Factors affecting cork oak growth under dry conditions: local adaptation and contrasting additive genetic variance within populations

Abstract

Increased drought severity is expected in the Mediterranean Basin over the twenty-first century, but our understanding of the potential of most forest tree species to cope with it remains uncertain. In this study, (1) we examined the potential effects of long-term selection and the capacity to respond to future changes in selective pressures in three populations of cork oak (Quercus suber L.). For this purpose, we evaluated the response to dry conditions of 45 open-pollinated trees originating from populations in Morocco, Portugal, and Spain. Growth, leaf size, specific leaf area (SLA), carbon isotope discrimination (Δ 13 C), leaf nitrogen content (N mass ), and total chlorophyll content (Chl mass ) were measured in 9-year-old plants. (2) We also investigated the relationships between functional traits and aboveground growth by regression models. Plants presenting larger and more sclerophyllous leaves (low SLA and high leaf thickness) exhibited higher growths, with results suggesting that these traits are subjected to divergent selection in this species. Heritability estimates were moderately high for Δ 13 C (0.43±0.25-0.83±0.31) and stem diameter (0.40±0.15-0.71±0.28) for the tree populations. For the rest of the traits (except for annual growth), heritability values varied among populations, particularly for height, leaf size, leaf thickness, and N mass . Our results suggest that natural selection has led to local adaptations and has also affected the genetic variance intrapopulation in these cork oak populations, although studies with a higher number of populations should be carried out across different years. Additionally, the absence of significant genetic correlations and the fact that correlated traits did not undergo opposing selection provided little evidence for constraints on evolution caused by genetic correlations.

Functional traits and adaptive capacity of European forests to climate change

“…Measurements of leaf traits (LS; SLA; δ 13 C; N mass ) adaptation in response to diverging climates Inter-population differences in LS, SLA and δ 13 C and a significant genotypeenvironment interaction for shoot growth were found.. Phenotypic correlation between the differences in shoot growth among years and the annual mean temperature is described.. Valiente et al, 2011 Common garden experiment with 3 populations (Morocco, Portugal, Spain) of 9-year-old plants.…”

Understanding the importance of intrapopulation functional variability and phenotypic plasticity in Quercus suber

“…Two plants per family were set in each block. Populations originated from sites in Morocco, Spain, and Portugal that have similar annual rainfall, but contrasting severity of the dry season (Ramirez-Valiente et al 2011). Briefly, there is a pattern of increasing drought severity and length toward southern sites.…”

Contrasting holm oak provenances show different field performance but similar resilience to drought events eight years after planting in a Mediterranean environment

“…Indeed, Gimeno et al (2008) pointed out that plasticity in this species is more important than adaptation and genetic differences among population in response to environmental stress. However, other studies have found a higher drought tolerance and lower SLA in Q. ilex and Q. suber seedlings from drier provenances , Ramírez-Valiente et al 2011. During the studied period, the most intense drought event occurred in 2012.…”

“…Ramírez-Valiente et al (2011) found that Q. suber populations from drier sites showed a higher growth potential. Several studies with other broadleaved tree species have also reported greater growth rates in those individuals from drier provenances (Savva et al 2007, Leland et al 2016.…”