Volume 13, Issue 6, December 2021

Several ecological and genetic processes acting in concert account for population differentiation, which is a pervasive process in nature that may eventually lead to speciation. In this special issue, we gathered a collection of papers dealing with various ecological and genetic aspects of population differentiation in plants covering a wide array of worldwide environments, plant functional types, genetic and genomic approaches, and common garden experiments to quantify molecular and/or quantitative trait differentiation in plant populations.

Applications of restoration practices in wetland systems frequently must contend with plant invasion by non-targeted species, and these invading plants can undermine restoration goals through impacts both above- and below-ground. In this study we examined the impacts of invasive plants among natural and created vernal pools in California and found that invasion had a large effect on the plants present in the community and especially influenced plant litter decomposition rates. These invasive species caused changes can have implications for long-term alterations in plant-based inputs to soils; however, we did not detect associated shifts in below-ground function associated with invasion by non-native plants.

Pollinator-mediated interactions among co-flowering plants can result in positive (facilitation), negative (competition) or neutral outcomes for plants. Despite their importance in plant community assembly, experimental assessment of the bidirectional effects of pollinator-mediated interactions is still limited. Based on evaluation of pollen transfer dynamics (conspecific and heterospecific pollen deposition) and plant reproductive success of co-flowering Mimulus guttatus and Delphinium uliginosum, we show asymmetrical pollinator-mediated effects which were dependent on geographical location. Our results show that competition and facilitation can act simultaneously between co-flowering species and provide evidence of a spatial mosaic of pollinator-mediated interactions.

Tamarix ramosissima seeds were extremely small and possessed radial pappus on one end. The seed pappus of T. ramosissima had no significant effect on seed germination but may provide a buoyancy force that aids the long-distance dispersal of seeds. In addition, we found that the hypocotyl hairs may help the early seedlings become fixed to the surface matrix and provide support to the seedling before the appearance of roots; such a structure might have evolved to facilitate seed dispersal and seedling establishment during flooding and floating water conditions.

Wood anatomical traits reflect the adaptations along an aridity gradient in oak species. We found that high temperatures combined with periodic water deficits lead to narrower vessels, high-density wood occupied by smaller fibres. On the contrary, on humid sites, tall oaks invest in widest vessels to conduct water with great efficiency. Oak species in the study site showed an adaptive response of wood traits to climate, but there is also evidence of a low phylogenetic signal. Co-occurrence of oak species with different leaf habits and phylogenetic trajectories may promote complementary resource acquisition.

We examined the mating system’s response to fire in Polygala lewtonii, a species endemic to fire-prone Florida sandhill and scrub. Polygala lewtonii has three flower types: above-ground chasmogamous (open-pollinated) and cleistogamous (closed, obligately self-fertilizing) flowers and below-ground cleistogamous flowers, with fruits produced both above-ground and below-ground. We used a genetic approach to test whether post-fire recolonization was accomplished primarily through germination of above-ground or below-ground seed. The below-ground selfed seeds showed an increased contribution to the population and new alleles emerged from the seed bank post-fire. These results suggest that amphicarpy is an adaptation to promote rapid post-fire colonization and preserve genetic variation and adaptive potential.

As the largest plateau in the world, the Qinghai–Tibet Plateau (QTP) is a hotspot for manyphylogeographic studies, but little is known about herbaceous plants. Here, we revealed the population genetic structure and two possible refuges of Iris loczyi distributed in QTP based on chloroplast DNA and microsatellite markers. The geographic isolation caused by multiple mountain ranges was contributed to the current distribution pattern of this species. Our findings provided new insights into the location of glacial refuges for the species distributed in QTP, and supplemented more species data for the response of QTP species to the Quaternary climate.

Our study comprehensively documents the morphological variation of trichomes (plant hairs) on both adaxial and abaxial surface of 14 Solanum species (mixture of wild and cultivated species), thus providing a catalogue of major trichome types in Solanum genus. For each trichome type, the detailed characterization, nomenclature, density on leaf surface (per mm² of leaf surface), dimensions (in µm) and a line art (visual tool) have been provided, which can act as an updated data source and reference tool for future studies.

When plants experience stressful environmental conditions, such as heat waves, this can even affect their offspring, a phenomenon called ‘transgenerational effects’. We were interested in how important the precise temporal patterns of heat stress are, and we therefore subjected Arabidopsis thaliana plants to a range of different heat stress regimes. We find that the timing of heat events is much more important than their frequency. We also find that the transgenerational responses of plants to heat are related to their climates of origin, which means they can evolve, and have probably already done so in the past.

Pollen deposition and plant resources (such as nutrient or water availability) limit seed production, yet interactions among these factors have rarely been considered. Using the California native plant, Phacelia parryi, scientists showed how the relationship between pollen deposition and seed production is altered by drought. This effect of drought changed the pollen range within which additional pollen deposition increased seed production. They then describe how changes in this pollen-to-seed relationship could be used to know when plants are expected to be pollen-limited, when drought affects pollinator effectiveness, and the impacts of abiotic conditions on seed production.

RhizoVision Explorer is a new, easy-to-use software that measures root traits like length, diameter, area and volume from images. The software is free and open-source so that future improvements are possible. RhizoVision Explorer was validated using a new and freely available image set containing different sizes of measured copper wires. The software is intended to democratize access to root biology and to be the standard for validated measurements.