Structural deviations in secondary phloem of young shoots of Spiraea beauverdiana near magma volcanoes

We performed a comparative analysis of the internal structure of the secondary phloem of one, two and three-year-old stems of Spiraea beauverdiana growing in extreme conditions of solfataric fields of Golovnin Volcano caldera and Mendeleyev Volcano and in normal conditions. The combination of environmental factors in conditions of solfataric activity, such as high temperatures in the soil and in the near-surface air, as well as saturation with gases toxic to plants, rare elements accumulating in the nearby substrate, and lack of soil moisture, interfere with normal phellogen and cambium activity. Deviations from the normal structure involve changes in the following parameters of the internal structure of a year-old stem of S. beauverdiana. Secondary phloem parameters in the studied habitats are normal, except for the length of the segments of sieve tubes, the height of single-row rays, the length of parenchymal girder; these are shorter in S. beauverdiana stems from volcanos. At two and three years of age in volcanic conditions we see reduction in the width of the secondary phloem (both conductive and non-conductive) and the diameter of the segments of sieve tubes. In samples from Golovnin Volcano we see reduction in tangential diameter, while in the samples from Mendeleyev Volcano it’s the radial diameter. We also see reduction in the height of multiple-row rays. At that age we see changes in the structure of the radial parenchyma; namely, we find no double-row rays in samples from Golovnin Volcano caldera. One of the signs of impact of volcanic activity on the bark structure is development of non-specific anomalies in the internal structure of the S. beauverdiana bark, namely, in the outer bark, or in deeper levels, such as the secondary phloem. That causes sclerification and dilatation of parenchyma, and multiple layers in some tissues.

Bark Effects on Stemflow Chemistry in a Japanese Temperate Forest I. The Role of Bark Surface Morphology

Stemflow can be an important pathway for the drainage of precipitation and related solutes through tree canopies to forest soils. As stemflow must drain along bark surfaces, the effects of bark structure on stemflow chemical composition is merited. This study examines the relationship between stemflow chemistry and bark surface structure for six species of varying bark morphology (four deciduous broadleaf trees and two evergreen coniferous trees) at a montane and an urban site in Japan. Stemflow from smooth-barked species contained greater concentrations of solutes that appear to be rinsed from the stem surface (i.e., sea salt aerosols); while, rougher-barked tree species contained greater or less concentrations of solutes that appear to be leached (e.g., Ca2+) or taken-up (e.g., inorganic N) by the bark, respectively. Site-specific atmospheric environments also influenced thee bark-stemflow chemistry relationships—where the greater elemental deposition in the urban plot generally resulted in greater stemflow chemistry than observed in the lower-deposition montane plot. Our results therefore suggest that the dynamics of dry deposition wash-off by stemflow, and the exchange of dissolved solutes between stemflow and the bark surface, are influenced by the surface structure of the bark and the site’s atmospheric environment. Therefore, the interactions between bark surface structure and its surrounding atmospheric environment are important factors in the stemflow-related elemental cycling between the tree and precipitation.

Hypothesis and Theory: Fungal Spores in Stemflow and Potential Bark Sources

The study of stemflow fungi began over 50 years ago. Past work has been performed in different climatic regions of the world, with different sampling methods, by mycologists focusing on different taxonomical groups. Therefore, we aim to synthesize this work to delineate major conclusions and emerging hypothesis. Here, we present: (1) a systematic compilation of observations on stemflow conidial concentration, flux, and species composition; (2) an evaluation of the methods underlying these observations; (3) a testable theory to understand spatiotemporal dynamics in stemflow (including honeydews) conidial assemblages, with a focus on their relationship to bark structure and microhabitats; and (4) a discussion of major hypotheses based on past observations and new data. This represents a knowledge gap in our understanding of fungal dispersal mechanisms in forests, in a spatially-concentrated hydrologic flux that interacts with habitats throughout the forest microbiome. The literature synthesis and new data represent observations for 228 fungal species’ conidia in stemflow collected from 58 tree species, 6 palm species, and 1 bamboo species. Hypothetical relationships were identified regarding stemflow production and conidial concentration, flux, and species composition. These relationships appear to be driven by bark physico-chemical properties, tree canopy setting, the diversity of in-canopy microenvironments (e.g., tree holes, bark fissures, and epiphytes), and several possible conidia exchange processes (teleomorph aerosols, epi-faunal exchanges, fungal colonization of canopy microhabitats, and droplet impacts, etc.). The review reveals a more complex function of stemflow fungi, having a role in self-cleaning tree surfaces (which play air quality-related ecoservices themselves), and, on the other hand, these fungi may have a role in the protection of the host plant.

Hygroscopic contributions to bark water storage and controls exerted by internal bark structure over water vapor absorption

