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  • 1
    Electronic Resource
    Electronic Resource
    Carbon and water balance in Polylepis sericea, a tropical treeline species (1996)
    Springer
    Trees 10 (1996), S. 218-222 
    Details
    ISSN: 0931-1890
    Keywords: Key words Carbon balance ; Polylepis sericea ; Treeline ; Tropical Andes ; Water balance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Polylepis sericea trees grow well above the continuous forest line in the Venezuelan Andes. In these environments, extreme daily temperature ranges can occur at any time of the year and trees experience a 4 month dry period. The purpose of this work was to study carbon and water relations of this species in the field during wet and dry seasons in order to understand this species’ success at such high altitudes. Leaf gas exchange (portable system in open mode) and leaf water potential (pressure chamber) were measured at 1 – 2 h intervals during several daily courses at 4000 m elevation in the Páramo de Piedras Blancas. CO2 assimilation versus leaf temperature curves were also obtained for this species in the laboratory. Clear differences in the measured parameters were observed between seasons. For a wet season day, maximum CO2 assimilation rate was 7.4 μmol m –  2 s –  1 and leaf conductance was relatively constant (approximately 100 mmol m –  2 s –  1). In the dry season day, maximum CO2 assimilation rate was 5.8 μmolm –  2s –  1 and leaf conductance was close to 60 mmolm –  2s –  1. Minimum leaf water potentials measured were  – 1.3 MPa for the wet and –2.2 MPa for the dry season. The CO2 assimilation-leaf temperature relationship showed a 13.4°C leaf temperature optimum for photosynthesis with maximum and minimum compensation points of 29.5 and –2.8°C, respectively. Maximum night-time respiration was relatively high (2.7 μmol m –  2 s –  1). Our results show that P. sericea maintains a highly positive carbon balance through all daily courses, even though there is a slight water stress effect during the dry season; this suggests that its carbon assimilation machinery is well adapted to the low temperatures and seasonal water stress found in the high tropical mountains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02185672
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  • 2
    Electronic Resource
    Electronic Resource
    How does a mistletoe affect the water, nitrogen and carbon balance of two mangrove ecosystem species? (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 13 (1990), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. The effect of a mistletoe, Phthirusa maritima, on the water, nitrogen and carbon balance of two mangrove host species, Conocarpus erectus and Coccoloba uvifera, was studied. Several daily cycles of water potential and its components (pressure-volume curves); leaf nitrogen content (Kjeldahl method); leaf conductance, transpiration rates and carbon assimilation (portable gas exchange system) were measured on mistletoe, infested and uninfested plants in the Caribbean coast of Venezuela. The mistletoe on both host species showed higher transpiration rates and lower CO2 assimilation rates, and therefore lower water use efficiencies. With respect to infested and uninfested plants, C. erectus did not show large differences in the parameters measured with the exception of assimilation rates which were significantly lower in the infested plants. On the other hand, C. uvifera did show differences in all parameters and, therefore, was affected to a greater degree by the mistletoe. The behaviour of mistletoeinfested and uninfested plants, with respect to habitats with different degrees of water stress and with respect to the salinity gradient in which these mangroves grow, is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1990.tb01984.x
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  • 3
    Electronic Resource
    Electronic Resource
    Low-temperature resistance in Polylepis tarapacana, a tree growing at the highest altitudes in the world (2001)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 24 (2001), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The Polylepis tarapacana forests found in Bolivia are unique with respect to their altitudinal distribution (4200–5200 m). Given the extreme environmental conditions that characterize these altitudes, this species has to rely on distinct mechanisms to survive stressful temperatures. The purpose of this study was to determine low-temperature resistance mechanisms in P. tarapacana. Tissue was sampled for carbohydrate and proline contents and micro-climatic measurements were made at two altitudes, 4300 and 4850 m, during both the dry cold and wet warm seasons. Supercooling capacity (−3 to −6 °C for the cold dry and −7 to −9 °C for the wet warm season) and injury temperatures (−18 to −23 °C for both seasons), determined in the laboratory, indicate that P. tarapacana is a frost-tolerant species. On the other hand, an increase in supercooling capacity, as the result of significant increase in total soluble sugar and proline contents, occurs during the wet warm season as a consequence of higher metabolic activity. Hence, P. tarapacana, a frost-tolerant species during the colder unfavourable season, is able to avoid freezing during the more favourable season when minimum night-time temperatures are not as extreme.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2001.00685.x
