Elevated nutrient supply can exert worse effects on Norway spruce than drought, viewed through chemical defence against needle rust.

Abiotic factors such as water and nutrient availability can exert a dominant influence on the susceptibility of plants to various pathogens. Effects of abiotic environmental factors on phenolic compound concentrations in the plant tissue may represent one of the major underlying mechanisms, as these compounds are known to play a substantial role in plant resistance to pests. In particular, this applies to conifer trees, in which a large range of phenolic compounds are produced constitutively and/or induced by pathogen attack.

Advances in understanding Norway spruce natural resistance to needle bladder rust infection: transcriptional and secondary metabolites profiling.

Background: Needle rust caused by the fungus Chrysomyxa rhododendri causes significant growth decline and increased mortality of young Norway spruce trees in subalpine forests. Extremely rare trees with enhanced resistance represent promising candidates for practice-oriented reproduction approaches. They also enable the investigation of tree molecular defence and resistance mechanisms against this fungal disease.

The 2018 European heatwave led to stem dehydration but not to consistent growth reductions in forests.

Heatwaves exert disproportionately strong and sometimes irreversible impacts on forest ecosystems. These impacts remain poorly understood at the tree and species level and across large spatial scales. Here, we investigate the effects of the record-breaking 2018 European heatwave on tree growth and tree water status using a collection of high-temporal resolution dendrometer data from 21 species across 53 sites.

Tracheid and Pit Dimensions Hardly Vary in the Xylem of Under Contrasting Growing Conditions.

Maintaining sufficient water transport the xylem is crucial for tree survival under variable environmental conditions. Both efficiency and safety of the water transport are based on the anatomical structure of conduits and their connections, the pits. Yet, the plasticity of the xylem anatomy, particularly that of the pit structures, remains unclear.

Alpine dwarf shrubs show high proportions of nonfunctional xylem: Visualization and quantification of species-specific patterns.

Xylem conductive capacity is a key determinant of plant hydraulic function and intimately linked to photosynthesis and productivity, but can be impeded by temporary or permanent conduit dysfunctions. Here we show that persistent xylem dysfunctions in unstressed plants are frequent in Alpine dwarf shrubs and occur in various but species-specific cross-sectional patterns. Combined synchrotron micro-computed tomography (micro-CT) imaging, xylem staining, and flow measurements in saturated samples of six widespread Ericaceae species evidence a high proportion (19%-50%) of hydraulically nonfunctional xylem areas in the absence of drought stress, with regular distribution of dysfunctions between or within growth rings.

Hydraulic-stomatal coordination in tree seedlings: tight correlation across environments and ontogeny in Acer pseudoplatanus.

Hydraulic conductance is recognized as a major determinant of gas exchange and productivity. However, whether this also applies to seedlings, a critically important stage for vegetation regeneration, has been largely unknown. We analyzed the hydraulic and stomatal conductance of leaves and shoots for 6-wk-old Acer pseudoplatanus seedlings emerging in different lowland and treeline habitats and under glasshouse conditions, respectively, as well as on 9-, 15- and 18-wk-old plants, and related findings to leaf and xylem anatomical traits.

Subalpine dwarf shrubs differ in vulnerability to xylem cavitation: An innovative staining approach enables new insights.

Dwarf shrubs are a key functional group of the high-elevation vegetation belt. Despite their ecological relevance and high sensitivity to environmental changes, the hydraulic adaptations and species-specific variations in drought tolerance within this growth form are mostly unknown. Here, we assess the xylem vulnerability to cavitation of important character species of the Alpine dwarf shrub heaths in Central Europe.

From the comfort zone to crown dieback: Sequence of physiological stress thresholds in mature European beech trees across progressive drought.

Drought responses of mature trees are still poorly understood making it difficult to predict species distributions under a warmer climate. Using mature European beech (Fagus sylvatica L.), a widespread and economically important tree species in Europe, we aimed at developing an empirical stress-level scheme to describe its physiological response to drought.

Insights into trunks of L.: analyses of hydraulics via electrical resistivity tomography.

Key Message: The lack of elevational changes in electrical resistivity in trunks indicated consistent growth and hydraulics across elevations. Though, electrical resistivity tomograms exhibited pronounced temperature-driven seasonal changes.

Abstract: Alpine conifers growing at high elevation are exposed to low temperatures, which may limit xylogenesis and cause pronounced seasonal changes in tree hydraulics.

RNA-Seq and secondary metabolite analyses reveal a putative defence-transcriptome in Norway spruce (Picea abies) against needle bladder rust (Chrysomyxa rhododendri) infection.

Background: Norway spruce trees in subalpine forests frequently face infections by the needle rust fungus Chrysomyxa rhododendri, which causes significant growth decline and increased mortality of young trees. Yet, it is unknown whether trees actively respond to fungal attack by activating molecular defence responses and/or respective gene expression.

Results: Here, we report results from an infection experiment, in which the transcriptomes (via RNA-Seq analysis) and phenolic profiles (via UHPLC-MS) of control and infected trees were compared over a period of 39 days.

Noninvasive Analysis of Tree Stems by Electrical Resistivity Tomography: Unraveling the Effects of Temperature, Water Status, and Electrode Installation.

