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  • 1
    Electronic Resource
    Electronic Resource
    Stem water storage and diurnal patterns of water use in tropical forest canopy trees (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 21 (1998), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Stem water storage capacity and diurnal patterns of water use were studied in five canopy trees of a seasonal tropical forest in Panama. Sap flow was measured simultaneously at the top and at the base of each tree using constant energy input thermal probes inserted in the sapwood. The daily stem storage capacity was calculated by comparing the diurnal patterns of basal and crown sap flow. The amount of water withdrawn from storage and subsequently replaced daily ranged from 4 kg d–1 in a 0·20-m-diameter individual of Cecropia longipes to 54 kg d–1 in a 1·02-m-diameter individual of Anacardium excelsum, representing 9–15% of the total daily water loss, respectively. Ficus insipida, Luehea seemannii and Spondias mombin had intermediate diurnal water storage capacities. Trees with greater storage capacity maintained maximum rates of transpiration for a substantially longer fraction of the day than trees with smaller water storage capacity. All five trees conformed to a common linear relationship between diurnal storage capacity and basal sapwood area, suggesting that this relationship was species-independent and size-specific for trees at the study site. According to this relationship there was an increment of 10 kg of diurnal water storage capacity for every 0·1 m2 increase in basal sapwood area. The diurnal withdrawal of water from, and refill of, internal stores was a dynamic process, tightly coupled to fluctuations in environmental conditions. The variations in basal and crown sap flow were more synchronized after 1100 h when internal reserves were mostly depleted. Stem water storage may partially compensate for increases in axial hydraulic resistance with tree size and thus play an important role in regulating the water status of leaves exposed to the large diurnal variations in evaporative demand that occur in the upper canopy of seasonal lowland tropical forests.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1998.00273.x
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  • 2
    Electronic Resource
    Electronic Resource
    Control of transpiration from the upper canopy of a tropical forest: the role of stomatal, boundary layer and hydraulic architecture components (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 20 (1997), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Concurrent, independent measurements of stomatal conductance (gs), transpiration (E) and microenvironmental variables were used to characterize control of crown transpiration in four tree species growing in a moist, lowland tropical forest. Access to the upper forest canopy was provided by a construction crane equipped with a gondola. Estimates of boundary layer conductance (gb) obtained with two independent methods permitted control of E to be partitioned quantitatively between gs and gb using a dimensionless decoupling coefficient (Ω) ranging from zero to 1. A combination of high gs (c. 300–600 mmol m−2 s−1) and low wind speed, and therefore relatively low gb (c. 100–800 mmol m−2 s−1), strongly decoupled E from control by stomata in all four species (Ω= 0.7–0.9). Photosynthetic water-use efficiency was predicted to increase rather than decrease with increasing gs because gb was relatively low and internal conductance to CO2 transfer was relatively high. Responses of gs to humidity were apparent only when the leaf surface, and not the bulk air, was used as the reference point for determination of external vapour pressure. However, independent measurements of crown conductance (gc), a total vapour phase conductance that included stomatal and boundary layer components, revealed a clear decline in gc with increasing leaf-to-bulk air vapour pressure difference (Va because the external reference points for determination of gc and Va were compatible. The relationships between gc and Vc and between gs and Vs appeared to be distinct for each species. However, when gs and gc were normalized by the branch-specific ratio of leaf area to sapwood area (LA/SA), a morphological index of potential transpirational demand relative to water transport capacity, a common relationship between conductance and evaporative demand for all four species emerged. Taken together, these results implied that, at a given combination of LA/SA and evaporative demand scaled to the appropriate reference point, the vapour phase conductance and therefore transpiration rates on a leaf area basis were identical in all four contrasting species studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1997.d01-26.x
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  • 3
    Electronic Resource
    Electronic Resource
    Subacute combined degeneration of the spinal cord: MRI detection of preferential involvement of the posterior columns in a child (1995)
    Springer
    Pediatric radiology 25 (1995), S. 140-141 
    Details
    ISSN: 1432-1998
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Subacute combined degeneration of the spinal cord (vitamin B12-deficient myelopathy) is a neurologic disorder manifesting progressive symptoms of paresthesia and spastic paralysis. As shown by pathology, it initially involves the posterior columns of the thoracic cord. We present a case of vitamin B12 deficiency with preferential posterior column involvement of the thoracic cord in a child. Theoretically, this should be the earliest, most reversible stage of the disease, making recognition of this MRI pattern of critical importance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02010329
