Trait evolution in tropical rubber (Hevea brasiliensis) trees is related to dry season intensity

Abstract

Drought shapes the distribution and survival of trees even in tropical wet forests, and the wood and leaf trait spectra are used to understand drought adaptations. However, trait variation may result from ontogenetic adjustment or be related to tree size and not reflect evolutionary adaptations. Intraspecific variation in adaptations to drought can be an important factor in a species’ distribution and response to climate change, but excluding potentially confounding factors and proving adaptive evolution are challenging. Provenance trials can identify hereditary variability. We analysed wood and leaf traits in rubber (Hevea brasiliensis) tree clones from 15 locations in the Amazon basin that were planted in northern Thailand, controlled for tree size, tested for genetic relatedness and the phylogenetic signal in traits and compared trait variations with the climate at the location of origin. Correlations between traits and tree size were low. Intraspecific trait variation was similar to relationships in published among‐species comparisons, and correlations among wood traits and correlations among leaf traits were stronger than between wood and leaf traits. Genotype explained 30%–70% of the trait variation, and traits differed in how much of this variation was controlled by location or the relatedness among clones. There was no correlation with mean temperature or total annual rainfall. However, rainfall in the driest quarter (19–199 mm) was strongly related to leaf mass per area, carbon isotopic composition and area‐based nitrogen content (r2 = 0.54–0.70) and weaker to wood traits (vessel density and vessel lumen fraction). Trees from locations with a stronger dry season also had higher growth rates in Thailand. All traits correlating with climate showed a significant phylogenetic signal. We found no evidence of increased drought tolerance, but the trait spectrum and higher growth in trees from drier locations suggest that deciduous rubber trees have adapted via drought avoidance rather than tolerance. Our study also underlines the importance of looking at a suite of traits rather than individual ones to understand adaptive strategies. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13203/suppinfo is available for this article.

Influence of Cambial Age and Axial Height on the Spatial Patterns of Xylem Traits in Catalpa bungei, a Ring-Porous Tree Species Native to China

“…Negative effects of cambial age and axial height on annual diameter growth might be attributed to the developmental stages of studied trees, which are in later juvenile stages heading towards maturing stages. Weak correlations between wood anatomical traits agreed with previous work [73]. However, a strong relationship between vessel lumen diameter and vessel density was reported in other studies [74,75], which was not observed in this study.…”

Assessing adaptive and plastic responses in growth and functional traits in a 10‐year‐old common garden experiment with pedunculate oak (Quercus robur L.) suggests that directional selection can drive climatic adaptation

“…Higher SHM values indicate drier climatic conditions. We used different climatic variables for assessing intra‐specific differences in growth (MAT) and in functional traits (SHM) in order to account for the fact that genecological differences in tree growth in many earlier studies were best explained by the average temperature regime (e.g., Wang, O'Neill, & Aitken, 2010; Jobbágy & Jackson 2000; Loehle, 1998), whereas adaptive differences in functional traits with importance for drought adaptation were best explained by climate variables indicating probability of drought occurrence (e.g., Lamy et al., 2014; Rungwattana et al., 2018). We calculated a linear model between the functional trait value at provenance level and the climatic variables at seed origin and reported slopes and p‐values separately for the three test sites.…”

Beyond MAP: A guide to dimensions of rainfall variability for tropical ecology

“…Although tropical ecologists have often defaulted to using annual means to characterize rainfall regimes, a growing number of examples demonstrates that other dimensions of rainfall are either stronger predictors of spatial and temporal variation in ecological properties and processes than MAP, or that these dimensions can add substantial explanatory power after controlling for MAP (e.g., Davidar, Puyravaud, & Leigh, 2005;Ouédraogo et al, 2016;Parolari et al, 2019;Rungwattana et al, 2018;Tedesco et al, 2008;Williams & Middleton, 2008 Harris, Jones, Osborn, & Lister, 2014) and the National Oceanic and Atmospheric Administration (https://www.esrl.noaa.gov/psd/data/gridd ed/). Monthly, daily, or even hourly time series for locations of interest can be extracted from these datasets in a straightforward manner.…”