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Featured researches published by Ch. Körner.


Oecologia | 1991

Carbon isotope discrimination by plants follows latitudinal and altitudinal trends

Ch. Körner; Graham D. Farquhar; S. C. Wong

SummaryIn an earlier paper we provided evidence that carbon isotope discrimination during photosynthesis of terrestrial C3 plants decreases with altitude, and it was found that this was associated with greater carboxylation efficiency at high altitudes. Changing partial pressures of CO2 and O2 and changing temperature are possible explanations, since influences of moisture and light were reduced to a minimum by selective sampling. Here we analyse plants sampled using the same criteria, but from high and low altitudes along latitudinal gradients from the equator to the polar ends of plant distribution. These data should permit separation of the pressure and temperature components (Fig. 1). Only leaves of fully sunlit, non-water-stressed, herbaceous C3 plants are compared. The survey covers pressure differences of 400 mbar (ca. 5000 m) and 78 degrees of latitude (ca 25 K of mean temperature of growth period). When habitats of similar low temperature (i.e. high altitude at low latitude and low altitude at polar latitude) are compared, discrimination increases towards the pole (with decreasing altitude and thus increasing atmospheric pressure). Latitudinally decreasing temperature at almost constant atmospheric pressure (samples from low altitude) is associated with a decrease in discrimination. So, polar low-altitude plants have δ13C values half way between humid tropical lowland and tropical alpine plants. It is unlikely that latitudinal changes of the light regime had an effect, since low and high altitude plants show contrasting latitudinal trends in δ13C although local altitudinal differences in overall light consumption were small. These results suggest that both temperature and atmospheric pressure are responsible for the altitudinal trends in 13C discrimination. Temperature effects may partly be related to increased leaf thickness (within the same leaf type) in cold environments. Theoretical considerations and laboratory experiments suggest that it is the oxygen partial pressure that is responsible for the pressure related change in discrimination. The study also provided results of practical significance for the use of carbon isotope data. Within a community of C3 plants, discrimination in species of similar life form, exposed to similar light, water and ambient CO2 conditions ranges over 4‰, with standard deviations for 10–30 species of ±0.6 to 1.2‰. This natural variation has to be taken into account by using a sufficient sample size and standardization of sampling in any attempt at ecological site characterization using carbon isotope data. Evidence of a pronounced genotypic component of this variation in 13C discrimination in wild C3 plant species is provided. Correlations with dry matter partitioning, mesophyll thickness and nitrogen content are also present.


Oecologia | 1988

A global survey of carbon isotope discrimination in plants from high altitude

Ch. Körner; Graham D. Farquhar; Z. Roksandic

SummaryCarbon 13/12 isotope ratios have been determined from leaves of a hundred C3 plant species (or ecotypes) from all major mountain ranges of the globe, avoiding drought stressed areas. A general increase in 13C content was found with increasing altitude, i.e. overall discrimination against the heavy isotope is reduced at high elevation. The steepest decline of discrimination is observed in taxa typically ranging to highest elevations (e.g. the genus Ranunculus). Mean δ 13C for all samples collected between 2500 and 5600 m altitude is-26.15‰ compared to the lowland average of-28.80‰ (P<0.001). Forbs from highest elevations reach-24‰. According to theory of 13C discrimination this indicates decreasing relative limitation of carbon uptake by carboxylation. In other words, we estimate that the ratio of internal to external partial pressure of CO2 (pi/pa)in leaves of high elevation plants is lower than in leaves of low altitude. These results confirm recent gas exchange analyses in high and low elevation plants.


