Annals of botany最新文献

Background and aims: The circadian clock is a time-keeping mechanism that detects of and responds to temporal environmental changes. Despite functional hypotheses of circadian resonance, in which the match between endogeneous circadian rhythms and exogenous environmental cycles is presumed to be adaptive, considerable genetic variation is observed in clock parameters. The circadian parameter of period length, for instance, exhibits significant segregating genetic variation within and among populations along an elevational cline in Boechera stricta. This variation may reflect variable selection on circadian timing of biological functions and clock outputs across environmental microsites. Reproductive timing is an important clock output and selection may favor accelerated or delayed phenology.

Methods: We performed a three-year common garden field study with the short-lived perennial Boechera stricta (Brassicaceae) to quantify life history differences. We studied individuals from 20 populations along an elevational gradient and from 20 maternal families derived from a single population. We measured days to bolting and later life-history transitions such as days to flowering; in the same genotypes, we measured circadian period and assessed correlations between phenology and clock traits.

Key results: The timing of all life-history transitions varied among growing seasons, suggesting adaptive life-history evolution to local climate conditions. Life-history transitions after bolting were associated with circadian period, such that lengthened period correlated with delayed life-history transitions. Structural equation modeling indicated that indirect selection via days to flowering and fruit production favored lengthened clock period in the low elevation common garden site.

Conclusions: We found a direct, directional effect of the environment on phenology, and indirect selection on the circadian clock through phenology. Our results suggest that selection on phenology could explain the evolution of variable circadian periods observed among populations from differing environments.

Background and aims: Adansonia suarezensis, one of Madagascar's six endemic baobab species, is currently classified as Endangered by the IUCN Red List and faces severe risks from habitat loss and climate change, being predicted to become extinct by 2080 if no conservation actions are taken. We combined population genomics with ecological surveys to assess the genetic diversity, population structure, and regeneration dynamics of this species across representative sites.

Methods: We generated SNP data from 118 mature individuals sampled across four sites using a target capture approach and evaluated genetic diversity, inbreeding, and population structure. Ecological surveys were conducted at Mahory and Beantely, representing the two genetic clusters, to compare forest structure, floristic composition, and regeneration dynamics. Vertebrate diversity was also recorded to assess its potential influence on regeneration.

Key results: Population genomic analyses identified two moderately differentiated genetic groups, with Mahory clearly distinct from the northern localities. Pairwise FST values ranged from 0.054 to 0.133, all statistically significant (p = 0.001). Despite low overall genetic diversity, no evidence of inbreeding was detected, consistent with bat-mediated cross-pollination. Ecological surveys revealed higher species richness, greater structural diversity, and stronger regeneration signals in Mahory, especially in core zones, compared with Beantely. By contrast, regeneration in Beantely was weak, with few saplings and juveniles despite relatively high adult densities. These differences likely reflect stronger edge effects, greater disturbance, and lower animal diversity at Beantely, which may limit pollination and seed dispersal.

Conclusions: Our results demonstrate that A. suarezensis is structured into two genetic groups with low but significant differentiation and that regeneration failure is widespread, but most pronounced in degraded edge habitats. Conservation strategies should therefore prioritize the protection of core forest zones, safeguard pollinator and disperser communities, and reinforce natural regeneration through targeted restoration. By integrating genomic and ecological perspectives, this study provides essential guidance for the long-term conservation of A. suarezensis.

Background and aims: Fire acts as a primary ecological filter, influencing the structure, composition, and evolutionary pathways of savanna ecosystems globally. While numerous savanna tree species exhibit resprouting, the impact of fire on seed quality remains poorly understood. Using Caryocar brasiliense, a keystone tree species in the Cerrado, as a model, this study examines whether post-fire trees prioritize vegetative recovery to restore canopy function, potentially limiting resources allocated to reproduction and, consequently, reducing both reproductive output and seed reserve concentrations.