The increasing demand for tree and forest health monitoring due to ongoing climate change requires new future-oriented and nondestructive measurement techniques. Electrical resistivity (ER) tomography represents a promising and innovative approach, as it allows insights into living trees based on ER levels and ER cross-sectional distribution patterns of stems. However, it is poorly understood how external factors, such as temperature, tree water status, and electrode installation affect ER tomograms.

Electrical resistivity tomography: patterns in Betula pendula, Fagus sylvatica, Picea abies and Pinus sylvestris.

Electrical resistivity (ER) tomography is a promising technique to minimally invasively study stems of living trees. It allows insights into xylem properties based on the cross-sectional distribution of ER that is governed by the wood's electrical conductance. In this study, ER measurements were carried out on four forest tree species, Betula pendula, Fagus sylvatica, Picea abies and Pinus sylvestris, to demonstrate interspecific, intraspecific and within-tree variation of ER tomograms.

Are hydraulic patterns of lianas different from trees? New insights from Hedera helix.

Lianas form long and flexible but disproportionately narrow stems, and thus require particular strategies to maintain the integrity of xylem water transport and ensure supply to large crown areas. The hydraulic architecture of lianas and the respective within-plant coordination of transport efficiency and safety, and the underlying anatomical variations in xylem, are largely unexplored. We analysed Hedera helix, a liana widespread in European temperate forests, with respect to hydraulic and xylem anatomical variations between the main stem and branches, between juvenile and adult life phases, and along the vertical axis.

Insights from in vivo micro-CT analysis: testing the hydraulic vulnerability segmentation in Acer pseudoplatanus and Fagus sylvatica seedlings.

The seedling stage is the most susceptible one during a tree's life. Water relations may be crucial for seedlings due to their small roots, limited water buffers and the effects of drought on water transport. Despite obvious relevance, studies on seedling xylem hydraulics are scarce as respective methodical approaches are limited.

The pitfalls of in vivo imaging techniques: evidence for cellular damage caused by synchrotron X-ray computed micro-tomography.

Synchrotron X-ray computed micro-tomography (microCT) has emerged as a promising noninvasive technique for in vivo monitoring of xylem function, including embolism build-up under drought and hydraulic recovery following re-irrigation. Yet, the possible harmful effects of ionizing radiation on plant tissues have never been quantified. We specifically investigated the eventual damage suffered by stem living cells of three different species exposed to repeated microCT scans.

Robustness of xylem properties in conifers: analyses of tracheid and pit dimensions along elevational transects.

In alpine regions, tree hydraulics are limited by low temperatures that restrict xylem growth and induce winter frost drought and freezing stress. While several studies have dealt with functional limitations, data on elevational changes in functionally relevant xylem anatomical parameters are still scarce. In wood cores of Pinus cembra L.

Foliar Phenolic Compounds in Norway Spruce with Varying Susceptibility to : Analyses of Seasonal and Infection-Induced Accumulation Patterns.

Secondary phenolic metabolites are involved in plant responses to various biotic stress factors, and are apparently important for the defense against fungal pathogens. In this study, we investigated their role in defense against the rust in Norway spruce. The fungal pathogen undergoes a seasonal lifecycle with host shift; after overwintering in rhododendron shrubs, it attacks the sprouting current-year spruce needles and causes needle fall in autumn.

Association genetics of phenolic needle compounds in Norway spruce with variable susceptibility to needle bladder rust.

Accumulation of phenolic needle metabolites in Norway spruce is regulated by many genes with small and additive effects and is correlated with the susceptibility against fungal attack. Norway spruce accumulates high foliar concentrations of secondary phenolic metabolites, with important functions for pathogen defence responses. However, the molecular genetic basis underlying the quantitative variation of phenolic compounds and their role in enhanced resistance of spruce to infection by needle bladder rust are unknown.

Herb Hydraulics: Inter- and Intraspecific Variation in Three Ranunculus Species.

The requirements of the water transport system of small herbaceous species differ considerably from those of woody species. Despite their ecological importance for many biomes, knowledge regarding herb hydraulics remains very limited. We compared key hydraulic features (vulnerability to drought-induced hydraulic decline, pressure-volume relations, onset of cellular damage, in situ variation of water potential, and stomatal conductance) of three Ranunculus species differing in their soil humidity preferences and ecological amplitude.

Dwarf shrub hydraulics: two Vaccinium species (Vaccinium myrtillus, Vaccinium vitis-idaea) of the European Alps compared.

Vaccinium myrtillus and Vaccinium vitis-idaea are two dwarf shrubs widespread in the European Alps. We studied the hydraulics of these species hypothesizing that (1) the hydraulic architecture of dwarf shrubs differs from trees, (2) hydraulic properties reflect the species' ecological amplitude and (3) hydraulic properties vary spatially and seasonally. Key hydraulic parameters (osmotic potential, turgor loss point, xylem hydraulic conductivity, vulnerability to drought-induced embolism, stomata closure, drought-induced cell damage and embolism repair) and related wood anatomical traits (conduit diameter and conduit wall reinforcement) were analyzed at four sites in Tyrol, Austria.