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  • 4
    Electronic Resource
    Electronic Resource
    Growth, biomass allocation and photosynthesis of invasive and native Hawaiian rainforest species (1998)
    Springer
    Oecologia 117 (1998), S. 449-459 
    Details
    ISSN: 1432-1939
    Keywords: Key words Invasive species ; Photosynthesis ; Biomass allocation ; Hawaii ; Tropical rain forests
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Growth, biomass allocation, and photosynthetic characteristics of seedlings of five invasive non-indigenous and four native species grown under different light regimes were studied to help explain the success of invasive species in Hawaiian rainforests. Plants were grown under three greenhouse light levels representative of those found in the center and edge of gaps and in the understory of Hawaiian rainforests, and under an additional treatment with unaltered shade. Relative growth rates (RGRs) of invasive species grown in sun and partial shade were significantly higher than those for native species, averaging 0.25 and 0.17 g g−1 week−1, respectively, while native species averaged only 0.09 and 0.06 g g−1 week−1, respectively. The RGR of invasive species under the shade treatment was 40% higher than that of native species. Leaf area ratios (LARs) of sun and partial-shade-grown invasive and native species were similar but the LAR of invasive species in the shade was, on average, 20% higher than that of native species. There were no differences between invasive and native species in biomass allocation to shoots and roots, or in leaf mass per area across light environments. Light-saturated photosynthetic rates (Pmax) were higher for invasive species than for native species in all light treatments. Pmax of invasive species grown in the sun treatment, for example, ranged from 5.5 to 11.9 μmol m−2 s−1 as compared with 3.0−4.5 μmol m−2 s−1 for native species grown under similar light conditions. The slope of the linear relationship between Pmax and dark respiration was steeper for invasive than for native species, indicating that invasive species assimilate more CO2 at a lower respiratory cost than native species. These results suggest that the invasive species may have higher growth rates than the native species as a consequence of higher photosynthetic capacities under sun and partial shade, lower dark respiration under all light treatments, and higher LARs when growing under shade conditions. Overall, invasive species appear to be better suited than native species to capturing and utilizing light resources, particularly in high-light environments such as those characterized by relatively high levels of disturbance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050680
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  • 5
    Electronic Resource
    Electronic Resource
    Leaf construction cost, nutrient concentration, and net CO2 assimilation of native and invasive species in Hawaii (1999)
    Springer
    Oecologia 121 (1999), S. 183-192 
    Details
    ISSN: 1432-1939
    Keywords: Key words Cost of construction ; Life forms ; Nitrogen use efficiency ; Photosynthesis ; Specific leaf area
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of biological invasions are most evident in isolated oceanic islands such as the Hawaiian Archipelago, where invasive plant species are rapidly changing the composition and function of plant communities. In this study, we compared the specific leaf area (SLA), leaf tissue construction cost (CC), leaf nutrient concentration, and net CO2 assimilation (A) of 83 populations of 34 native and 30 invasive species spanning elevation and substrate age gradients on Mauna Loa volcano in the island of Hawaii. In this complex environmental matrix, where annual precipitation is higher than 1500 mm, we predicted that invasive species, as a group, will have leaf traits, such as higher SLA and A and lower leaf CC, which may result in more efficient capture of limiting resources (use more resources at a lower carbon cost) than native species. Overall, invasive species had higher SLA and A, and lower CC than native species, consistent with our prediction. SLA and foliar N and P were 22.5%, 30.5%, and 37.5% higher, respectively, in invasive species compared to native ones. Light-saturated photosynthesis was higher for invasive species (9.59 μmol m−2 s−1) than for native species (7.31 μmol m−2 s−1), and the difference was larger when A was expressed on a mass basis. Leaf construction costs, on the other hand, were lower for the invasive species (1.33 equivalents of glucose g−1) than for native species (1.37). This difference was larger when CC was expressed on an area basis. The trends in the above traits were maintained when groups of ecologically equivalent native and invasive species (i.e., sharing similar life history traits and growing in the same habitat) were compared. Foliar N and P were significantly higher in invasive species across all growth forms. Higher N may partially explain the higher A of invasive species. Despite relatively high N, the photosynthetic nitrogen use efficiency of invasive species was 15% higher than that of native species. These results suggest that invasive species may not only use resources more efficiently than native species, but may potentially demonstrate higher growth rates, consistent with their rapid spread in isolated oceanic islands.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050920
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  • 6
    Electronic Resource
    Electronic Resource
