Annals of botany最新文献

Background and aims: Worldwide, climate change and human activities are accelerating the decline and mortality of adult trees, largely driven by hydraulic dysfunction. While the hydraulic limitation hypothesis (HLH) is well-documented in tall trees, its relevance to the decline of tall shrubs remains poorly understood. Although widely distributed across China, the dioecious shrub Hippophae rhamnoides is experiencing widespread decline. However, the role of height-related hydraulic constraints in shrub decline, especially among dioecious species, is still unclear.

Methods: To evaluate potential hydraulic constraints, we investigated natural H. rhamnoides on the Qinghai-Tibetan Plateau (QTP), measuring stem hydraulic conductivity, leaf gas exchange parameters, and xylem anatomy across individuals of different heights using standard hydraulic and microscopy techniques. This approach enabled assessment of height-related variation in hydraulic efficiency and carbon fixation.

Key results: We found: (i) sapwood-specific hydraulic conductivity (Kₛ) and net photosynthetic rate (Pₙ) decreased with increasing height, which supports the HLH in shrubs, however, stomatal conductance (gₛ) remained stable with increasing height, a pattern inconsistent with the stomatal regulation predicted by the HLH. Moreover, the reduction in hydraulic conductivity correlates with increased water potential (Ψ), lower vessel density (VD), and larger hydraulically weighted mean vessel diameter (Dₕ); (ii) the structural equation model (SEM) revealed a height-driven compensatory mechanism: reduced sapwood density (WD) resulting from height growth increased Kₛ and Pn, enabling H. rhamnoides to survive for decades after decay; (iii)during the decline stage, taller males exhibited lower Kₛ, leaf-specific hydraulic conductivity (Kₗ), and WD, yet higher Ψ, than females, indicating sexually dimorphic hydraulic traits associated with height differences.

Conclusions: Despite compensatory adjustments, height-related hydraulic constraints and reduced photosynthesis drive the H. rhamnoides decline, with hydraulic sexual dimorphism linked to height divergence. Our results provide a theoretical basis for tall-shrubs decline and hydraulic sexual dimorphism, supporting vegetation restoration and conservation strategies.

Background and aims: Distinctive bicarpellate, elongate, capsular fruits from the early to middle Eocene Green River flora of Colorado, Utah and Wyoming, USA, previously named Danaea coloradensis Knowlton 1923, match those of Carpolithus scalariformis Reid and Chandler 1933 from the early Eocene London Clay flora of southern England. We call attention to this biogeographical disjunction, revise the taxonomic nomenclature, and investigate the morphology and potential affinities of the newly recognized genus, Scalarifructus.

Methods: Fossils were investigated by reflected light and X-ray micro-computed tomography scanning, with external morphology provided by the impression fossils and internal anatomy by the permineralized fruits.

Key results: Although specimens from the Green River Formation are preserved as impressions in shale, they match well with the morphology preserved in the pyrite-permineralized specimens from the London Clay Formation, and are considered to be conspecific. Anatomically preserved fruits from the London Clay provide details of internal tissues of the pericarp and seeds, while impression specimens from the Green River give additional features of the exocarp. Scalarifructus coloradensis (Knowlton) gen. et sp. comb. nov. fruits are septicidal capsules bearing two rows of seeds per carpel in parietal placentation, separated longitudinally by a false septum.

Conclusions: Although these fruits from floras ca. 47-53 Ma do not match any extant genus, and even the familial assignment remains elusive, their morphology is consistent with features found today in the order Brassicales. The occurrence of this taxon in North America and Europe parallels previously recognized disjunctions between the Palaeogene floras of Europe and Cordilleran North America.

Background and aims: Acrocomia is a Neotropical palm genus that recently gained attention for its potential as a multipurpose crop. Among its species, A. aculeata and A. totai stand out for their potential in sustainable biofuel production and ecosystem restoration. Despite their relevance, the genomic structure and domestication history of these species remain poorly understood. This study aims to characterize the genetic structure and diversity of A. aculeata and A. totai across their natural distribution, to understand the biogeographic processes behind their differentiation, and to investigate the domestication history of A. aculeata through a genetic, ecological, archaeobotanical, and ethnographic lens.

Methods: We used double-digest genotyping-by-sequencing (ddGBS) to analyze 85 individuals of A. aculeata and 11 of A. totai from nine countries. Genomic structure was assessed using sNMF, DAPC, and NJ methods. For A. aculeata, we performed ecological niche modeling during the Pliocene and genome scans to identify outlier SNPs within the major genetic groups. These results were integrated with archaeobotanical and ethnographic data to contextualize domestication patterns.

Key results: We identified nine highly structured genetic clusters with low gene flow, confirming two major gene pools: Central and South America, shaped by Pleistocene-Holocene biogeographic dynamics. Using SNPs under selection, we found three regional clusters in A. aculeata: Central America, Amazonia, and southeastern Brazil. Functional annotation revealed lineage-specific genes linked to agronomic traits: disease resistance, dwarfism, and fruit development in Central America, and lipid metabolism and transcriptional regulation in South America, which may be related to independent domestication pathways over the past 13,000 years.