Methods: Structural responses, reproductive phenology, and seed traits were assessed in two 3-ha Cerrado sensu stricto areas: one burned and one unburned. Forty adult trees were monitored for structural responses, and 20 individuals for phenological over a 30-month period. Seeds from the first post-fire reproductive cycle were collected; 120 were analyzed for mass, viability, and germination, and 50 were used for biochemical-reserve quantification. We applied GLM/GLMM models and complementary tests.

Key results: Although the survival rate was 95%, the fire caused significant structural damage. Fifty-two percent of individuals experienced topkill. Branch number and crown area decreased by 28% and 56%, respectively, with minimal recovery observed over 30 months. Reproductive activity was suppressed for two cycles and resumed only after 25 to 27 months at a reduced level. Seeds from burned trees exhibited lower mass, approximately 20% lower viability, and diminished lipid and carbon reserves. However, germination rates remained similar between treatments.

Conclusions: Fire-induced structural damage and diminished seed quality demonstrate that a single burn event can restrict the short-term reproductive capacity of Cerrado trees. Such limitations may impede population recovery, highlighting the importance of extended fire-free intervals to facilitate canopy restoration and high-quality seeds. The findings indicate that the structural and physiological impacts of a single fire may endure for considerable periods before the ecosystem restores its pre-fire ecological functions.

Background and aims: Sphenophytes, now restricted to Equisetum, were more diverse during the Paleozoic, particularly within Carboniferous coal swamp ecosystems. Despite their significance, the origins and phylogenetic relationships of sphenophytes with stem-group monilophytes remain poorly understood. In this context, the extinct order Pseudoborniales, typified by Pseudobornia ursina (Nathorst, 1894) from the Late Devonian of Bjørnøya (Norway), plays a key role in understanding the group's origin. However, conflicting interpretations of its reproductive structures have hindered its phylogenetic placement. Here, we provide a new description and reconstruction of the reproductive structures of P. ursina to evaluate its phylogenetic relationships with other sphenophytes and closely-allied groups, as well as to provide an updated perspective on the evolution of key traits among sphenopsids.

Methods: Fossils from the type locality were re-examined to clarify the morphology of the strobilus and fertile appendages. Comparative analyses were conducted with members of Sphenophyllales, Equisetales, and stem-group monilophytes. Phylogenetic relationships were assessed using parsimony and Bayesian methods.

Key results: The strobilus of P. ursina displays distinctive features: (1) stalked, sporangia-bearing appendage, (2) oblique insertion of these structures in the bract axil, (3) ∼30 erect sporangia arranged on a wide-obconical receptacle, and (4) deeply bisected bracts with entire margins and parallel venation. Vegetative characters suggest equisetalean affinities, while reproductive traits more closely resemble stem sphenopsids. This mosaic points to a unique combination of ancestral traits within Sphenopsida, and phylogenetic analyses place P. ursina within Equisetales.

Conclusions: Our reappraisal of the strobilus of Pseudobornia ursina clarifies both its morphology and its phylogenetic placement, being recovered as part of stem Equisetales, sister to Archaeocalamitaceae. This suggests an evolutionary scenario where fertile appendages of stem sphenophytes became more compact over time, with either a fusion to a bract or the development of fertile internodes, combined to the loss of the bract, leading to the two main clades of Sphenophytes (Sphenophyllales and Equisetales).

Background and aims: Species with small geographic ranges provide insights into adaptation, speciation, and genetic drift, while also presenting clear conservation challenges. Homoranthus A.Cunn. ex Schauer (Myrtaceae), an Australian genus with many narrow endemics, offers a model for understanding how ecological and spatial factors drive diversification. We examined a regional hotspot with a high number of Homoranthus narrow endemics to assess patterns of genetic diversity and inform both evolutionary understanding and conservation planning.

Methods: We generated genome-wide SNP data using DArTseq for 282 individuals across 13 Homoranthus species (40% of the genus), including ten narrow endemics, to assess population genetic structure and diversity.

Key results: All species showed strong genetic isolation, even over a few kilometres, with populations diverging within hundreds of meters. Homoranthus lunatus includes two highly divergent, non-sister lineages, suggesting taxonomic revision. Inbreeding was common but unrelated to range size, and heterozygosity remained moderate, indicating intrinsic buffering of genetic diversity. Genome sizes were notably small relative to other angiosperms.

