Inter- and intraspecific variation in stomatal pore area index along elevational gradients and its relation to leaf functional traits
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Stomata are mediators of gas exchange and thus important for photosynthesis and plant performance. The aim of this study was to analyze the ecological explanatory power of the stomatal pore area index (SPI) calculated via stomatal size and density. We studied the SPI on sun leaves of 22 herbaceous species on 22 study sites being distributed along two elevational gradients in the northern Alps ranging from 700 to 1800 m a.s.l.. We analyzed its correlation with other functional traits related to plant performance namely specific leaf area (SLA), area-based leaf nitrogen and carbon (N area and C area, respectively) as well as carbon discrimination Δ13C within as well as between species. On a subset of four species we also measured light-saturated net photosynthetic rate at ambient CO2 concentration (A sat) and stomatal conductance on all sites. We found that SPI was positively correlated with A sat, yet the relation was weaker than expected. The reaction of SPI along the elevational gradients was highly species-specific and related to variations in other investigated leaf traits. The relationship with functional traits, however, differed between the inter- and intraspecific level in strength and direction. SPI was positively related to N area and C area and negatively with SLA and Δ13C for most species. However, we found no significant relation considering species mean values for Δ13C and N area. The relation of SPI to SLA was the most consistent displaying no difference when comparing the relation between and within species. This research shows that different processes may act on different organizational levels leading to the detected differences in trait–trait correlations on the inter- and intraspecific levels. It may have important consequences also for macroecological and modelling studies.
KeywordsStomatal pore area index (SPI) Potential conductance index (PCI) Plant functional traits Stomata Δ13C Altitude
The authors would like to thank the members of the Institute of Botany at the University of Regensburg, especially Patrizia König, Nina Berndt, Désirée Dotter, Melanie Hahn, Günther Kolb, Stefanie Meier, Sabine Moll, Sergey Rosbakh and Jessica Rossow for practical assistance and valuable discussions. We would also like to thank Thijs Pons and Manfred Küppers as well as two anonymous reviewers for valuable advice and comments on the manuscript. Rudi Schäufele at Technische Universität München in Freising carried out the isotope measurements. This work was supported by the Eliteförderung des Landes Bayern via provision of a scholarship (granted to SFB) and the University of Regensburg. We also acknowledge support from the Bavarian State Forest Enterprise and the district government of upper Bavaria. CR acknowledges financial support of the DFG (RO3842/3-1) and the DFG-Research Centre for integrative Biodiversity Research (iDiv).
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