Annals of botany最新文献

Background and aims: Genomic changes triggered by polyploidy, chromosomal rearrangements, and/ or environmental stress are among factors that affect the activity of mobile elements, particularly Long Terminal Repeats Retrotransposons (LTR-RTs) and DNA transposons. Because these elements can proliferate and move throughout host genomes, altering the genetic, epigenetic and nucleotypic landscape, they have been recognized as a relevant evolutionary force. Beaksedges (Rhynchospora) stand out for their wide cosmopolitan distribution, high diversity (~400 spp.) and holocentric chromosomes related to high karyotypic diversity and a centromere-specific satDNA Tyba. This makes the genus an interesting model to investigate the interactions between repetitive elements, phylogenetic relationships, and ecological variables.

Methods: Here, we used comparative phylogenetic methods to investigate the forces driving the evolution of the entire set of mobile elements (mobilome) in the holocentric genus Rhynchospora. We statistically tested the impact of phylogenetic relationships, abundance of holocentromeric satDNA Tyba, diversity of repeatome composition, ecological variables, and chromosome number in mobile element diversification.

Key results: Tyba abundance was found to be inversely correlated with LTR-RT content. Decrease of LTR abundance and diversity was also related to increase in chromosome number (likely due to fission events), and colonization of dry environments in the northern hemisphere. In contrast, we found constant LTR insertions throughout time in species with lower chromosome numbers in rainier environments in South America. A multivariate model showed that different traits drive LTR abundance, especially repeat diversity and Tyba abundance. Other mobile elements, such as non-LTR RTs and DNA transposons had insufficient abundance to be included in our models.

Conclusions: Our findings suggest that LTR evolution is strongly impacted by the holocentric characteristics of Rhynchospora chromosomes, correlating with species diversification and biome shifts, and supporting a holokinetic drive model of evolution and a competitive scenario with Tyba. Altogether, our results present evidence of multi-trait influence on LTR-RT dynamics and provide a broader understanding of TE evolution in a macroevolutionary context.

Background and aims: To better understand C4 evolution in monocots, we characterized C3-C4 intermediate phenotypes in the grass genus Homolepis (subtribe Arthropogoninae).

Methods: Carbon isotope ratio (δ13C), leaf gas exchange, mesophyll (M) to bundle sheath (BS) tissue characteristics, organelle size and numbers in M and BS tissue, and tissue distribution of the P-subunit of glycine decarboxylase (GLDP) were determined for five Homolepis species and the C4 grass Mesosetum loliiforme from a phylogenetic sister clade. We generated a transcriptome-based phylogeny for Homolepis and Mesosetum species to interpret physiological and anatomical patterns in an evolutionary context, and to test for hybridization.

Key results: Homolepis contains two C3 (H. glutinosa, H. villaricensis), one weaker form of C2 termed sub-C2 (H. isocalycia), and two C2 species (H. longispicula, H. aturensis). Homolepis longispicula and H. aturensis express over 85% of leaf GDC in centripetal mitochondria within the BS, and have increased fractions of leaf chloroplasts, mitochondria and peroxisomes within the BS relative to H. glutinosa. Analysis of leaf gas exchange, cell ultrastructural, and transcript expression show M. loliiforme is a C4 plant of the NADP-malic enzyme subtype. Homolepis is comprised of two sister clades, one containing H. glutinosa and H. villaricensis and the second H. longispicula and H. aturensis. Homolepis isocalycia is of hybrid origin, with parents being H. aturensis and a common ancestor of the C3  Homolepis clade and H. longispicula.

Conclusions: Photosynthetic activation of BS tissue in the sub-C2 and C2 species of Homolepis is similar to patterns observed in C3-C4 intermediate eudicots, indicating common evolutionary pathways from C3 to C4 photosynthesis in these disparate clades. Hybridization can diversify the C3-C4 intermediate character state and should be considered in reconstructing putative ancestral states using phylogenetic analyses.

Background and aims: Nolana mollis is a dominant plant species in the hyperarid Atacama Desert. A previous hypothesis states that N. mollis owes its success to the condensation of atmospheric water from undersaturated air onto its leaf surfaces by exuded salts, and absorption of this water by its leaves, or by shallow roots following drip onto the soil surface; living roots of N. mollis were suggested to only exist near the soil surface.

Methods: We conducted a field experiment with three treatments to establish the source of N. mollis's water: control, root cutting to block uptake of all soil moisture, and plastic skirting at the soil surface to block leaf drip of atmospheric water.