Conclusions: Our findings offer new insights into the evolutionary and biocultural history of Acrocomia, supporting the existence of distinct evolutionary trajectories. These results highlight the species' potential for sustainable development and emphasize the need for just strategies that include traditional communities in contemporary production systems.

Background and aims: Trade-offs between current reproduction and future performance are fundamental constraints on evolution. In dioecious plants, females and males may differ in how much of a limiting resource they allocate to reproduction, creating trade-offs that could be sex-specific and environmentally dependent. If so, physiological differences in resource use are expected to coincide with differential costs of reproduction for females versus males, but how these costs are expressed across environmental contexts remains poorly understood.

Methods: We tested the hypothesis that the expression of sex-specific reproductive trade-offs is environmentally dependent in dioecious broadleaf arrowhead (Sagittaria latifolia). We conducted a two-year common garden experiment manipulating nutrient availability and reproductive investment to quantify sex-specific physiological costs using photosynthetic measurements and indices of nitrogen content.

Key results: As expected, the expression of reproductive trade-offs depended on both sex and resource availability. At the lowest nutrient level, males experienced reproductive costs as reduced leaf nitrogen content and photosynthesis following flowering in year 1, and as reduced leaf leaf nitrogen content and size in year 2. Across all nutrient conditions, females showed fewer detectable physiological costs.

Conclusions: Together with results from previous studies of S. latifolia, our study shows that males and females incur reproductive costs in different physiological currencies, with males allocating more nitrogen than females. These costs become evident only under nitrogen limitation, highlighting how environmental context governs the expression of sex-specific life-history trade-offs.

Background and aims: Plant elicitor peptides (Peps), which originate from their precursor proteins known as PROPEPs, play essential roles as signaling molecules that modulate both plant defense responses and developmental processes.

Methods: In this study, we investigated the role of PROPEP2 and its derived peptide Pep2, in regulating root hair development in Arabidopsis thaliana. Root hairs at different growth stages along the primary root and in distinct zones of the root tip were analyzed. We further examined the relationship between Pep2 and auxin signaling in regulating root hair growth.

Key results: Our findings indicate that loss of PROPEP2 function results in markedly decreased root hair number and elongation during the primary root development phase, whereas root hair formation during the embryonic root stage remains unaffected. Notably, exogenous Pep2 application rescued these defects and even induced root hair formation in non-hair-forming regions. We further demonstrated that Pep2 enhances root hair growth by stimulating localized auxin production in the root tip region. The mutants defective in auxin production (yuc1 yuc4 and wei8 tar1 tar2) failed to respond to Pep2. Furthermore, we identified the receptor-like kinases FERONIA (FER) and [Ca2+]cyt-associated protein kinase 1 (CAP1) as critical components of the Pep2 signaling pathway, with mutations in these genes impairing root hair growth and rendering plants unresponsive to Pep2.

Conclusions: These results uncover a previously uncharacterized interaction between Pep2 and auxin signaling components in the regulation of root hair development, offering additional insights into the molecular control of root morphology.

Background and aims: Climate change is resulting in increasingly variable weather patterns with spikes of high temperatures adversely affecting crop production. Here the effect of elevated temperature just before harvest was investigated in wild rocket (Diplotaxis tenuifolia (L.) DC.), a popular brassicaceous salad. The key aim was to investigate how pre-harvest stress affects postharvest responses.

Methods: Mature rocket plants were subjected to 3 days of elevated day time temperature (35 °C) before harvest. Leaves were then stored at 6 °C to mimic postharvest supply chain conditions. Physiological data were collected at harvest and after 7, 14 and 21 days of storage. Volatile organic compounds (VOCs) were analysed by gas chromatography mass spectrometry, changes in metabolite profiles were analysed through flow injection electrospray high-resolution mass spectroscopy, gene expression was assessed by RNAseq and real time PCR.

Key results: Transcriptomic analysis showed a mild heat stress signature affecting both metabolic and regulatory genes, including those related to hormone signalling. Models for effects on circadian clock genes and regulation of cold/dark stress responses are derived based on Arabidopsis thaliana pathways. After 7 days of storage, there were also significant effects of the pre-harvest heat stress on leaf VOC profiles, with distinct patterns compared to those at harvest. The metabolome was also affected after 7 days of storage, with specific effects on several lipid classes, amino acids and sugars. However, the direction of gene expression changes did not always match effects on VOCs. After 21 days of storage, pre-harvest heat stress adversely affected chlorophyll content and photosynthetic capacity, promoted ion leakage, and resulted in increased stomatal closure.

Conclusions: Cold storage affects the physiology, gene expression and metabolome of rocket leaves and these effects are perturbed by exposure to heat stress before harvest.

Background and aims: Cycads are the most threatened group of seed plants, with isolation and habitat fragmentation among the primary drivers of species decline. Understanding how genetic diversity is distributed across populations is crucial for informing conservation management and identifying genetically vulnerable populations that require conservation attention.

