Summary
In seasonally cold climates, many woody plants tolerate chilling and freezing temperatures by ceasing growth, shedding leaves and entering dormancy. At the same time, transport within these ...plants often decreases as the vascular system exhibits reduced functionality. As spring growth requires water and nutrients, we ask the question: how much does bud, leaf and flower development depend on the vasculature in spring? In this review, we present what is known about leaf, flower and vascular phenology to sort out this question. In early stages of bud development, buds rely on internal resources and do not appear to require vascular support. The situation changes during organ expansion, after leaves and flowers reconnect to the stem vascular system. However, there are major gaps in our understanding of the timing of vascular development, especially regarding the phloem, as well as the synchronization among leaves, flowers, stem and root vasculature. We believe these gaps are mainly the outcome of research completed in silo and urge future work to take a more integrative approach. We highlight current challenges and propose future directions to make rapid progress on this important topic in upcoming years.
Premise of the Study
New growth in the spring requires resource mobilization in the vascular system at a time when xylem and phloem function are often reduced in seasonally cold climates. As a ...result, the timing of leaf out and/or flowering could depend on when the vascular system resumes normal function in the spring. This study investigated whether flowering time is influenced by vascular phenology in plants that flower precociously before they have leaves.
Methods
Flower, leaf, and vascular phenology were monitored in pairs of precocious and non‐precocious congeners. Differences in resource allocation were quantified by measuring bud dry mass and water content throughout the year, floral hydration was modelled, and a girdling treatment completed on branches in the field.
Key Results
Precocious flowering species invested more in floral buds the year before flowering than did their non‐precocious congeners, thus mobilizing less water in the spring, which allowed flowering before new vessel maturation.
Conclusions
A shift in the timing of resource allocation in precocious flowering plants allowed them to flower before the production of mature vessels and minimized the significance of seasonal changes in vascular function to their flowering phenology. The low investment required to complete floral development in the spring when the plant vascular system is often compromised could explain why flowers can emerge before leaf out.
Summary
Many woody plants produce large floral displays early in the spring when xylem transport can be variable and often reduced. To determine whether stem hydraulics impact floral water use, we ...quantified floral transpiration and tested whether it was correlated with stem xylem conductivity in five temperate woody species that flower before producing leaves.
We measured inflorescence gas exchange, examined the relationship between diffusive conductance and inflorescence morphology, and estimated the amount of water supplied to an inflorescence by the phloem. We also tested for correlation between transpiration and native stem xylem conductivity for branches with leaves and branches with flowers.
The flowers of our study species obtain most of their water from the xylem. Diffusive conductance was higher in small inflorescences, but water content and daily transpiration rates were greater for larger inflorescences. We found no correlation between floral transpiration per branch and stem xylem conductivity within species.
The data suggest that inflorescence water loss during anthesis is not limited by the xylem in our study species. We highlight the impact of floral morphology on hydraulic traits and encourage exploration into temporal shifts in floral hydration.
Despite the crucial role of carbon transport in whole plant physiology and its impact on plant–environment interactions and ecosystem function, relatively little research has tried to examine how ...phloem physiology impacts plant ecology. In this review, we highlight several areas of active research where inquiry into phloem physiology has increased our understanding of whole plant function and ecological processes. We consider how xylem–phloem interactions impact plant drought tolerance and reproduction, how phloem transport influences carbon allocation in trees and carbon cycling in ecosystems and how phloem function mediates plant relations with insects, pests, microbes and symbiotes. We argue that in spite of challenges that exist in studying phloem physiology, it is critical that we consider the role of this dynamic vascular system when examining the relationship between plants and their biotic and abiotic environment.
This review highlights the important but understudied role of phloem physiology in mediating how plants interact with their biotic and abiotic environment and shaping larger ecological patterns. We focus on three critical areas of current research: interactions between the xylem and phloem, carbon fluxes both in plants and at the ecosystem scale and interactions between plants and their biotic environment. The goal of this review is to draw attention to the critical role of carbon transport in plant physiological ecology and outline many of the questions that remain to be answered about this critical part of the plant vascular system.
Background The gut microbiome in infancy influences immune system maturation, and may have an important impact on allergic disease risk. Objective We sought to determine how prenatal and early life ...factors impact the gut microbiome in a relatively large, ethnically diverse study population of infants at age 3 to 6 months, who were enrolled in Vitamin D Antenatal Asthma Reduction Trial, a clinical trial of vitamin D supplementation in pregnancy to prevent asthma and allergies in offspring. Methods We performed 16S rRNA gene sequencing on 333 infants' stool samples. Microbial diversity was computed using the Shannon index. Factor analysis applied to the top 25 most abundant taxa revealed 4 underlying bacterial coabundance groups; the first dominated by Firmicutes ( Lachnospiraceae / Clostridiales ), the second by Proteobacteria ( Klebsiella / Enterobacter ), the third by Bacteriodetes , and the fourth by Veillonella . Scores for coabundance groups were used as outcomes in regression models, with prenatal/birth and demographic characteristics as independent predictors. Multivariate analysis, using all microbial community members, was also conducted. Results White race/ethnicity was associated with lower diversity but higher Bacteroidetes coabundance scores. C-section birth was associated with higher diversity, but decreased Bacteroidetes coabundance scores. Firmicutes scores were higher for infants born by C-section. Breast-fed infants had lower proportions of Clostridiales . Cord blood vitamin D was linked to increased Lachnobacterium , but decreased Lactococcus. Conclusions The findings presented here suggest that race, mode of delivery, breast-feeding, and cord blood vitamin D levels are associated with infant gut microbiome composition, with possible long-term implications for immune system modulation and asthma/allergic disease incidence.