Key results: Xylem tensions monotonically increased after root cutting until the plants wilted irreversibly, diverging clearly from the skirted and control treatments showing diurnal patterns of increasing tension in the day followed by recovery overnight.

Conclusions: Hydration in N. mollis requires access to deep soil water, motivating an alternative hypothesis: imperfect salt exclusion at the root surface and salt exudation by the leaf results in less root fouling and lower xylem tensions, while during the day evaporation of the surface brine, condensed overnight, increases the water use efficiency of carbon gain.

Background and aims: The absence of a modern plant-based 'dicotyledon' phytolith reference baseline impedes the accurate interpretation of fossil phytolith records in archaeological and palaeoecological research within North-western Europe. This study aims to fill this gap by documenting and analysing the phytolith record from modern dicotyledon taxa occurring in this region.

Methods: Phytoliths were extracted from several plant parts of 117 plant specimens representing 74 species (1-2 specimens/species). The study employed light microscopy to examine phytolith production (non-producer, trace, common, or abundant) and phytolith assemblage composition. The data were analysed statistically to (a) determine the influence of taxonomy and plant part on phytolith presence (absent/present) using a Mixed Model, (b) assess phytolith assemblage variation using a Permutational Multivariate Analysis of Variance (PerMANOVA), and (c) identify patterns among sample groups including segregation for plant part, life form (forbs vs shrubs/trees), and order using a Linear Discriminant Analyses (LDA).

Key results: Morphotype analysis reveals diagnostic morphotypes and features for specific plant families, genera, and plant parts. LDA effectively segregated plant parts and life forms, though taxonomic groupings showed limited segregation. Phytolith presence (absent/present) was found to vary, influenced by both plant part and taxonomy. For species examined through two specimens, although phytolith production varied considerably, phytolith assemblage composition was consistent.

Conclusions: This study establishes a 'dicotyledon' phytolith baseline for North-western Europe, showing that the phytolith record can be informative in terms of plant part and life form and that several phytolith morphotypes and/or features are taxonomically diagnostic below 'dicotyledon' level. The findings constitute a foundation upon which future research can build, refining and expanding our knowledge of the North-western European region.

Background and aims: Tropical forests exchange more carbon dioxide (CO2) with the atmosphere than any other terrestrial biome. Yet, uncertainty in the projected carbon balance over the next century is roughly three-times greater for the tropics than other ecosystems. Our limited knowledge of tropical plant physiological responses, including photosynthetic, to climate change is a substantial source of uncertainty in our ability to forecast the global terrestrial carbon sink.

Methods: We used a meta-analytic approach, focusing on tropical photosynthetic temperature responses, to address this knowledge gap. Our dataset, gleaned from 18 independent studies, included leaf-level light saturated photosynthetic (Asat) temperature responses from 108 woody species, with additional temperature parameters (35 species) and rates (250 species) of both maximum rates of electron transport (Jmax) and Rubisco carboxylation (Vcmax). We investigated how these parameters responded to mean annual temperature (MAT), temperature variability, aridity, and elevation, as well as also how responses differed among successional strategy, leaf habit, and light environment.

Key results: Optimum temperatures for Asat (ToptA) and Jmax (ToptJ) increased with MAT but not for Vcmax (ToptV). Although photosynthetic rates were higher for "light" than "shaded" leaves, light conditions did not generate differences in temperature response parameters. ToptA did not differ with successional strategy, but early successional species had ~4 °C wider thermal niches than mid/late species. Semi-deciduous species had ~1 °C higher ToptA than broadleaf evergreen. Most global modeling efforts consider all tropical forests as a single "broadleaf evergreen" functional type, but our data show that tropical species with different leaf habits display distinct temperature responses that should be included in modeling efforts.

Conclusions: This novel research will inform modeling efforts to quantify tropical ecosystem carbon cycling and provide more accurate representations of how these key ecosystems will respond to altered temperature patterns in the face of climate warming.

Background and aims: Flower colour is a key feature in plant-pollinator interactions that make the flowers visible amid the surrounding green vegetation. Green flowers are expected to be scarcely conspicuous to pollinators; however, many of them are visited by pollinators even in the absence of other traits that might attract pollinators (e.g., floral scents). In this study, we investigate how entomophilous species with green flowers are perceived by pollinators.