Methods: Here, we investigated the genetic diversity and structure of two endemic Australian species of significant conservation concern, Cycas armstrongii and C. maconochiei subsp. maconochiei. 236 individuals were sampled from 26 populations across their native ranges, including a presumed putative hybrid population (C. armstrongii × maconochiei), utilising next-generation sequencing in the form of restriction site-associated DNA sequencing (RADseq).

Key results: Our results suggested low levels of genetic diversity in both taxa (C. armstrongii (He ≤ 0.038); C. maconochiei subsp. maconochiei (He ≤ 0.061)) and no evidence for inbreeding (mean GIS = -0.143 and -0.153, respectively). Analysis of molecular variance (AMOVA) indicated minimal genetic differentiation between populations (2.41%) and between taxa (1.81%). However, pairwise FST values and Mantel test revealed significant isolation by distance (r = 0.606, P < 0.0001). Discriminant analysis of principal components (DAPC), STRUCTURE analysis indicated admixture. Morphological traits, principal component and environmental analysis based on seven traits, found significant differentiation in five characters, four of which were environmentally linked. The results showed no clear signal of interspecific hybridisation for either taxon.

Conclusions: These findings indicate C. armstrongii and C. maconochiei subsp. maconochiei likely represents a morphologically variable species. In addition to updating the threat assessment, we recommend: (1) formally recognising genetically depauperate or geographically isolated populations (e.g. Tiwi Islands) as Conservation Management Units (CMUs); (2) establishing new ex-situ assurance collections for at-risk CMUs; and (3) implementing assisted gene flow among genetically compatible populations to enhance adaptive potential. These actions will ensure conservation strategies are tailored to evolutionary and ecological units.

Background and aims: A low ratio of red to far-red radiation (R:FR ratio) is a signal of competition for light in plant canopies. Plants exposed to low R:FR ratios typically display reduced accumulation of chemical defenses against herbivorous insects. In Arabidopsis and other model plants, this effect of low R:FR ratios has been explained on the basis of changes in jasmonate metabolism and signaling. In the genus Solanum, volatile organic compounds (VOCs), mainly terpenoids produced in trichome glands and released to the environment, are very important signaling molecules involved in plant interactions with insect herbivores. Our aim was to investigate the effect of low R:FR ratios on the terpenes produced and released by plants of the wild tomato species Solanum habrochaites and its consequences on the behavior of the specialist herbivore Tuta absoluta.

Methods: Plants of S. habrochaites (ac LA2167) were exposed to white light (WL) or WL supplemented with FR and used to evaluate morphological responses, VOC production and emissions, and herbivore attractiveness.

Key results: S. habrochaites plants responded to low R:FR ratios with the typical shade avoidance syndrome, characterized by elongated shoots and hyponastic leaves. This morphological response to low R:FR ratios was accompanied by a reduction in the content and emission of 7-epizingiberene, which correlated with reduced expression of two biosynthetic genes (zFPS and ShZIS) in type-VI trichome glands. Finally, choice bioassays demonstrated that T. absoluta moths preferred plants from the FR treatment over control (WL) plants, a result consistent with the reduced production of 7-epizingiberene, which is known for its insect repellent properties.

Conclusions: Collectively, our results suggest that terpene accumulation in glandular trichomes in S. habrochaites is regulated by light at the transcriptional level, and that this regulation could have important consequences for plant resistance to herbivory in plant stands.

Background and aims: Many carnivorous plants rely on open fluid pools or droplets to trap and digest arthropod prey. Here we investigate for Nepenthes rafflesiana pitcher plants how they maintain functional fluid pools inside their traps while growing in open sites exposed to changing weather conditions. We hypothesised that very low or high fluid levels reduce the pitcher's trapping success and that pitchers possess mechanisms to minimise fluctuations of the fluid level.

Methodology: Natural fluid levels of N. rafflesiana pitchers were monitored in the field. Fluid level effects on prey capture rate and efficiency were quantified with field and laboratory experiments. To test the capacity of plants to respond to changes in fluid level, we experimentally simulated flooding by adding water to pitchers, and evaporation by replacing the contents with a smaller volume of concentrated pitcher fluid.

Key results: Freshly opened N. rafflesiana pitchers were approximately halfway filled with fluid. Over a five-week observation period, daily fluctuations of pitcher fluid levels were significantly lower than those of water-filled control vials. Pitchers possess canopy-like lids, but this did not eliminate rainwater influx into pitchers. Both low and very high fluid levels were detrimental to prey capture, with intermediate fluid levels yielding the highest trapping rate. Experimentally flooded pitchers returned to intermediate fluid levels within 2-3 days. Pitchers responded to simulated evaporation by secreting fluid, restoring intermediate fluid levels within 2 days. These homeostatic responses may be triggered by fluid volume, or water potential gradients resulting from concentration changes.

Conclusions: N. rafflesiana pitchers regulate their fluid level and remain efficient insect traps under fluctuating weather conditions. This active control is a previously unrecognised pitcher plant adaptation to their exposed habitats; understanding it is important for predicting ability of these plants to withstand extreme weather conditions enhanced by climate change.