A diverse and distinct microbiome inside living trees.

Despite significant advances in microbiome research across various environments, the microbiome of Earth's largest biomass reservoir-the wood of living trees-remains largely unexplored. Here, we illuminate the microbiome inhabiting and adapted to wood and further specialized to individual host tree species, revealing that wood is a harbour of biodiversity and potential key players in tree health and forest ecosystem functions. We demonstrate that a single tree hosts approximately one trillion bacteria in its woody tissues, with microbial communities distinctly partitioned between heartwood and sapwood, each maintaining unique microbiomes with minimal similarity to other plant tissues or ecosystem components.

Ice and air: Visualisation of freeze-thaw embolism and freezing spread in young L. tulipifera leaves.

Spring freezing is an unforgiving stress for young leaves, often leading to death, with consequences for tree productivity and survival. While both the plant water transport system and living tissues are vulnerable to freezing, we do not know whether damage to one or both of these systems causes death in leaves exposed to freezing. Whole saplings of Liriodendron tulipifera were exposed to freezing and thawing trajectories designed to mimic natural spring freezes.

In situ cavitation bubble manometry reveals a lack of light-activated guard cell turgor modulation in bryophytes.

Diversification of plant hydraulic architecture and stomatal function coincides with radical changes in the Earth's atmosphere over the past 400 my. Due to shared stomatal anatomy with the earliest land plants, bryophyte stomatal behavior may provide insights into the evolution of stomatal function, but significant uncertainty remains due to technical limitations of measuring guard cell turgor pressure in situ. Here, we introduce a method for monitoring cell turgor pressure by nucleating microbubbles within the guard cells of intact plant tissue and then examining microbubble growth and dissolution dynamics.

Palisade cell geometry in relation to leaf optical and photosynthetic properties in Viburnum.

The optical properties of lobed palisade mesophyll cells remain poorly understood despite their presence in diverse taxa and the critical role of the palisade layer in leaf-light interactions and carbon assimilation. Using microcomputed tomography, 3D ray tracing simulations, and physiological experiments, we tested the interactions among palisade cell geometry, chloroplast localization, light directional quality, and leaf optical and photosynthetic performance in the model taxon Viburnum. Simulations showed that lobed cells shifted between absorptance- and transmittance-dominated states depending on chloroplast localization, irrespective of light directional quality.

Sensitive Hydraulic and Stomatal Decline in Extreme Drought Tolerant Species of California Ceanothus.

Identifying the physiological mechanisms by which plants are adapted to drought is critical to predict species responses to climate change. We measured the responses of leaf hydraulic and stomatal conductances (K and g, respectively) to dehydration, and their association with anatomy, in seven species of California Ceanothus grown in a common garden, including some of the most drought-tolerant species in the semi-arid flora. We tested for matching of maximum hydraulic supply and demand and quantified the role of decline of K in driving stomatal closure.

Stomatal closure as a driver of minimum leaf conductance declines at high temperature and vapor pressure deficit in Quercus.

Rising global temperatures and vapor pressure deficits (VPDs) are increasing plant water demand and becoming major drivers of large-scale plant mortality. Controlling transient leaf water loss after stomatal closure (minimum stomatal conductance [gmin]) is recognized as a key trait determining how long plants survive during soil drought. Yet, substantial uncertainty remains regarding how gmin responds to elevated temperatures and VPD and the underlying mechanisms.

Wind speed affects the rate and kinetics of stomatal conductance.

Understanding the relationship between wind speed and gas exchange in plants is a longstanding challenge. Our aim was to investigate the impact of wind speed on maximum rates of gas exchange and the kinetics of stomatal responses. We conducted experiments in different angiosperm and fern species using an infrared gas analyzer equipped with a controlled leaf fan, enabling precise control of the boundary layer conductance.

Weak link or strong foundation? Vulnerability of fine root networks and stems to xylem embolism.

Resolving the position of roots in the whole-plant hierarchy of drought-induced xylem embolism resistance is fundamental for predicting when species become isolated from soil water resources. Published research generally suggests that roots are the most vulnerable organ of the plant vascular system, although estimates vary significantly. However, our knowledge of root embolism excludes the fine roots (< 2 mm diameter) that form the bulk of total absorptive surface area of the root network for water and nutrient uptake.

Stomatal behaviour and water relations in ferns and lycophytes across habits and habitats.

Stomatal anatomy and behaviour are key to managing gas exchange fluxes, which require coordination with the plant vascular system to adequately supply leaves with water. Stomatal response times and regulation of water loss are generally understudied in ferns, especially across habits (i.e.

Starch depletion in the xylem and phloem ray parenchyma of grapevine stems under drought.

While nonstructural carbohydrate (NSC) storage can support long-lived woody plants during abiotic stress, the timing and extent of their use are less understood, as are the thresholds for cell mortality as NSCs and water supplies are consumed. Here, we combine physiological and imaging tools to study the response of to a 6-week experimental drought. We focused on the spatial and temporal dynamics of starch consumption and cell viability in the xylem and phloem of the stem.

Anatomy of an agricultural antagonist: Feeding complex structure and function of three xylem sap-feeding insects illuminated with synchrotron-based 3D imaging.

Many insects feed on xylem or phloem sap of vascular plants. Although physical damage to the plant is minimal, the process of insect feeding can transmit lethal viruses and bacterial pathogens. Disparities between insect-mediated pathogen transmission efficiency have been identified among xylem sap-feeding insects; however, the mechanistic drivers of these trends are unclear.

Back to life: Techniques for developing high-quality 3D reconstructions of plants and animals from digitized specimens.