Background
Alterations in the intestinal microbiome are prospectively associated with the development of asthma; less is known regarding the role of microbiome alterations in food allergy ...development.
Methods
Intestinal microbiome samples were collected at age 3‐6 months in children participating in the follow‐up phase of an interventional trial of high‐dose vitamin D given during pregnancy. At age 3, sensitization to foods (milk, egg, peanut, soy, wheat, walnut) was assessed. Food allergy was defined as caretaker report of healthcare provider‐diagnosed allergy to the above foods prior to age 3 with evidence of IgE sensitization. Analysis was performed using Phyloseq and DESeq2; P‐values were adjusted for multiple comparisons.
Results
Complete data were available for 225 children; there were 87 cases of food sensitization and 14 cases of food allergy. Microbial diversity measures did not differ between food sensitization and food allergy cases and controls. The genera Haemophilus (log2 fold change −2.15, P=.003), Dialister (log2 fold change −2.22, P=.009), Dorea (log2 fold change −1.65, P=.02), and Clostridium (log2 fold change −1.47, P=.002) were underrepresented among subjects with food sensitization. The genera Citrobacter (log2 fold change −3.41, P=.03), Oscillospira (log2 fold change −2.80, P=.03), Lactococcus (log2 fold change −3.19, P=.05), and Dorea (log2 fold change −3.00, P=.05) were underrepresented among subjects with food allergy.
Conclusions
The temporal association between bacterial colonization and food sensitization and allergy suggests that the microbiome may have a causal role in the development of food allergy. Our findings have therapeutic implications for the prevention and treatment of food allergy.
Summary
There is a long‐standing idea that the timing of leaf production in seasonally cold climates is linked to xylem anatomy, specifically vessel diameter because of the hydraulic requirements of ...expanding leaves.
We tested for a relationship between the timing of leaf out and vessel diameter in 220 plants in three common gardens accounting for species’ phylogenetic relationships. We investigated how vessel diameter related to wood porosity, plant height and leaf length. We also used dye perfusion tests to determine whether plants relied on xylem produced during the previous growing season at the time of leaf out.
In all three gardens, there was later leaf out in species with wider vessels. Ring‐porous species had the widest vessels, exhibited latest leaf out and relied less on xylem made during the previous growing season than diffuse‐porous species. Wood anatomy and leaf phenology did not exhibit a phylogenetic signal.
The timing of leaf out is correlated with wood anatomy across species regardless of species’ geographic origin and phylogenetic relationships. This correlation could be a result of developmental and physiological links between leaves and wood or tied to a larger safety efficiency trade‐off.
See also the Commentary on this article by Olson, 235: 815–820.
With increasing concern about the ecological consequences of global climate change, there has been renewed interest in understanding the processes that determine species range limits. We tested a ...long-hypothesized trade-off between freezing tolerance and growth rate that is often used to explain species range limits. We grew 24 willow and poplar species (family Salicaceae) collected from across North America in a greenhouse common garden under two climate treatments. Maximum entropy models were used to describe species distributions and to estimate species-specific climate parameters. A range of traits related to freezing tolerance, including senescence, budburst, and susceptibility to different temperature minima during and after acclimation were measured. As predicted, species from colder climates exhibited higher freezing tolerance and slower growth rates than species from warmer climates under certain environmental conditions. However, the average relative growth rate (millimeters per meter per day) of northern species markedly increased when a subset of species was grown under a long summer day length (20.5 h), indicating that genetically based day-length cues are required for growth regulation in these species. We conclude that the observed relationship between freezing tolerance and growth rate is not driven by differences in species' intrinsic growth capacity but by differences in the environmental cues that trigger growth. We propose that the coordinated evolution of freezing tolerance and growth phenology could be important in circumscribing willow and poplar range limits and may have important implications for species' current and future distributions.
Background Endocrine-disrupting compounds (EDCs) have immune-modulating effects. We were interested in determining their association with allergic sensitization. Objective We sought to determine the ...association between EDCs and allergic sensitization and whether this relationship depends on the antimicrobial properties of the EDCs, sex, or both. Methods Data were obtained from the 2005-2006 National Health and Nutrition Examination Survey in which urinary bisphenol A; triclosan; benzophenone-3; propyl, methyl, butyl, and ethyl parabens; and specific IgE levels were available for 860 children. Aeroallergen and food sensitizations were defined as having at least 1 positive (≥0.35 kU/L) specific IgE level to an aeroallergen or a food. Logistic regression was used to determine the association of EDCs and sensitization. Analyses were adjusted for urinary creatinine level, age, sex, ethnicity, and poverty index ratio. Results The odds of aeroallergen sensitization significantly increased with the level of the antimicrobial EDCs triclosan and propyl and butyl parabens ( P ≤ .04). The odds of food sensitization significantly increased with the level of urinary triclosan among male subjects (odds ratio for third vs first tertiles, 3.9; P = .02 for trend). There was a significant interaction between sex and triclosan level, with male subjects being more likely to be food sensitized with exposure ( P = .03). Similar associations were not identified for the nonantimicrobial EDCs bisphenol A and benzophenone-3 ( P > .2). Conclusions As a group, EDCs are not associated with allergen sensitization. However, levels of the antimicrobial EDCs triclosan and parabens were significantly associated with allergic sensitization. The potential role of antimicrobial EDCs in allergic disease warrants further study because they are commonly used in Western society.
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