Adaptation and plasticity in aboveground allometry variation of four pine species along environmental gradients

Abstract

Plant species aboveground allometry can be viewed as a functional trait that reflects the evolutionary tradeâ off between aboveâ and belowground resources. In forest trees, allometry is related to productivity and resilience in different environments, and it is tightly connected with a compromise between efficiencyâ safety and competitive ability. A better understanding on how this trait varies within and across species is critical to determine the potential of a species/population to perform along environmental gradients. We followed a hierarchical framework to assess tree heightâ diameter allometry variation within and across four common European Pinus species. Tree heightâ diameter allometry variation was a function of solely genetic components â approximated by either population effects or clinal geographic responses of the population’s site of originâ and differential genetic plastic responses â approximated by the interaction between populations and two climatic variables of the growing sites (temperature and precipitation)â . Our results suggest that, at the species level, climate of the growing sites set the tree heightâ diameter allometry of xeric and mesic species (Pinus halepensis, P. pinaster and P. nigra) apart from the boreal species (P. sylvestris), suggesting a weak signal of their phylogenies in the tree heightâ diameter allometry variation. Moreover, accounting for interpopulation variability within species for the four pine species aided to: (1) detect genetic differences among populations in allometry variation, which in P. nigra and P. pinaster were linked to gene pools â genetic diversity measurementsâ ; (2) reveal the presence of differential genetic variation in plastic responses along two climatic gradients in tree allometry variation. In P. sylvestris and P. nigra, genetic variation was the result of adaptive patterns to climate, while in P. pinaster and P. halepensis, this signal was either weaker or absent, respectively; and (3) detect local adaptation in the exponent of the tree heightâ diameter allometry relationship in two of the four species (P. sylvestris and P. nigra), as it was a function of populations’ latitude and altitude variables. Our findings suggest that the four species have been subjected to different historical and climatic constraints that might have driven their aboveground allometry and promoted different life strategies.We address the fate of four pine species to face, or already facing, a climate change context by accounting the intraspecific variation held within species. However, instead of using single traits, the novelty of the study lies in the use of a composite trait, specifically the aboveground allometry relationship, offering a more complete understanding of the species’s performance.