Expanded use of 3D imaging in organismal biology and paleontology has substantially enhanced the ability to visualize and analyze specimens. These techniques have improved our understanding of the anatomy of many taxa, and the integration of downstream computational tools applied to 3D datasets have broadened the range of analyses that can be performed (e.g.

Localized growth and remodelling drives spongy mesophyll morphogenesis.

The spongy mesophyll is a complex, porous tissue found in plant leaves that enables carbon capture and provides mechanical stability. Unlike many other biological tissues, which remain confluent throughout development, the spongy mesophyll must develop from an initially confluent tissue into a tortuous network of cells with a large proportion of intercellular airspace. How the airspace in the spongy mesophyll develops while the tissue remains mechanically stable is unknown.

Hydraulic failure as a primary driver of xylem network evolution in early vascular plants.

The earliest vascular plants had stems with a central cylindrical strand of water-conducting xylem, which rapidly diversified into more complex shapes. This diversification is understood to coincide with increases in plant body size and branching; however, no selection pressure favoring xylem strand-shape complexity is known. We show that incremental changes in xylem network organization that diverge from the cylindrical ancestral form lead to progressively greater drought resistance by reducing the risk of hydraulic failure.

Pathogen-induced hydraulic decline limits photosynthesis and starch storage in grapevines (Vitis sp.).

Xylella fastidiosa (Xf) is the bacterial pathogen responsible for Pierce's Disease (PD) in grapevine (Vitis vinifera L.) and numerous diseases in agriculturally and ecologically important species. Current theory suggests that localized inoculations via insect feeding lead to bacterial spread through the xylem, reducing water transport capacity, leading to declines in productivity, and ultimately death.

Desiccation of the leaf mesophyll and its implications for CO diffusion and light processing.

Leaves balance CO and radiative absorption while maintaining water transport to maximise photosynthesis. Related species with contrasting leaf anatomy can provide insights into inherent and stress-induced links between structure and function for commonly measured leaf traits for important crops. We used two walnut species with contrasting mesophyll anatomy to evaluate these integrated exchange processes under non-stressed and drought conditions using a combination of light microscopy, X-ray microCT, gas exchange, hydraulic conductance, and chlorophyll distribution profiles through leaves.

Desiccation and rehydration dynamics in the epiphytic resurrection fern Pleopeltis polypodioides.

The epiphytic resurrection-or desiccation-tolerant (DT)-fern Pleopeltis polypodioides can survive extreme desiccation and recover physiological activity within hours of rehydration. Yet, how epiphytic DT ferns coordinate between deterioration and recovery of their hydraulic and photosynthetic systems remains poorly understood. We examined the functional status of the leaf vascular system, chlorophyll fluorescence, and photosynthetic rate during desiccation and rehydration of P.

Ecologically driven selection of nonstructural carbohydrate storage in oak trees.

Leaf habit is a major axis of plant diversity that has consequences for carbon balance since the leaf is the primary site of photosynthesis. Nonstructural carbohydrates (NSCs) produced by photosynthesis can be allocated to storage and serve as a resiliency mechanism to future abiotic and biotic stress. However, how leaf habit affects NSC storage in an evolutionary context has not been shown.

By the narrowest of margins: nano-scale modification of pit membranes and the fate of plants during drought. A commentary on: 'Intervessel pit membrane thickness best explains variation in embolism resistance amongst stems of Arabidopsis thaliana accessions'.

This article comments on: Ajaree Thonglim, Sylvain Delzon, Maximilian Larter, Omid Karami, Arezoo Rahimi, Remko Offringa, Joost J. B. Keurentjes, Salma Balazadeh, Erik Smets and Frederic Lens, Intervessel pit membrane thickness best explains variation in embolism resistance amongst stems of accessions, , Volume 128, Issue 2, 23 July 2021, Pages 171–182, 10.

Linking xylem network failure with leaf tissue death.

Global warming is expected to dramatically accelerate forest mortality as temperature and drought intensity increase. Predicting the magnitude of this impact urgently requires an understanding of the process connecting atmospheric drying to plant tissue damage. Recent episodes of forest mortality worldwide have been widely attributed to dry conditions causing acute damage to plant vascular systems.

Maximum CO diffusion inside leaves is limited by the scaling of cell size and genome size.

Maintaining high rates of photosynthesis in leaves requires efficient movement of CO from the atmosphere to the mesophyll cells inside the leaf where CO is converted into sugar. CO diffusion inside the leaf depends directly on the structure of the mesophyll cells and their surrounding airspace, which have been difficult to characterize because of their inherently three-dimensional organization. Yet faster CO diffusion inside the leaf was probably critical in elevating rates of photosynthesis that occurred among angiosperm lineages.

Diversification, disparification and hybridization in the desert shrubs Encelia.

There are multiple hypotheses for the spectacular plant diversity found in deserts. We explore how different factors, including the roles of ecological opportunity and selection, promote diversification and disparification in Encelia, a lineage of woody plants in the deserts of the Americas. Using a nearly complete species-level phylogeny based on double-digest restriction-aided sequencing along with a broad set of phenotypic traits, we estimate divergence times and diversification rates, identify instances of hybridization, quantify trait disparity and assess phenotypic divergence across environmental gradients.

Seasonal coordination of leaf hydraulics and gas exchange in a wintergreen fern.

Wintergreen fern has fronds that are photosynthetically active year-round, despite diurnal and seasonal changes in soil moisture, air temperature and light availability. This species can fix much of its annual carbon during periods when the deciduous canopy is open. Yet, remaining photosynthetically active year-round requires the maintenance of photosynthetic and hydraulic systems that are vulnerable to freeze-thaw cycles.