Functional Ecology | 1987

In situ photosynthetic responses to light, temperature and carbon dioxide in herbaceous plants from low and high altitude

Ch. Körner; M. Diemer

Net CO2 assimilation (A) was analysed in situ in 12 pairs of altitudinally separated, herbaceous plant species in the Austrian Alps at 600 and 2600m. Both groups of species show a similar average response to light, saturating at quantum flux densities (400-700mm) (QFD) of more than 1200 VLmol m-2 sol. Temperature optimum of QFD-saturated A differs little (3K) and corresponds to the median of air temperature at leaf level for hours with rate-saturating light conditions and not to mean air temperature which differs by 10K. Species with an exclusive high altitude distribution show steeper initial slopes and higher levels of saturation of the response of A to internal partial pressure of CO2 (CPI) than low elevation species. Mean A at local ambient partial pressure (CPA) does not differ between sites (c. 18 VLmol m-2 s-1), despite the 21% decrease in atmospheric pressure. Plants at high altitude operate at mean CPJ of 177 debar as compared to 250 debar at low altitude. The higher ECU (efficiency of carbon dioxide uptake [linear slope of A/CPJ curve]) as well as the steeper CO2 gradient between mesophyll and ambient air of alpine plants are explained by (1) greater leaf and palisade layer thickness and (2) greater nitrogen (protein) content per unit leaf area. We hypothesize that alpine plants profit more from enhanced CO2 levels than lowland plants (Fig 7). Key-words: Microclimate, gas exchange, carboxylation, elevated CO2, nitrogen, anatomy, season, alpine


Oecologia | 1986

Altitudinal variation in stomatal conductance, nitrogen content and leaf anatomy in different plant life forms in New Zealand

Ch. Körner; Peter Bannister; Alan F. Mark

SummaryThis study is part of a series of investigations on the influence of altitude on structure and function of plant leaves. Unlike most other mountain areas, the Southern Alps of New Zealand provide localities where physiologically effective moisture stress occurs neither at high nor at low elevation, but the changes in temperature and radiation with elevation are similar or even steeper than in most other regions. In comparison with results from other mountains, where moisture may impair plant functioning at low elevation, this study allows an estimation of the relative role of water for the expression of various leaf features typically associated with alpine plants. Maximum leaf diffusive conductance (g), leaf nitrogen content (LN), stomatal density (n) and distribution, as well as area (A), thickness (d) and specific area (SLA) of leaves were studied. Three different plant life forms were investigated over their full altitudinal range (m): trees, represented by Nothofagus menziesii (1,200 m), ericaceous dwarf shrubs (1,700 m), and herbaceous plants of the genus Ranunculus (2,500 m). In all three life forms g, LN, and n increased, while SLA and A decreased with elevation. Recent investigations have found similar trends in other mountains from the temperate zone, but the changes are larger in New Zealand than elsewhere. Herbs show the greatest differences, followed by shrubs and then trees.It is concluded that g is dependent upon light climate rather than water supply, whereas SLA and related structural features appear to be controlled by the temperature regime, as they show similar altitudinal changes under different light and moisture gradients. The higher leaf nitrogen content found at high elevations in all three life forms, suggests that metabolic activity of mature leaves is not restricted by low nitrogen supply at high altitude. In general, the leaves of herbaceous plants show more pronounced structural and functional changes with altitude than the leaves of shrubs and trees.


Arctic, Antarctic, and Alpine Research | 2000

Tree growth near treeline : abrupt or gradual reduction with altitude?

Jens Paulsen; U. M. Weber; Ch. Körner

Natural climatic treelines are relatively discrete boundaries in the landscape established at a certain elevation within an otherwise continuous gradient of environmental change. By studying tree rings along elevational transects at and below the upper treeline in the European Alps, we (1) determine whether radial stem growth declines abruptly or gradually, and (2) test climatic influences on trees near treeline by investigating transects for climatically different historical periods. While tree height decreases gradually toward the treeline, there is no such general trend for radial tree growth. We found rather abrupt changes which imply threshold effects of temperature which moved upslope in a wave-like manner as temperatures increased over the past 150 yr. Currently radial tree growth at treeline in the Alps is the same magnitude as at several hundred meters below current treeline. Over short intervals, tree-ring width is more dependent on interannual climatic variability than on altitudinal distance to treeline. We conclude that (1) the elevational response of tree-rings includes a threshold component (a minimal seasonal temperature) and that (2) radial growth is more strongly correlated with year to year variation in climate than with treeline elevation as such. Our data indicate that the current treeline position reflects influences of past climates and not the current climate.