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  • 4
    Electronic Resource
    Electronic Resource
    Freezing avoidance in Andean giant rosette plants (1985)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 8 (1985), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Frost avoidance mechanisms were studied in Espeletia spicata and Espeletia timotensis, two Andean giant rosette species. The daily courses of soil, air and tissue temperatures were measured at a site at circa 4000 m. Only the leaves were exposed to subzero temperatures; the apical bud and stem pith tissues were insulated by surrounding tissues. The leaf tissues avoided freezing by supercooling rather than by undergoing active osmotic changes. The temperatures at which ice formed in the tissues (the supercooling points) coincided with injury temperatures indicating that Espeletia tissue does not tolerate any kind of ice formation. For insulated tissue (apical bud, stem pith, roots) the supercooling point was around - 5°C coinciding with the injury temperature. Supercooling points of about –13 to - 16°C were observed for leaves. These results contrast with those reported for Afroalpine giant rosettes which tolerate extracellular freezing. The significance of different adaptive responses of giant rosettes to similar cold tropical environments is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1985.tb01685.x
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  • 5
    Electronic Resource
    Electronic Resource
    Freezing tolerance and avoidance in high tropical Andean plants: Is it equally represented in species with different plant height? (1991)
    Springer
    Oecologia 86 (1991), S. 378-382 
    Details
    ISSN: 1432-1939
    Keywords: Cold resistance mechanisms ; Supercooling ; Life forms ; High tropical mountains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Freezing tolerance and avoidance were studied in several different sized species of the tropical high Andes (4200 m) to determine whether there was a relationship between plant height and cold resistance mechanisms. Freezing injury and supercooling capacity were determined in ground level plants (i.e. cushions, small rosettes and a perennial herb), intermediate height plants (shrubs and perennial herbs) and arborescent forms (i.e. giant rosettes and small trees). All ground-level plants showed tolerance as the main mechanism of resistance to cold temperatures. Arborescent forms showed avoidance mechanisms mainly through supercooling, while intermediate plants exhibited both. Insulation mechanisms to avoid low temperatures were present in the two extreme life-forms. We suggest that a combination of freezing tolerance and avoidance by insulation is least expensive and is a more secure mechanism for high tropical mountain plants than supercooling alone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317604
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  • 6
    Electronic Resource
    Electronic Resource
    Gas exchange and water balance of a mistletoe species and its mangrove hosts (1989)
    Springer
    Oecologia 78 (1989), S. 176-183 
    Details
    ISSN: 1432-1939
    Keywords: Mistletoes ; Mangrove trees ; Gas exchange ; Water relations ; Carbon isotope ratios
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The gas exchange and water relations of the hemiparasite Pthirusa maritima and two its mangrove host species, Conocarpus erectus and Coccoloba uvifera, were studied in an intertidal zone of the Venezuelan coast. Carbon uptake and transpiration, leaf osmotic and total water potential, as well as nutrient content in the xylem sap and leaves of mistletoes and hosts were followed through the dry and wet season. In addition, carbon isotope ratios of leaf tissue were measured to further evaluate water use efficiency. Under similar light and humidity conditions, mistletoes had higher transpiration rates, lower leaf water potentials, and lower water use efficiencies than their hosts. Potassium content was much higher in mistletoes than in host leaves, but mineral nutrient content in the xylem sap of mistletoes was relatively low. The resistance of the liquid pathway from the soil to the leaf surface of mistletoes was larger than the total liquid flow resistance of host plants. Differences in the daily cycles of osmotic potential of the xylem sap also indicate the existence of a high resistance pathway along the vascular connection between the parasite pathway along the vascular connection between the parasite and its host. P. maritima mistletoes adjust to the different physiological characteristics of the host species which it parasitizes, thus ensuring an adequate water and carbon balance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377153
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  • 7
    Electronic Resource
    Electronic Resource
    Cold hardiness and supercooling along an altitudinal gradient in andean giant rosette species (1985)
    Springer
