Abstract
Large old trees are extraordinary organisms. They not only represent a historical, landscape and environmental heritage of inestimable value, but they also witness a long history of environmental changes and human interventions, and constitute an as yet poorly known reserve of genetic variability which can be considered a great resource for management programs of forest species. This is the first genetic study on Italian, large, old chestnut trees (Castanea sativa Mill.). Ninety-nine trees were surveyed and analysed. For each tree, more than one sample from canopy and root suckers was collected to test for the genetic integrity of the individuals. All samples were genotyped using nine nuclear microsatellite markers (nSSRs) and 106 unique genetic profiles were identified. A Bayesian analysis performed with the software STRUCTURE revealed the occurrence of two main gene pools and unveiled the genetic relationships existing among the genotyped individuals, and with the natural chestnut populations living in proximity. A phylogeographic structure of the plastid diversity was also obtained by the use of DNA sequence variation at two marker regions, revealing different origins and probable connections of the old trees with different glacial refugia. Our results contribute to an improved evaluation of the European chestnut genetic resources and provide useful insights into the species’ history and domestication in Italy. The importance of carefully targeted conservation strategies for these invaluable organisms is reaffirmed.
Highlights
Forests play a key ecological role in a myriad of flora and fauna terrestrial communities, representing a significant resource of biodiversity in terms of species and habitats, and providing a long list of ecosystem, socio-economic, and cultural services [1]
It appears of great importance to search, inventory, and evaluate the genetic identity of large old chestnuts across the species range, in order to preserve the capacity of adaptation and long-term survival to climate change, human pressure and new pests of its natural, naturalized, and cultivated stands
We based our survey on the Italian National Catalog of Monumental Trees, but we were able to recover a larger and perhaps unexpected number of plants with extraordinary dimensions
Summary
Forests play a key ecological role in a myriad of flora and fauna terrestrial communities, representing a significant resource of biodiversity in terms of species and habitats, and providing a long list of ecosystem, socio-economic, and cultural services [1]. Forests 2020, 11, 1118 ecophysiological characterization studies to identify endangered populations and species, to evaluate adaptive potential, and to define management strategies for their future conservation [6,7] In this context, large old trees are keystone ecological components and habitat to a large variety of organisms, thereby contributing to maintain high levels of forest biodiversity and resilience [8,9]. Recovering, preserving and studying these extraordinary individuals is important for the sense of beauty, wonder and memories they convey (i.e., a concept of “monumentality”), or for their well-known historical, cultural, and social values [10], and because they feature and drive stand structure, function and evolution across forest biomes [1,11] They represent a valuable and unique source of genetic diversity, which can testify distant evolutionary prints, peculiar abilities to cope with environmental changes and/or advantageous productivity traits [9,12,13]. The genetic characterization of these trees can be crucial to improve our knowledge on the molecular basis of local adaptation, identify selective drivers from different local and temporal forest settings, and contribute to explain the contemporary genetic variation of tree species
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