Oecologia | 1987

Dry matter partitioning and root length/leaf area ratios in herbaceous perennial plants with diverse altitudinal distribution

Ch. Körner; U. Renhardt

SummaryPartitioning patterns in 22 exclusively low and 27 exclusively high altitude perennial herbaceous species were examined in order to test the hypothesis that plants of high altitudes allocate more dry matter to below-ground parts and in particular to storage organs, than typical low altitude plants. Our results raise some doubts about the general validity of this hypothesis. The mean fractions of total dry matter allocated to green leaves (22±2% s.e. at low and 24±2% at high altitude) and special storage organs (28±4% at both altitudes) do not differ significantly among sites. The mean relative portions of total dry matter allocated to above-ground plant parts amount to 57±3% at low and 42±3% at high elevation (P=0.002) and differ less than often assumed. The greater below-ground fraction at high altitude results from reduced stem and proportionally increased fine root compartments. At high altitude specific root length is increased by 50% and mean individual rooting density is tripled. Fine root length per unit leaf area is 4.5 times greater (P<0.001). However, interspecific variation in all these quantities is considerable and species with quite contrasting partitioning patterns coexist at both elevations. This suggests that the success of perennial herbaceous plants at high elevations does not necessarily depend on a large below ground biomass fraction. The increased fine root length at high altitude may substitute for reduced mycorrhizal infection. Figure 1 provides a graphical summary.


Oecologia | 1998

Soil moisture dynamics of calcareous grassland under elevated CO2

Pascal A. Niklaus; D. Spinnler; Ch. Körner

Abstract Water relations of nutrient-poor calcareous grassland under long-term CO2 enrichment were investigated. Understanding CO2 effects on soil moisture is critical because productivity in these grasslands is water limited. In general, leaf conductance was reduced at elevated CO2, but responses strongly depended on date and species. Evapotranspiration (measured as H2O gas exchange) revealed only small, non-significant reductions at elevated CO2, indicating that leaf conductance effects were strongly buffered by leaf boundary layer and canopy conductance (leaf area index was not or only marginally increased under elevated CO2). However, these minute and non-significant responses of water vapour loss accumulated over time and resulted in significantly higher soil moisture in CO2-enriched plots (gravimetric spot measurements and continuous readings using a network of time-domain reflectometry probes). Differences strongly depended on date, with the smallest effects when soil moisture was very high (after heavy precipitation) and effects were largest at intermediate soil moisture. Elevated CO2 also affected diurnal soil moisture courses and rewetting of soils after precipitation. We conclude that ecosystem-level controls of the water balance (including soil feedbacks) overshadow by far the physiological effects observed at the leaf level. Indirect effects of CO2 enrichment mediated by trends in soil moisture will have far-ranging consequences on plant species composition, soil bacterial and faunal activity as well as on soil physical structure and may indirectly also affect hydrology and trace gas emissions and atmospheric chemistry.


Ecological Monographs | 2001

A long-term field study on biodiversity × elevated CO2 interactions in Grassland

Pascal A. Niklaus; P. W. Leadley; Bernhard Schmid; Ch. Körner

Interactive effects of increases in atmospheric CO2 and reductions in plant species diversity were investigated in planted calcareous grassland communities in northwestern Switzerland. The experimental communities were composed of 5, 12, and 31 species assembled from the native species pool. The study aimed at testing whether the CO2 responses of ecosystems change when specific sets of species are lost from plant communities. Species were selected so that the proportion of grasses, legumes, and non-legume forb individuals remained constant across levels of diversity. The most diverse plant community had approximately the same diversity as the surrounding grassland, and species occurring in less diverse communities were subsets of the species in the more diverse communities. The factorial atmospheric-CO2 treatment was applied using 50-cm-tall, open-bottom, open-top wind screens. Plant community-level responses and the responses of the individual species were assessed over a period of five years. A signific...


