Variance of light-related leaf traits across spatial and temporal scales in the Mediterranean evergreen Olea europaea L.

Abstract

The variability in space and time of a given set of traits can describe the biological activity of plants and influence species interactions and the properties of communities and ecosystems. However, seasonal variance in foliar traits of tree species has been poorly addressed in the Mediterranean climate despite its potential implications in fundamental processes such as light interception strategies. Due to seasonal variation in the apparent sun path’s trajectory, predictable radiation patterns across crown positions may determine the variance partitioning for light-related leaf traits in evergreens. We hypothesize that in the most exposed part of the crown i.e. south, trait variance should be constraint due to abiotic stress compared to less exposed crown positions. We partitioned the variance across five nested scales for a set of traits that capture leaf form, structure, position relative to the sun and the potential area exposed in a given time in Olea europaea L. trees. The scales included temporal variation due to sampling in two different seasons and twelve spatially structured crown positions within trees. We conducted multivariate analyses to assess the variability among traits, within trees and among trees The variance partitioning at the season scale was low and the structure conserved between seasons for most traits. Intraindividual variance was conspicuous for all traits evidencing a spatial gradient of trait distribution within trees from outer to inner layers and among paired crown sectors (North-East, South-West). Leaf angles and potential exposure to direct light had an absence of variance at scales above crown positions. The spatial distribution of crown sectors and layers had a distinct influence on the expression of leaf attributes among traits. Environmental filters may constrain variability on the outermost layer of the crown and on all crown positions during summer and winter, due to combination of the high irradiance and water stress in Mediterranean climates.