Methods: We obtained reflectance spectra data of 30 European species that display green or green-yellow flowers to the human eye. These data were used to perform spectral analyses, calculate both chromatic (colour contrast against the background) and achromatic (colour contrast that relies on the signals from the green-sensitive photoreceptors) cues, and model colour perception by hymenopterans (bees) and dipterans (flies).

Key results: The visibility of green flowers to bees and flies (i.e., their chromatic contrast values) was lower compared to other floral colours commonly pollinated by these insects, whereas green-yellow flowers were as conspicuous as the other flower colours. Green flowers with low chromatic contrast values exhibited higher achromatic contrasts, which is used to detect distant flowers at narrow visual angles, than green-yellow flowers. Additionally, the marker points (i.e., sharp transition in floral reflectance that aid pollinators in locating them) of green and green-yellow flowers aligned to some degree with the colour discrimination abilities of bees and flies.

Conclusions: We found that many entomophilous green and green-yellow flowers are conspicuous to bees and flies through their chromatic or achromatic contrasts. While acquiring pigments like carotenoids, which impart a yellowish hue to flowers and enhances their visibility to pollinators, could increase their conspicuousness, the metabolic costs of pigment production, along with the use of alternative strategies to attract pollinators, may have constrained carotenoid emergence in certain lineages of green-flowered species.

Background and aims: The whole-plant economics spectrum (PES) describes coordination between organ-level traits that together determine resource use strategies and is relevant for understanding plant responses to environmental change. Whereas coordination between organs has previously been explored across species, it remains unclear whether patterns observed across species hold within species. In addition, the key driving forces underlying this coordination warrant clarification.

Methods: In this study we used univariate (regression analysis) and multivariate (principal components analysis, network analysis) analyses to investigate the environmental drivers of intraspecific trait variation (ITV) and consequently, trait covariation, focusing on leaf and fine root traits. We sampled 60 individuals of Schima superba, a widespread evergreen tree, across five elevations in a subtropical forest in China, measuring traits associated with resource use and capture, including photosynthesis, specific root length and root diameter.

Key results: Leaf and root traits were significantly correlated within species, forming a PES. We found that plants at low and high elevation had more resource acquisitive traits than at intermediate elevation. Notably, leaf and root traits, as well as a composite variable that contained both, varied nonlinearly with elevation. Leaf trait variation was driven primarily by temperature, whereas root trait variation and a composite variable containing leaf and root traits, was most strongly influenced by temperature and plant-available soil phosphorus.

Conclusions: Our findings show that the coordinated responses of individual traits to climate and soil properties underlie intraspecific variation in whole-plant resource use strategies across environmental gradients. These findings are contrary to recent studies that have found evidence of decoupling between above- and below-ground traits, which suggests that there is selection for coordination among traits in S. superba. Thus, our study enhances our understanding of the key drivers, as well as the ecological significance of environmentally-driven ITV.

Background: Floral adaptations supposedly favour pollen grains to cross the numerous barriers faced during their journey to stigmas. Stamen dimorphism and specialized petals, like the cucculus in the Cassieae tribe (Fabaceae), are commonly observed in flowers that offer only pollen as a resource for bee pollinators. Here, we experimentally investigated whether the stamen dimorphism and cucculus enhance pollen placement on the bee's body.

Methods: We used 3D-printed bee models to apply artificial vibrations on the flowers of Chamaechrista latistipula with their cucculus deflected or maintained in its original position and their anther pores manipulated. After each simulated flower visit, we captured photographs of the artificial bee from four distinct angles. Employing digital imaging techniques, we documented the presence and location of pollen and stigma on the bee's body.

Key results: Our findings reveal that the cucculus redistributes pollen grains on the bee's body. There is a remarkable increase in pollen density (approximately tenfold) on the lateral side adjacent to the cucculus, precisely where the stigma contacts the bee when the cucculus is unmanipulated. Furthermore, the cucculus also enhances pollen placement on the ventral region of the bee, indicating its additional function. The cucculus also increases the accuracy of pollen grains on the adjacent lateral region of the bee's body, irrespective of the pollen grains released by small or large anthers.

Conclusions: Floral specialized traits, such as modified petals and stamen dimorphism, can modify the fate of pollen grains and ultimately contribute to the male reproductive performance in pollen flowers with poricidal anthers. The cucculus exhibits a dual role by promoting pollen placement in optimal regions for pollination and probably supporting pollen grains for bee feeding. These findings provide valuable insights into the adaptive significance of floral traits and their impact on the reproductive success of pollen flowers.