-diameter riparian-zone trees at field sites that differed in source water isotopic composition and humidity. The sites were located in Utah (cool and low humidity), Oregon (cool and high humidity), and Arizona (warm and low humidity) with source water isotope ratio values of –125/–15‰ (δD/δ18O), –48/–6‰, and –67/–7‰, respectively. Monthly environmental measurements included temperature and humidity along with measurements of the isotope ratios in atmospheric water vapor, stream, stem, and leaf water. Small riparian trees used only stream water (both δD and δ18O of stem and stream water did not differ), but δ values of both atmospheric water vapor and leaf water varied substantially between months. Differences in ambient temperature and humidity conditions between sites contributed to substantial differences in leaf water evaporative enrichment. These leaf water differences resulted in differences in the δD and δ18O values of tree ring cellulose, indicating that humidity information was recorded in the annual rings of trees. These environmental and isotopic measurements were used to test a mechanistic model of the factors contributing to δD and δ18O values in tree ring cellulose. The model was tested in two parts: (a) a leaf water model using environmental information to predict leaf water evaporative enrichment and (b) a model describing biochemical fractionation events and isotopic exchange with medium water. The models adequately accounted for field observations of both leaf water and tree ring cellulose, indicating that the model parameterization from controlled experiments was robust even under uncontrolled and variable field conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420000349
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  • 7
    Electronic Resource
    Electronic Resource
    Leaf hairs: Effects on physiological activity and adaptive value to a desert shrub (1978)
    Springer
    Oecologia 37 (1978), S. 183-200 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The effects of leaf hairs on photosynthesis, transpiration, and leaf energy balance were measured on the desert shrub Encelia farinosa in order to determine the adaptive significance of the hairs. The pubescence reduces leaf absorptance resulting in a reduced heat load, and as a consequence lower leaf temperatures and lower transpiration rates. In its native habitat where air temperatures often exceed 40° C, the optimum temperature for photosynthesis in E. farinosa occurs at 25° C, and at leaf temperatures above 35° C net photosynthesis declines precipitously. An advantage of leaf pubescence is that it allows a leaf temperature much lower than air temperature. As a result, leaf temperatures are near the temperature optimum for photosynthesis and high, potentially lethal leaf temperatures are avoided. However, there is a disadvantage associated with leaf pubescence. By reflecting quanta that might otherwise be used in photosynthesis, the presence of leaf hairs reduces the rate of photosynthesis. A tradeoff model was used to assess the overall advantage of possessing leaf hairs. In terms of the carbon gaining capacity of the leaf, the model predicted that for different environmental conditions different levels of leaf pubescence were optimal. In other words, under aird conditions and/or high air temperatures, leaves of E. farinosa would have a higher rate of photosynthesis by being pubescent than by not being pubescent. The predictions from this model agreed closely with observed patterns of leaf pubescence in the field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00344990
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  • 8
    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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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Leaf carbon isotope discrimination and nitrogen content for riparian trees along elevational transects (1997)
    Springer
    Oecologia 109 (1997), S. 362-367 
    Details
    ISSN: 1432-1939
    Keywords: Key words Stable isotope ; Carbon isotope ratio ; Carbon isotope discrimination ; Riparian ecosystem ; Water-use efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Leaf carbon isotope discrimination (Δ), seasonal estimates of the leaf-to-air water vapor gradient on a molar basis (ω), and leaf nitrogen contents were examined in three riparian tree species (Populus fremontii, P. angustifolia, and Salix exigua) along elevational transects in northern and southern Utah USA (1500–2670 m and 600–1820 m elevational gradients, respectively). The ω values decreased with elevation for all species along transects. Plants growing at higher elevations exhibited lower Δ values than plants at lower elevations (P. fremontii, 22.9‰ and 19.5‰, respectively; P. angustifolia, 23.2‰ and 19.2‰, respectively; and S.␣exigua, 21.1‰ and 19.1‰, respectively). Leaf nitrogen content increased with elevation for all species, suggesting that photosynthetic capacity at a given intercellular carbon dioxide concentration was greater at higher elevations. Leaf Δ and nitrogen content values were highly correlated, implying that leaves with higher photosynthetic capacities also had lower intercellular carbon dioxide concentrations. No significant interannual differences were detected in carbon isotope discrimination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050094
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