Oecologia | 1997

Will rising atmospheric CO2 affect leaf litter quality and in situ decomposition rates in native plant communities

G. Hirschel; Ch. Körner; J. A. Arnone Iii.

Abstract Though field data for naturally senesced leaf litter are rare, it is commonly assumed that rising atmospheric CO2 concentrations will reduce leaf litter quality and decomposition rates in terrestrial ecosystems and that this will lead to decreased rates of nutrient cycling and increased carbon sequestration in native ecosystems. We generally found that the quality of␣naturally senesced leaf litter (i.e. concentrations of C, N and lignin; C:N, lignin:N) of a variety of native plant species produced in alpine, temperate and tropical communities maintained at elevated CO2 (600–680 μl l−1) was not significantly different from that produced in similar communities maintained at current ambient CO2 concentrations (340–355 μl l−1). When this litter was allowed to decompose in situ in a humid tropical forest in Panama (Cecropia peltata, Elettaria cardamomum, and Ficus benjamina, 130 days exposure) and in a lowland temperate calcareous grassland in Switzerland (Carex flacca and a graminoid species mixture; 261 days exposure), decomposition rates of litter produced under ambient and elevated CO2 did not differ significantly. The one exception to this pattern occurred in the high alpine sedge, Carex curvula, growing in the Swiss Alps. Decomposition of litter produced in situ under elevated CO2 was significantly slower than that of litter produced under ambient CO2 (14% vs. 21% of the initial litter mass had decomposed over a 61-day exposure period, respectively). Overall, our results indicate that relatively little or no change in leaf litter quality can be expected in plant communities growing under soil fertilities common in many native ecosystems as atmospheric CO2 concentrations continue to rise. Even in situations where small reductions in litter quality do occur, these may not necessarily lead to significantly slower rates of decomposition. Hence in many native species in situ litter decomposition rates, and the time course of decomposition, may remain relatively unaffected by rising CO2.


Oecologia | 1985

Stomatal responses and water relations of Eucalyptus pauciflora in summer along an elevational gradient

Ch. Körner; P. M. Cochrane

SummaryThe spatial and temporal variation of lead conductance (g) in Eucalyptus pauciflora was analysed with respect to photon flux area density (I), temperature (T), water vapour concentration deficit (Δw), and leaf water potential (Ψ) at four different sites between 940 m and 2,040 m altitude in the Snowy Mountains of south-eastern Australia. Along this altitudinal gradient the precipitation/evaporation ratio increases from 1 to 4. The results show that gas diffusion in this tree species is primarily controlled by I and Δw at all sites, independently of the specific soil moisture regime. Even under dry midsummer conditions with predawn leaf water potentials of-1 MPa at the lowest altitude, Ψ had no striking effect on g.The humidity threshold for the onset of stomatal closure does not vary greatly between the study sites (12.2±1.3 Pa kPa-1). The highest and lowest values observed for Ψ, the osmotic potential at water saturation (from pressure/volume curves), the mean and maximum g and stomatal dentity, all increase with elevation. The highest (least negative) osmotic potentials were obtained at all sites in midsummer. It therefore appears that there is no osmotic adjustment to drought in the seasonal course. The maximum difference between osmotic potentials obtained at the lowest and highest sites is 0.46 MPa. In general osmotic potential varies less than has been reported for other plant species exposed to varying water regimes. This may be the consequence of the pronounced feed-forward response of the stomata to evaporative demand, which led to only moderate tissue desiccation, never exceeding the turgor loss point. E. pauciflora is a tree species with a very conservative utilisation of soil water, which adjusts to drought via stomatal control of water loss, rather than via osmotic properties.These results explain previous reports of the comparatively high susceptibility of E. pauciflora to severe drought and its positive influence on the hydrological balance of mountain ecosystems in the Australian Alps.

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Graham D. Farquhar

Australian National University

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