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Lianas and trees exhibit divergent intrinsic water-use efficiency along elevational gradients in South American and African tropical forests

Abstract:

Aim: Elevational gradients provide excellent opportunities to explore long-term morphological and physiological responses of plants to environmental change. We determined the difference in the elevational pattern of foliar carbon isotope composition (δ13C) between lianas and trees, and assessed whether this difference arises from changes in photosynthesis or stomatal conductance. We also explored the pattern of nutrient limitations with the elevation of these two growth forms. Location: The study was conducted in two mountain forests situated in the Neotropics and Palaeotropics. Time period: August–September 2015 and August–October 2016. Major taxa studied: Lianas and trees. Methods: We conducted inventories of lianas and trees using standardized techniques along elevational gradients in Ecuador and Rwanda. We determined the values of several foliar traits including δ13C and chemical traits in dominant liana and tree species. We set up Bayesian linear mixed-effect models to quantify the effects of elevation and growth form on each of the foliar traits, and the difference of the effect of elevation between the two growth forms (lianas and trees). Results: We found consistent growth form specific divergences in foliar δ13C and carbon to nitrogen ratio (C : N) responses to elevation. While we noted a meaningful increase in foliar δ13C and C : N with elevation for trees, lianas did not exhibit such a trend. Foliar δ13C and C : N remained relatively constant for lianas along the transects. Main conclusions: Lianas operate at relatively constant intrinsic water- and nitrogen-use efficiencies with elevation compared with trees. Altogether, the study suggests the existence of a functional divergence of water and nutrient use strategies between lianas and trees along tropical elevational transects.