The trait-based approach in plant ecology aims at understanding and classifying the diversity of ecological strategies by comparing plant morphology and physiology across organisms. The major drawback of the approach is that the time and financial cost of measuring the traits on many individuals and environments can be prohibitive. We show that combining near-infrared spectroscopy (NIRS) with deep learning resolves this limitation by quickly, non-destructively, and accurately measuring a suite of traits, including plant morphology, chemistry, and metabolism. Such an approach also allows to position plants within the well-known CSR triangle that depicts the diversity of plant ecological strategies. The processing of NIRS through deep learning identifies the effect of growth conditions on trait values, an issue that plagues traditional statistical approaches. Together, the coupling of NIRS and deep learning is a promising high-throughput approach to capture a range of ecological information on plant diversity and functioning and can accelerate the creation of extensive trait databases.

Background and Aims Determining within-species large-scale variation in phenotypic traits is central to elucidate the drivers of species’ ranges. Intraspecific comparisons offer the opportunity to understand how trade-offs and biogeographical history constrain adaptation to contrasted environmental conditions. Here we test whether functional traits, ecological strategies from the CSR scheme and phenotypic plasticity in response to abiotic stress vary along a latitudinal or a center- margins gradient within the native range of Arabidopsis thaliana. Methods We experimentally examined the phenotypic outcomes of plant adaptation at the center and margins of its geographic range using 30 accessions from southern, central and northern Europe. We characterized the variation of traits related to stress tolerance, resource use, colonization ability, CSR strategy scores, survival and fecundity in response to high temperature (34 °C) or frost (- 6 °C), combined with a water deficit treatment. Key Results We found evidence for both a latitudinal and a center-margins differentiation for the traits under scrutiny. Age at maturity, leaf dry matter content, specific leaf area and leaf nitrogen content varied along a latitudinal gradient. Northern accessions presented a greater survival to stress than central and southern accessions. Leaf area, C-scores, R-scores and fruit number followed a center-margins differentiation. Central accessions displayed a higher phenotypic plasticity than northern and southern accessions for most studied traits. Conclusions Traits related to an acquisitive/conservative resource-use trade-off followed a latitudinal gradient. Traits associated with a competition/colonization trade-off differentiated along the historic colonization of the distribution range and then followed a center-margins differentiation. Our findings pinpoint the need to consider the joint effect of evolutionary history and environmental factors when examining phenotypic variation across the distribution range of a species.

Background and Aims: Determining within-species large-scale variation in phenotypic traits is central to elucidate the drivers of species ranges. Intraspecific comparisons offer the opportunity to understand how trade-offs and biogeographical history constrain adaptation to contrasted environmental conditions. Here we test whether functional traits, ecological strategies and phenotypic plasticity in response to abiotic stress vary along a latitudinal or a center- margins gradient within the native range of Arabidopsis thaliana. Methods: The phenotypic outcomes of plant adaptation at the center and margins of its geographic range were experimentally examined in 30 accessions from southern, central and northern Europe. The variation of traits related to stress tolerance, resource use, colonization ability as well as survival and fecundity was determined in response to high temperature (34C) or frost (- 6C), in combination with response to water deficit. Key Results: Both evidence for a latitudinal and a center-margins differentiation was found. Traits related to the acquisitive/conservative strategy trade-off varied along a latitudinal gradient. Northern accessions presented a greater survival to stress than central and southern accessions. Traits related to a colonization-competition trade-off followed a center-margin differentiation. Central accessions presented a higher phenotypic plasticity and trait values associated with a higher colonization ability than northern and southern accessions which instead had a higher competition ability. Conclusions: Intraspecific phenotypic variation helps us understand how the distribution range has evolved in Arabidopsis thaliana, which is shaped both by climate and the population migratory history. We advocate to consider intraspecific trait variation in species range studies instead of species means only as classically done in macroecology.

How trade-offs between traits constrain adaptation to contrasted environments is critical to understand the distribution range of a given species. In Arabidopsis thaliana, genetic analyses recently revealed that a group of genotypes successfully recolonized Europe from its center after the last glaciation, outcompeting older lineages and leaving them only at the distribution margins, where environmental conditions are more stressing. However, whether trade-offs between traits related to dispersal, competition, and stress tolerance explain the success and persistence of different lineages across the species geographic range remains an open question. Here, we compared the genetic and phenotypic differentiation between 72 ecotypes originating from three geographical groups in Europe (North, South and Center). We measured key traits related to fecundity, dispersal ability, competition tolerance, and stress tolerance, and used genomic data to infer the effect of selection on these traits. We showed that a trade-off between plant fecundity and seed mass constrains the diversification of A. thaliana in Europe. In particular, the success of the cosmopolitan genotypes that recolonized Europe can be explained by their higher dispersal ability at the expense of their competitive ability and stress tolerance. Inversely, peripheral ecotypes exhibited the opposite trait syndrome: high competition and stress tolerance but low dispersal ability. Moreover, peripheral genotypes tend to differentiate from central ones at genes involved in dispersal and competitive traits such as seed mass. Combining ecological and genomic approaches, our study demonstrated the role of key ecological trade-offs as evolutionary drivers of the distribution of plant populations along a geographic gradient.

Plant-herbivore interactions mediated by plant-plant signaling were documented in different species. Here, we tested if herbivore foraging activity on plants was influenced by plant's prior contact with a damaged plant and if the effect of such plant-plant signaling was variable across genotypes. We filmed snails during one hour on two plants differing only in a prior contact with a damaged plant or not. We replicated eight times the experiment on 113 natural genotypes of Arabidopsis thaliana. We recorded snails' first choice, and measured its first duration on a plant, the proportion of time spent on both plants and leaf consumption. On average, snails spent more time on plants that experienced a prior contact with a damaged plant, and consumed them more. However, plant-plant signaling effect on snail behavior was variable across genotypes. Genome-wide association studies revealed that a small number of genetic polymorphisms related to stress coping ability and jasmonate pathway explained this variation. Plant-plant signaling modified the foraging activity of herbivores in A. thaliana. Depending on the plant genotype, plant-plant signaling made undamaged plants more repulsive or attractive to snails. This finding questions the theoretical basement of the evolution of plant-herbivore interactions mediated by plant-plant signaling.

Interactions between damaged plants and their neighbours are generally associated with increased levels of plant defence. This phenomenon appears widespread across biomes, growth forms and phylogeny (Karban, 2021;Karban et al., 2014). The effect of plant-plant signalling on plant-herbivore interactions is often considered adaptive, as it is expected to be naturally selected to reduce plant biomass loss, leading to increased individual fitness (Heil & Karban, 2010). However, the extent to which this process is genetically variable, which is a prerequisite for natural selection to act (Falconer et al., 1996), has hardly been examined so far.Plant-plant signalling can have prompt effects on herbivore foraging activity. Contact with a damaged plant can prime defences, which allows faster response in case of future herbivore attack