    Environmental and physiological regulation of transpiration in tropical forest gap species: the influence of boundary layer and hydraulic properties (1995)
    Springer
    Oecologia 101 (1995), S. 514-522 
    Details
    ISSN: 1432-1939
    Keywords: Tropical forest ; Transpiration ; Stomata ; Boundary layer ; Hydraulic conductance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Environmental and physiological regulation of transpiration were examined in several gap-colonizing shrub and tree species during two consecutive dry seasons in a moist, lowland tropical forest on Barro Colorado Island, Panama. Whole plant transpiration, stomatal and total vapor phase (stomatal + boundary layer) conductance, plant water potential and environmental variables were measured concurrently. This allowed control of transpiration (E) to be partitioned quantitatively between stomatal (g s) and boundary layer (g b) conductance and permitted the impact of invividual environmental and physiological variables on stomatal behavior and E to be assessed. Wind speed in treefall gap sites was often below the 0.25 m s−1 stalling speed of the anemometer used and was rarely above 0.5 m s−1, resulting in uniformly low g b (c. 200–300 mmol m−2 s−1) among all species studied regardless of leaf size. Stomatal conductance was typically equal to or somewhat greater than g b. This strongly decoupled E from control by stomata, so that in Miconia argentea a 10% change in g s when g s was near its mean value was predicted to yield only a 2.5% change in E. Porometric estimates of E, obtained as the product of g s and the leaf-bulk air vapor pressure difference (VPD) without taking g b into account, were up to 300% higher than actual E determined from sap flow measurements. Porometry was thus inadequate as a means of assessing the physiological consequences of stomatal behavior in different gap colonizing species. Stomatal responses to humidity strongly limited the increase in E with increasing evaporative demand. Stomata of all species studied appeared to respond to increasing evaporative demand in the same manner when the leaf surface was selected as the reference point for determination of external vapor pressure and when simultaneous variation of light and leaf-air VPD was taken into account. This result suggests that contrasting stomatal responses to similar leaf-bulk air VPD may be governed as much by the external boundary layer as by intrinsic physiological differences among species. Both E and g s initially increased sharply with increasing leaf area-specific total hydraulic conductance of the soil/root/leaf pathway (G t), becoming asymptotic at higher values of G t. For both E and g s a unique relationship appeared to describe the response of all species to variations in G t. The relatively weak correlation observed between g s and midday leaf water potential suggested that stomatal adjustment to variations in water availability coordinated E with water transport efficiency rather than bulk leaf water status.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00329432
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  • 7
    Electronic Resource
    Electronic Resource
    Physiological and morphological variation in Metrosideros polymorpha, a dominant Hawaiian tree species, along an altitudinal gradient: the role of phenotypic plasticity (1998)
    Springer
    Oecologia 113 (1998), S. 188-196 
    Details
    ISSN: 1432-1939
    Keywords: Key wordsMetrosideros polymorpha ; Phenotypic plasticity ; Photosynthesis ; Carbon isotope ratios ; Photosynthetic nitrogen use efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Metrosideros polymorpha, a dominant tree species in Hawaiian ecosystems, occupies a wide range of habitats. Complementary field and common-garden studies of M. polymorpha populations were conducted across an altitudinal gradient at two different substrate ages to ascertain if the large phenotypic variation of this species is determined by genetic differences or by phenotypic modifications resulting from environmental conditions. Several characteristics, including ecophysiological behavior and anatomical features, were largely induced by the environment. However, other characteristics, particularly leaf morphology, appeared to be mainly determined by genetic background. Common garden plants exhibited higher average rates of net assimilation (5.8 μmol CO2 m−2 s−1) and higher average stomatal conductance (0.18 mol H2O m−2 s−1) than their field counterparts (3.0 μmol CO2 m−2 s−1, and 0.13 mol H2O m−2 s−1 respectively). Foliar δ13C of most common-garden plants was similar among sites of origin with an average value of −26.9‰. In contrast, mean values of foliar δ13C in field plants increased substantially from −29.5‰ at low elevation to −24.8‰ at high elevation. Leaf mass per unit area increased significantly as a function of elevation in both field and common garden plants; however, the range of values was much narrower in common garden plants (211–308 g m−2 for common garden versus 107–407 g m−2 for field plants). Nitrogen content measured on a leaf area basis in common garden plants ranged from 1.4 g m−2 to 2.4 g m−2 and from 0.8 g m−2 to 2.5 g m−2 in field plants. Photosynthetic nitrogen use efficiency (PNUE) decreased 50% with increasing elevation in field plants and only 20% in plants from young substrates in the common garden. This was a result of higher rates of net CO2 assimilation in the common garden plants. Leaf tissue and cell layer thickness, and degree of leaf pubescence increased significantly with elevation in field plants, whereas in common garden plants, variation with elevation of origin was much narrower, or was entirely absent. Morphological characteristics such as leaf size, petiole length, and internode length decreased with increasing elevation in the field and were retained when grown in the common garden, suggesting a potential genetic basis for these traits. The combination of environmentally induced variability in physiological and anatomical characteristics and genetically determined variation in morphological traits allows Hawaiian M. polymorpha to attain and dominate an extremely wide ecological distribution not observed in other tree species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050367
