Abstract
Leaf morphological traits vary along climate gradients, but it is currently unclear to what extent this results from acclimation rather than adaptation. Knowing so is important for predicting the functioning of long-lived organisms, such as trees, in a rapidly changing climate. We investigated the leaf morphological warming responses of 18 tropical tree species with early (ES) abd late (LS) successional strategies, planted at three sites along an elevation gradient from 2400 m a.s.l. (15.2 °C mean temperature) to 1300 m a.s.l. (20.6 °C mean temperature) in Rwanda. Leaf size expressed as leaf area (LA) and leaf mass per area (LMA) decreased, while leaf width-to-length ratio (W/L) increased with warming, but only for one third to half of the species. While LA decreased in ES species, but mostly not in LS species, changes in LMA and leaf W/L were common in both successional groups. ES species had lower LMA and higher LA and leaf W/L compared to LS species. Values of LMA and LA of juvenile trees in this study were mostly similar to corresponding data on four mature tree species in another elevation-gradient study in Rwanda, indicating that our results are applicable also to mature forest trees. We conclude that leaf morphological responses to warming differ greatly between both successional groups and individual species, with potential consequences for species competitiveness and community composition in a warmer climate.
Highlights
While it is well known that leaf traits are adapted to the environment where the species occur, the possibility to acclimate these traits to altered environmental conditions is crucial to the success with which plants and their ecosystems will respond to climate change [7,8,9]
ES species had significantly higher leaf width-to-length ratio (W/L) ratio, leaf area (LA), NM and PM, and lower leaf mass per unit area (LMA) and leaf density (LD) compared to the LS species
The overall similarity between the responses from young and mature trees provides support for using more frequently available data from young trees to predict climate change effects on leaf morphology of mature forest trees, but with caution, as the responses are very species-specific. This elevation-gradient study demonstrated that effects of a warmer climate on leaf morphology are highly variable among species, and sometimes between successional groups
Summary
Structural, chemical and physiological leaf traits have a decisive influence on the productivity of plants and their ecosystems [1,2]. Leaf morphological traits, such as leaf mass per unit area (LMA), leaf size and shape, influence the interception of light and the exchange of gases and energy between plants and the atmosphere, thereby controlling plant photosynthesis, transpiration and leaf temperature [3,4,5,6]. While it is well known that leaf traits are adapted to the environment where the species occur, the possibility to acclimate these traits to altered environmental conditions is crucial to the success with which plants and their ecosystems will respond to climate change [7,8,9]. LMA responds to environmental factors, such as light, temperature, water and nutrient availability [15,16]
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