Abstract
Stable carbon and nitrogen isotope signals in plant tissues integrate plant-environment interactions over long periods. In this study, we hypothesized that humid alpine life conditions are narrowing the scope for significant deviations from common carbon, water and nitrogen relations as captured by stable isotope signals. We explored the variation in δ13C and δ15N in 32 plant species from tissue type to ecosystem scale across a suite of locations at c. Two thousand five hundred meter elevation in the Swiss Alps. Foliar δ13C and δ15N varied among species by about 3–4‰ and 7–8‰ respectively. However, there was no overall difference in means of δ13C and δ15N for species sampled in different plant communities or when bulk plant dry matter harvests of different plant communities were compared. δ13C was found to be highly species specific, so that the ranking among species was mostly maintained across 11 habitats. However, δ15N varied significantly from place to place in all species (a range of 2.7‰) except in Fabaceae (Trifolium alpinum) and Juncaceae (Luzula lutea). There was also a substantial variation among individuals of the same species collected next to each other. No difference was found in foliar δ15N of non-legumes, which were either collected next to or away from the most common legume, T. alpinum. δ15N data place Cyperaceae and Juncaceae, just like Fabaceae, in a low discrimination category, well separated from other families. Soil δ15N was higher than in plants and increased with soil depth. The results indicate a high functional diversity in alpine plants that is similar to that reported for low elevation plants. We conclude that the surprisingly high variation in δ13C and δ15N signals in the studied high elevation plants is largely species specific (genetic) and insensitive to obvious environmental cues.
Highlights
Based on the correlation between the discrimination of the heavy 13C isotope during CO2 gas exchange and habitat conditions, δ13C has become an important ecological index of plant carbon and water relations and photosynthesis performance (Dawson et al, 2002)
More recent broad samplings of congeneric species revealed that the reduced over all 13C discrimination with elevation is associated with atmospheric pressure and is not related to reduced temperature (Zhu et al, 2010; Zhou et al, 2011), matching results of earlier gas exchange works that showed that temperature exerts minor influences on carbon uptake in alpine plants (Körner, 1982; Körner and Diemer, 1987)
Intra-Plant (Tissue) Variation in δ13C and δ15N Overall, no statistically significant organ effect on δ13C was found in C. foetida (p = 0.26) and C. sempervirens (p = 0.48), some post hoc pairwise tests for individual organ types showed a difference in C. foetida (Figure 2)
Summary
Based on the correlation between the discrimination of the heavy 13C isotope during CO2 gas exchange and habitat conditions, δ13C has become an important ecological index of plant carbon and water relations and photosynthesis performance (Dawson et al, 2002). More recent broad samplings of congeneric species revealed that the reduced over all 13C discrimination with elevation is associated with atmospheric pressure (its various side effects) and is not related to reduced temperature (Zhu et al, 2010; Zhou et al, 2011), matching results of earlier gas exchange works that showed that temperature exerts minor influences on carbon uptake in alpine plants (Körner, 1982; Körner and Diemer, 1987) Seeming deviations from this pattern had been reported when elevational gradients were confounded with moisture gradients or when the elevational gradients explored were too narrow so that local peculiarities of soil conditions or in genotype overtopped the elevation signal (Körner, 2007). The influence of topography on the distribution of plant species (May and Webber, 1982), on the above-ground and belowground productivity (Billings and Bliss, 1959) and on nitrogen cycling (Fisk et al, 1998) have been well demonstrated in different alpine sites
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