Conclusions: Ecological isolation, life-history traits, and limited dispersal drive both speciation and extinction risk in Homoranthus. Diversification and endemism are linked to habitat fragmentation, highlighting the need for conservation strategies that address ecological connectivity as well as species protection.

Background and aims: Island-endemic plants with narrow geographic ranges are highly vulnerable to invasive herbivores and climate change, which can reduce reproductive success and shift their distributions. To understand how these pressures shape population connectivity, we studied two endemic violets (Viola cheiranthifolia and V. guaxarensis) from El Teide, Canary Islands.

Methods: We examined genetic diversity and related it to climatic and topographic variables using linear models. To assess how landscape features affect gene flow, we applied gravity models at the population level in V. cheiranthifolia (163 individuals) and in 48 V. guaxarensis individuals (one population).

Key results: We found no significant correlation between genetic diversity and environmental variables in V. cheiranthifolia. While greater herbivore densities did not appear to decrease connectivity, larger violet populations, including those protected from herbivory, showed greater connectivity. Geographic distance limited genetic exchange in V. cheiranthifolia, whereas diurnal temperature changes, precipitation, and slope were key factors explaining connectivity in V. guaxarensis. Future projections indicated minimal changes in gene flow patterns for both species.

Conclusions: Conservation measures that increase population density enhance genetic connectivity in these endangered endemic violets. Furthermore, understanding how specific landscape variables shape connectivity can directly inform restoration efforts in targeted areas. By identifying key connectivity hubs and zones most in need of intervention, our research offers practical strategies for enhancing the resilience of this unique island flora.

Background and aims: Diverging secondary sex ratios in dioecious plant species often deviate from the expected 1:1 primary male-to-female ratio due to differential survival rates. Such deviations in life-history strategies, along with diverging reproductive trade-offs, have been used for assessing reproductive costs in plants. In the fire-prone Fynbos biome, previous studies on sex ratios and reproductive costs in dioecious Proteaceae have produced conflicting results, warranting further investigation. We examined whether obligate reseeding serotinous Leucadendron and Aulax species (Proteaceae) experience higher reproductive cost in males, females, or both equally.

Methods: We analysed sex ratios across populations of varying ages and assessed individual health through canopy cover scores. In addition, we conducted nutrient analysis to quantify allocation to vegetative versus reproductive structures.

Key results: We found no evidence that primary sex ratios differ from 1:1, but clear evidence of secondary sex ratios becoming increasingly male biased with age. Predictions indicated that a typical 30-year-old population would have a sex ratio of 0.67 (95% CI, [0.52, 0.81]), corresponding to a twice as many males than females. In older, more male-biased populations, females exhibited lower health scores. While total nutrient content did not differ between the sexes, females allocated a greater proportion of total nutrients to their reproductive cone structures.

Conclusions: Our results suggest that females experience higher reproductive costs which contribute to increased female mortality over time, resulting in male-biased sex ratios in older populations. Anthropogenic fire suppression likely contributes to this trend by allowing populations to survive beyond the natural fire-return interval for fynbos vegetation. These altered population dynamics could undermine long-term population viability and ecosystem stability in fire-adapted dioecious Proteaceae of the fynbos.

Background and aims: It is assumed that trees should adapt their above- and below-ground organs as they age. However, most studies to date have quantified these trait adjustments in homogeneous forest stands, confounding the effect of stand ageing on soil properties and the intrinsic response of trees to ageing.

Methods: Here, we examined 11 morphological, architectural, anatomical and mycorrhizal fine root traits of each of the first five orders for 66 Pinus koraiensis individuals aged 16-285 years old in northeast China, while accounting for soil characteristics (pH and total C, N and P concentrations).