Key message Hygroscopicity is a crucial element of bark water storage and can reach >60% of water holding capacity of bark depending on tree species Abstract Bark forms the outer layer of woody plants, and it is directly exposed to wetting during rainfall and reacts to changes in relative humidity, i.e., it may exchange water with the atmosphere through absorption and desorption of water vapor. A current paradigm of bark hydrology suggests that the maximum water storage of bark empties between precipitation events and is principally controlled by bark thickness and roughness. We hypothesize that (1) the ability of bark to absorb water vapor during non-rainfall periods (i.e., hygroscopicity) leads to partial saturation of bark tissues during dry periods that may alter the rate of bark saturation during rainfall, and (2) the degree of bark saturation through hygroscopic water is a function of internal bark structure, including porosity and density, that varies among species. To address these questions, we conducted laboratory experiments to measure interspecific differences in bark physical structure as it relates to water storage mechanisms among common tree species (hickory (Carya spp.), oak (Quercus spp.), sweetgum (Liquidambar styraciflua), and loblolly pine (Pinus taeda)) in the southeastern United States. Furthermore, we considered how these properties changed across total bark, outer bark, and inner bark. We found a distinct difference between hickory and oak, whereby hickory had 5.6% lower specific density, 31.1% higher bulk density, and 22.4% lower total porosity of outer bark resulting in higher hygroscopicity compared to oaks. For all species, hygroscopicity increased linearly with bulk density (R2 = 0.65–0.81) and decreased linearly with total porosity (R2 = 0.64–0.88). Overall, bark hygroscopicity may constitute an average of 30% of total bark water storage capacity. Therefore, in humid climates like those of the southeastern USA, the proportion of bark that remains saturated during non-storm conditions should not be considered negligible.

Wood and bark anatomy of South African Picrodendraceae with systematic and ecological implications

Wood and bark structure of Androstachys johnsonii and Hyaenanche globosa (Picrodendraceae) is described. Two species share simple perforation plates, minute to small intervessel pits, and nonseptate fibres; these traits also reported in other Picrodendraceae. Androstachys is distinctive in having scanty paratracheal axial parenchyma and uniseriate rays with vessel-ray pits restricted to marginal cells. Bordered pits on fibre walls is an ancestral condition for the African Picrodendraceae. High vessel frequency and vessel grouping in Androstachys can be adaptive for semi-arid climate with wet summer. Both genera share the subepidermal phellogen initiation and the presence of thick-walled fibers and sclereids in secondary phloem. In Hyaenanche, the bark is dilated by stretching and divisions of parenchyma cells with formation of pseudocortex. Androstachys shows no ray dilatation, but sclerification of its parenchyma can make substantial contribution in bark expansion. Abundant trichomes on epidermis of young shoots of Androstachys are presumably involved in the water uptake from mists.

Vitality versus cambium, xylem, and phloem characteristics in Cedrus libani

In many regions, such as the Mediterranean, anticipated climate change is seen as a serious threat to tree vitality and forest productivity. Recent studies show that wood and bark structure as well as the number of dormant cambial cells bear valuable information about the growth condition and vitality of trees and thus could function as indicators to help manage forests in the future. Microcores and tree cores were sampled from stems of adult Cedrus libani trees growing at different altitudes in SW-Turkey. Trees were divided into two groups based on basal area increments: vital trees (positive growth trend), and trees of diminishing vitality (negative growth trend). Histological cross-sections were investigated for their number of dormant cambial cells as well as their xylem and phloem characteristics. We measured the widths of the conducting phloem, most recent xylem ring, earlywood, and latewood. We further calculated the ratio between the width of xylem ring and conducting phloem (XR:CPH ratio), and earlywood to latewood ratio. Vital trees had a significantly higher number of dormant cambial cells (on average 32%), higher xylem (67%), and conducting phloem (36%) widths, and a higher XR:CPH ratio (47%). The XR:CPH ratio ranged between 1.8:1 and 21.4:1. The number of dormant cambial cells was closely related to xylem and conducting phloem widths and showed a significant decrease with tree age. Altitude showed no direct effect on the measured and calculated parameters. Our results indicate the potential of dormant cambium, xylem, and phloem characteristics to assess the vitality and growth conditions of C. libani trees.

Diurnal Pine Bark Structure Dynamics Affect Properties Relevant to Firebrand Generation

Firebrands are an important agent of wildfire spread and structure fire ignitions at the wildland urban interface. Bark flake morphology has been highlighted as an important yet poorly characterized factor in firebrand generation, transport, deposition, and ignition of unburned material. Using pine species where bark flakes are the documented source of embers, we conducted experiments to investigate how bark structure changes in response to diurnal drying. Over a three-day period in a longleaf pine (Pinus palustris Mill.) stand in Florida, we recorded changes in temperature, moisture content, and structure of bark across different facing aspects of mature pine trees to examine the effects of varying solar exposure on bark moisture. We further compared results to bark drying in a pitch pine (Pinus rigida Mill.) plantation in New Jersey. Under all conditions, bark peeled and lifted away from the tree trunk over the study periods. Tree bole aspect and the time of day interacted to significantly affect bark peeling. General temperature increases and moisture content decreases were significantly different between east and west aspects in pitch pine, and with time of day and aspect in longleaf pine. These results illustrate that bark moisture and flakiness is highly dynamic on short time scales, driven largely by solar exposure. These diurnal changes likely influence the probability of firebrand production during fire events via controls on moisture (ignition) and peeling (lofting).

Diurnal Pine Bark Structure Dynamics Affect Properties Relevant to Firebrand Generation

Firebrands are an important agent of wildfire spread and structure fire ignitions at the wildland urban interface. Bark flake morphology has been highlighted as an important, yet poorly characterized factor in firebrand generation, transport, deposition, and ignition of unburned material. Using pine species where bark flakes are the documented source of embers, we conducted experiments to investigate how bark structure changes in response to diurnal drying. Over a 3-day period in a longleaf pine (Pinus palustris Mill.) stand in Florida, we recorded changes in temperature, moisture content and structure of bark across different facing aspects of mature pine trees to examine the effects of varying solar exposure on bark moisture. We further compared results to bark drying in a pitch pine (Pinus rigida Mill.) plantation in New Jersey. