Intraspecific responses to climate reveal nonintuitive warming impacts on a widespread thermophilic conifer.

Many ecologically important forest trees from dry areas have been insufficiently investigated for their ability to adapt to the challenges posed by climate change, which hampers the implementation of mitigation policies. We analyzed 14 common-garden experiments across the Mediterranean which studied the widespread thermophilic conifer Pinus halepensis and involved 157 populations categorized into five ecotypes. Ecotype-specific tree height responses to climate were applied to projected climate change (2071-2100 ad), to project potential growth patterns both locally and across the species' range. We found contrasting ecotypic sensitivities to annual precipitation but comparatively uniform responses to mean temperature, while evidence of local adaptation for tree height was limited to mesic ecotypes. We projected intriguing patterns of response range-wide, implying either height inhibition or stimulation of up to 75%, and deduced that the ecotype currently experiencing more favorable (wetter) conditions will show the largest inhibition. Extensive height reductions can be expected for coastal areas of France, Greece, Spain and northern Africa. Our findings underline the fact that intraspecific variations in sensitivity to precipitation must be considered when projecting tree height responses of dry forests to future climate. The ecotype-specific projected performances call for management activities to ensure forest resilience in the Mediterranean through, for example, tailored deployment strategies.

How Do Cold-Adapted Plants Respond to Climatic Cycles? Interglacial Expansion Explains Current Distribution and Genomic Diversity in Primula farinosa L.

Understanding the effects of past climatic fluctuations on the distribution and population-size dynamics of cold-adapted species is essential for predicting their responses to ongoing global climate change. In spite of the heterogeneity of cold-adapted species, two main contrasting hypotheses have been proposed to explain their responses to Late Quaternary glacial cycles, namely, the interglacial contraction versus the interglacial expansion hypotheses. Here, we use the cold-adapted plant Primula farinosa to test two demographic models under each of the two alternative hypotheses and a fifth, null model. We first approximate the time and extent of demographic contractions and expansions during the Late Quaternary by projecting species distribution models across the last 72 ka. We also generate genome-wide sequence data using a Reduced Representation Library approach to reconstruct the spatial structure, genetic diversity, and phylogenetic relationships of lineages within P. farinosa. Finally, by integrating the results of climatic and genomic analyses in an Approximate Bayesian Computation framework, we propose the most likely model for the extent and direction of population-size changes in $P$. farinosa through the Late Quaternary. Our results support the interglacial expansion of $P$. farinosa, differing from the prevailing paradigm that the observed distribution of cold-adapted species currently fragmented in high altitude and latitude regions reflects the consequences of postglacial contraction processes.

Establishing the A. E. Watkins landrace cultivar collection as a resource for systematic gene discovery in bread wheat.

KEY MESSAGE: A high level of genetic diversity was found in the A. E. Watkins bread wheat landrace collection. Genotypic information was used to determine the population structure and to develop germplasm resources. In the 1930s A. E. Watkins acquired landrace cultivars of bread wheat (Triticum aestivum L.) from official channels of the board of Trade in London, many of which originated from local markets in 32 countries. The geographic distribution of the 826 landrace cultivars of the current collection, here called the Watkins collection, covers many Asian and European countries and some from Africa. The cultivars were genotyped with 41 microsatellite markers in order to investigate the genetic diversity and population structure of the collection. A high level of genetic diversity was found, higher than in a collection of modern European winter bread wheat varieties from 1945 to 2000. Furthermore, although weak, the population structure of the Watkins collection reveals nine ancestral geographical groupings. An exchange of genetic material between ancestral groups before commercial wheat-breeding started would be a possible explanation for this. The increased knowledge regarding the diversity of the Watkins collection was used to develop resources for wheat research and breeding, one of them a core set, which captures the majority of the genetic diversity detected. The understanding of genetic diversity and population structure together with the availability of breeding resources should help to accelerate the detection of new alleles in the Watkins collection.

Topo-climatic microrefugia explain the persistence of a rare endemic plant in the Alps during the last 21 millennia.

Ongoing rapid climate change is predicted to cause local extinction of plant species in mountain regions. However, some plant species could have persisted during Quaternary climate oscillations without shifting their range, despite the limited evidence from fossils. Here, we tested two candidate mechanisms of persistence by comparing the macrorefugia and microrefugia (MR) hypotheses. We used the rare and endemic Saxifraga florulenta as a model taxon and combined ensembles of species distribution models (SDMs) with a high-resolution paleoclimatic and topographic dataset to reconstruct its potential current and past distribution since the last glacial maximum. To test the macrorefugia hypothesis, we verified whether the species could have persisted in or shifted to geographic areas defined by its realized niche. We then identified potential MR based on climatic and topographic properties of the landscape and applied refined scenarios of MR dynamics and functions over time. Last, we quantified the number of known occurrences that could be explained by either the macrorefugia or MR model. A consensus of two or three SDM techniques predicted absence between 14-10, 3-4 and 1 ka bp, which did not support the macrorefugia model. In contrast, we showed that S. florulenta could have contracted into MR during periods of absence predicted by the SDMs and later re-colonized suitable areas according to the macrorefugia model. Assuming a limited and realistic seed dispersal distance for our species, we explained a large number of the current occurrences (61-96%). Additionally, we showed that MR could have facilitated range expansions or shifts of S. florulenta. Finally, we found that the most recent and the most stable MR were the ones closest to current occurrences. Hence, we propose a novel paradigm to explain plant persistence by highlighting the importance of supporting functions of MR when forecasting the fate of plant species under climate change.