Key results: Across all absorptive root orders, Hartig net area and mantle thickness, representative of P. koraiensis reliance on ectomycorrhizal association, displayed an orthogonal pattern to traits describing root economics strategy, specific root length and root tissue density. Hartig net area and mantle thickness were not significantly related to root mycorrhizal colonization intensity and root branching intensity. As trees aged, there was a trade-off between increasing specific root length and decreasing root tissue density in all root orders we measured. Trees facing soil conditions with lower N or P concentrations showed higher dependence on ectomycorrhizal fungi.

Conclusions: This work provides evidence that tree below-ground economics strategy can change significantly throughout their lifetime. In the ectomycorrhizal tree species studied, morphological adjustments are most pronounced, whereas mycorrhizal strategy remains largely consistent. The more conservative root strategy of younger trees than older ones contradicts previous results on the ageing of homogeneous tree stands, suggesting that individual tree responses to ageing in mixed-aged forests might differ strongly from those in homogeneous forest stands experiencing multiple confounding environmental influences.

Background and aims: Root water uptake (RWU) is influenced by rhizosphere conductance and soil-root contact, which vary with soil texture and root structure, including root hairs. Current simplified models often fail to capture the spatial complexity of these interactions in drying soils. The aim of this study was to examine how rhizosphere conductance, soil-root contact and root hairs affect RWU.

Methods: We used an explicit three-dimensional functional-structural model to investigate how root and rhizosphere hydraulics influence the transpiration rate-leaf water potential relationship of two maize (Zea mays) genotypes (with and without root hairs) grown in two contrasting soil textures (loam and sand) during soil drying. The model incorporated rhizosphere resistance in series with radial root resistance, with the latter being influenced by maturation (development of apoplastic barriers with age). It considered two critical processes: (1) the decrease in soil water potential between bulk soil and the soil-root interface; and (2) the extent of soil-root contact.

Key results: The simulations revealed that RWU was highly soil texture specific. In loam, the non-linearity in the transpiration rate-leaf water potential relationship was attributable primarily to localized uptake fluxes and high rhizosphere resistance as soil dried. In sand, however, where soil-root contact was less effective, rhizosphere conductance became a significant limiting factor for RWU, even at relatively higher soil water potential in comparison to loam. Root hairs did not make a significant contribution to rhizosphere conductance, probably owing to the dominant effect of soil-root interaction. Additionally, variations in root hydraulic conductance and its change with root tissue age impacted the accuracy of the model.

Conclusions: The explicit three-dimensional model provides a more precise representation of RWU dynamics by pinpointing exact uptake locations and primary limiting factors and by quantifying the proportion of root surface actively engaged in RWU. This approach offers notable improvements over conventional models for understanding the spatial dynamics of water uptake in different soil environments.

Background and aims: Root axes with greater penetration ability are often considered to be beneficial in hard soils. We hypothesized that maize root phenotypes with greater plasticity (meaning reduced elongation in response to mechanical impedance, i.e. a 'stop signal') have fitness advantages over phenotypes with reduced plasticity (i.e. unimpeded root elongation) in native (virgin, uncultivated) soils, by reallocating root foraging to softer, presumably wetter, soil domains, and that the value of the stop signal reduced with soil cultivation and crop domestication.

Methods: We used OpenSimRoot to simulate native and cultivated soils and evaluated maize root phenotypes with varying axial and lateral root penetration ability in water, nitrogen (N) and impedance regimes associated with Neolithic agriculture.

Key results: The stop signal was advantageous in native soils but was less beneficial in cultivated, irrigated soils. Reduced root foraging in hard, dry topsoil enabled root growth in deeper domains where water is available, resulting in an improved balance of resource expenditure and acquisition. The value of the stop signal declined during crop domestication with the advent of irrigation, which increased water availability in the topsoil. Soil cultivation reduced N availability, while irrigation increased N leaching, resulting in a shift in the fitness landscape, with greater lateral root length (i.e. reduced plasticity) being advantageous by colocalizing root foraging with N availability. The importance of the stop signal is evident in modern high-input systems in which drought is a limiting factor.

Conclusions: Our results support the hypotheses that the reduction of lateral root growth by mechanical impedance is adaptive in native soil, but became less adaptive with soil cultivation and irrigation associated with Neolithic agriculture.