    Oecologia 68 (1985), S. 147-152 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Factors affecting supercooling capacity and cold hardiness were investigated in leaves of ten giant rosette species of the genus Espeletia (Compositae). These species grow along a 2,800–4,200 m elevation gradient in the Venezuelan Andes. In this high tropical environment, freezing frequently occurs every night, particularly above 3,300 m, but lasts for only a few hours. Supercooling capacty is linearly related to leaf water potential (Ψ L ) in all species; however supercooling is more responsive to Ψ L changes in Espeletia species from high paramos. The rate of change in the species-specific supercooling point and the rate of change of average annual minimum temperature along the elevation and climatic gradient follow the same trend (approximately -0.6 K per 100 m elevation). At a given elevation, the expanded leaves of the different species tend to supercool 8–10 K below minimum air temperatures. Experimentally-induced freezing was accompanied by the formation of intracellular ice and tissue damage. The relative apoplastic water content (RAWC) of the leaves, which may influence the ice nucleation rate or the facility by which ice propagates, was determined by pressure-volume methods. Species from higher sites tend to exhibit lower RAWC (2%–7%) than species from lower sites (7%–36%). A causal relationship between supercooling capacity and RAWC is suggested. In the high tropical Andes, the temperature oxotherm plateau of Espeletia leaves seems to be sufficiently fow to avoid freezing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379487
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  • 8
    Electronic Resource
    Electronic Resource
    Freezing tolerance in Draba chionophila, a ‘miniature’ caulescent rosette species (1988)
    Springer
    Oecologia 75 (1988), S. 156-160 
    Details
    ISSN: 1432-1939
    Keywords: Draba chionophila ; Freezing tolerance ; Cold resistance ; High tropical mountains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Freezing tolerance as a cold resistance mechanism is described for the first time in a plant growing in the tropical range of the Andean high mountains. Draba chionophila, the plant in which freezing tolerance was found, is the vascular plant which reaches the highest altitudes in the Venezuelan Andes (approximately 4700m). Night cycles of air and leaf temperature were studied in the field to determine the temperature at which leaf freezing began. In the laboratory, thermal analysis and freezing injury determinations were also carried out. From both field and laboratory experiments, it was determined that freezing of the leaf tissue, as well as root and pith tissue, initiated at a temperature of approximately-5.0°C, while freezing injury occurred at approximately-12.0°C for the pith, and below-14.0°C for roots and leaves. This difference in temperature suggests that the plant still survives freezing in the-5.0 to-14.0°C range. Daily cycles of leaf osmotic potential and soluble carbohydrate concentration were also determined in an attempt to explain some of the changes occurring in this species during the nighttime temperature period. A comparison between Andean and African high mountain plants from the point of view of cold resistance mechanisms is made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00378830
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    Carbon and water balance in Polylepis sericea, a tropical treeline species (1996)
    Springer
    Trees 10 (1996), S. 218-222 
    Details
    ISSN: 1432-2285
    Keywords: Carbon balance ; Polylepis sericea ; Treeline ; Tropical Andes ; Water balance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Polylepis sericea trees grow well above the continuous forest line in the Venezuelan Andes. In these environments, extreme daily temperature ranges can occur at any time of the year and trees experience a 4 month dry period. The purpose of this work was to study carbon and water relations of this species in the field during wet and dry seasons in order to understand this species' success at such high altitudes. Leaf gas exchange (portable system in open mode) and leaf water potential (pressure chamber) were measured at 1–2 h intervals during several daily courses at 4000 m elevation in the Páramo de Piedras Blancas. CO2 assimilation versus leaf temperature curves were also obtained for this species in the laboratory. Clear differences in the measured parameters were observed between seasons. For a wet season day, maximum CO2 assimilation rate was 7.4 μmol m-2 s-1 and leaf conductance was relatively constant (approximately 100 mmol m-2 s-1)In the dry season day, maximum CO2 assimilation rate was 5.8 μmolm-2 s-1 and leaf conductance was close to 60 mmolm-2 s-1. Minimum leaf water potentials measured were -1.3 MPa for the wet and -2.2 MPa for the dry season. The CO2 assimilation-leaf temperature relationship showed a 13.4°C leaf temperature optimum for photosynthesis with maximum and minimum compensation points of 29.5 and -2.8°C, respectively. Maximum night-time respiration was relatively high (2.7 (imol) m-2 s-1)Our results show thatP. sericea maintains a highly positive carbon balance through all daily courses, even though there is a slight water stress effect during the dry season; this suggests that its carbon assimilation machinery is well adapted to the low temperatures and seasonal water stress found in the high tropical mountains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02185672
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    Paper (German National Licenses)
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