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  • 8
    Electronic Resource
    Electronic Resource
    Photosynthetic gas exchange and temperature-induced damage in seedlings of the tropical alpine species Argyroxiphium sandwicense (1996)
    Springer
    Oecologia 106 (1996), S. 298-307 
    Details
    ISSN: 1432-1939
    Keywords: Argyroxiphium sandwicense ; Photosynthesis ; Seedlings ; Supercooling ; Temperature acclimation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The capacity of Argyroxiphium sandwicense (silverword) seedlings to acclimate photosynthetic processes to different growing temperatures, as well as the tolerance of A. sandwicense to temperatures ranging from −15 to 60° C, were analyzed in a combination of field and laboratory studies. Altitudinal changes in temperature were also analyzed in order to explain the observed spatial distribution of A. sandwicense. A. sandwicense (Asteraceae) is a giant rosette plant that grows at high elevation on two Hawaiian volcanoes, where nocturnal subzero temperatures frequently occur. In addition, the soil temperatures at midday in the open alpine vegetation can exceed 60° C. In marked contrast to this large diurnal temperature variation, the seasonal variation in temperature is very small due to the tropical maritime location of the Hawaiian archipelago. Diurnal changes of soil and air temperature as well as photosynthetic photon flux density were measured on Haleakala volcano during four months. Seedlings were grown in the laboratory, from seeds collected in ten different A. sandwicense populations on Haleakala volcano, and maintained in growth chambers at 15/5, 25/15, and 30/25° C day/night temperatures. Irreversible tissue damage was determined by measuring electrolyte leakage of leaf samples. For seedlings maintained at each of the three different day/night temperatures, tissue damage occurred at −10° C due to freezing and at about 50° C due to high temperatures. Tissue damage occurred immediately after ice nucleation suggesting that A. sandwicense seedlings tend to avoid ice formation by permanent supercooling. Seedlings maintained at different day/night temperatures had similar maximum photosynthetic rates (5 μmol m−2 s−1) and similar optimum temperatures for photosynthesis (about 16° C). Leaf dark respiration rates compared at identical temperatures, however, were substantially higher for seedlings maintained at low temperatures, but almost perfect homeostasis is observed when compared at their respective growing conditions. The lack of acclimation in terms of frost resistance and tolerance to high temperatures, as well as in terms of the optimum temperature for photosynthesis, may contribute to the restricted altitudinal range of A. sandwicense. The small seasonal temperature variations in the tropical environment where this species grows may have prevented the development of mechanisms for acclimation to longterm temperature changes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00334557
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  • 9
    Electronic Resource
    Electronic Resource
    Partitioning of water resources among plants of a lowland tropical forest (1995)
    Springer
    Oecologia 101 (1995), S. 197-203 
    Details
    ISSN: 1432-1939
    Keywords: Stable hydrogen isotope composition ; δD Lowland tropical forest ; Water resource partitioning Transpiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Source water used by plants of several species in a semi-evergreen lowland tropical forest on Barro Colorado Island, Panama, was assessed by comparing the relative abundance of deuterium, D, versus hydrogen, H (stable hydrogen isotope composition, δD) in xylem sap and in soil water at different depths, during the dry season of 1992. Ecological correlates of source water were examined by comparing xylem water δD values with leaf phenology, leaf water status determined with a pressure chamber, and rates of water use determined as mass flow of sap using the stem heat balance method. Soil water δD values decreased sharply to 30 cm, then remained relatively constant with increasing depth. Average δD values were-13‰, for 0–30 cm depth and-36.7‰ for 30–100 cm depth. Soil water δD values were negatively associated with soil water content and soil water potential. Concurrent analyses of xylem water revealed a high degree of partitioning of water resources among species of this tropical forest. Xylem water δD of deciduous trees (average=-25.3±1.4‰) was higher than that of evergreen trees (average=-36.3±3.5‰), indicating that evergreen species had access to the more abundant soil water at greater depth than deciduous species. In evergreen shade-tolerant and high-light requiring shrubs and small trees, δD of xylem water was negatively correlated with transpiration rate and leaf water potential indicating that species using deeper, more abundant water resources had both higher rates of water use and more favorable leaf water status.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317284
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