Tunicate bulb size variation in monocots explained by temperature and phenology

Functional and ecological diversification of underground organs in Solanum

The evolution of geophytes in response to different environmental stressors is poorly understood largely due to the great morphological variation in underground plant organs, which includes species with rhizomatous structures or underground storage organs (USOs). Here we compare the evolution and ecological niche patterns of different geophytic organs in Solanum L., classified based on a functional definition and using a clade-based approach with an expert-verified specimen occurrence dataset. Results from PERMANOVA and Phylogenetic ANOVAs indicate that geophytic species occupy drier areas, with rhizomatous species found in the hottest areas whereas species with USOs are restricted to cooler areas in the montane tropics. In addition, rhizomatous species appear to be adapted to fire-driven disturbance, in contrast to species with USOs that appear to be adapted to prolonged climatic disturbance such as unfavorable growing conditions due to drought and cold. We also show that the evolution of rhizome-like structures leads to changes in the relationship between range size and niche breadth. Ancestral state reconstruction shows that in Solanum rhizomatous species are evolutionarily more labile compared to species with USOs. Our results suggest that underground organs enable plants to shift their niches towards distinct extreme environmental conditions and have different evolutionary constraints.

Floral traits and reproductive success variation among inflorescence orders in Eryngium maritimum

Eryngium maritimum L. is considered a key species in dunes of the western Mediterranean. Although Northern European populations are endangered, the Mediterranean populations show a good conservation status, despite a lack of studies of the reproductive requirements and strategies of this species. This study aims to analyse the reproductive biology of a population of E. maritimum in the western Mediterranean (Balearic Islands, Spain), specifically focusing on differences in morphometric and reproductive traits among inflorescence orders. Capitulum size, number of flowers, fruit set and seed set were analysed to evaluate the morphological and reproductive differences among inflorescence orders. The association between subterranean development and investment in reproductive structures was also studied along the dune location. Breeding system was analysed, evaluating self-pollination capacity at capitulum level and the pollen/ovary ratio. Finally, floral visitors were assessed. Morphometric and reproductive traits showed a decline in size and production from early to subsequent inflorescence orders. A correlation between width of stem base (caudex) and number of reproductive structures was observed, whereas seashore distance did not affect the reproductive development. Flowering occurred during summer, from May until late July, while fructification took place from the middle of August until the last days of September. Pollinator exclusion treatments induced a fruit and seed set decline. Twenty-one species of floral visitor were found. First and second inflorescence orders contributed to the generation of seeds, displaying high fruit and seed production, while other inflorescence orders seemed to attract pollinators. Reproductive and non-reproductive development could depend on the capacity to reallocate resources from underground to aerial structures, which seemed to be superior in samples with highly developed caudices. In the studied population, inner areas closest to the seashore showed a delay in anthesis, which could be related to microclimate differences along the coast-to-inland gradient. Pollination is strongly entomophilous and showed low levels of self-compatibility at capitulum level. Considering these results, for habitat conservation the reported microclimate diversity should be taken into consideration, with a focus on conservation of the pollinator populations.

Get the shovel: morphological and evolutionary complexities of belowground organs in geophytes

Herbaceous plants collectively known as geophytes, which regrow from belowground buds, are distributed around the globe and throughout the land plant tree of life. The geophytic habit is an evolutionarily and ecologically important growth form in plants, permitting novel life history strategies, enabling the occupation of more seasonal climates, mediating interactions between plants and their water and nutrient resources, and influencing macroevolutionary patterns by enabling differential diversification and adaptation. These taxa are excellent study systems for understanding how convergence on a similar growth habit (i.e., geophytism) can occur via different morphological and developmental mechanisms. Despite the importance of belowground organs for characterizing whole-plant morphological diversity, the morphology and evolution of these organs have been vastly understudied with most research focusing on only a few crop systems. Here, we clarify the terminology commonly used (and sometimes misused) to describe geophytes and their underground organs and highlight key evolutionary patterns of the belowground morphology of geophytic plants. Additionally, we advocate for increasing resources for geophyte research and implementing standardized ontological definitions of geophytic organs to improve our understanding of the factors controlling, promoting, and maintaining geophyte diversity.

Do seedlings of larger geophytic species outperform smaller ones when challenged by drought?

PREMISE

In semiarid regions, decreasing rainfall presents a challenge to perennial seedlings that must reach sufficient size to survive the first year's seasonal drought. Attaining a large storage organ size has been hypothesized to enhance drought resilience in geophytes, but building larger storage organs requires faster growth, but paradoxically, some traits that confer faster growth are highly sensitive to drought. We examined whether tuber size confers greater drought resilience in seedlings of four closely related geophytic species of Pelargonium.

METHODS

We imposed two drought treatments when seedlings were 2 months old: chronic low water and acute water restriction for 10 days. Plants in the acute dry-down treatment were then rewatered at control levels. We compared morphological and ecophysiological traits at 2, 3, and 6 months of age and used mixed-effects models to identify traits determining tuber biomass at dormancy.

RESULTS

Despite a 10-fold variation in size, species had similar physiological trait values under well-watered conditions. Chronic and acute droughts negatively affected tuber size at the end of the season, but only in the two species with large tubers. Chronic drought did not affect physiological traits of any species, but in response to acute drought, larger species showed reduced photosynthetic performance. Canopy area was the best predictor of final tuber biomass.

CONCLUSIONS

Contradictory to the hypothesis that large tubers provide greater drought resiliency, small Pelargonium seedlings actually had higher drought tolerance, although at the expense of more vigorous growth compared to species with larger tubers under well-watered conditions.

Angiosperms at the edge: Extremity, diversity, and phylogeny

A hallmark of flowering plants is their ability to invade some of the most extreme and dynamic habitats, including cold and dry biomes, to a far greater extent than other land plants. Recent work has provided insight to the phylogenetic distribution and evolutionary mechanisms which have enabled this success, yet needed is a synthesis of evolutionary perspectives with plant physiological traits, morphology, and genomic diversity. Linking these disparate components will not only lead to better understand the evolutionary parallelism and diversification of plants with these two strategies, but also to provide the framework needed for directing future research. We summarize the primary physiological and structural traits involved in response to cold- and drought stress, outline the phylogenetic distribution of these adaptations, and describe the recurring association of these changes with rapid diversification events that occurred in multiple lineages over the past 15 million years. Across these threefold facets of dry-cold correlation (traits, phylogeny, and time) we stress the contrast between (a) the amazing diversity of solutions flowering plants have developed in the face of extreme environments and (b) a broad correlation between cold and dry adaptations that in some cases may hint at deep common origins.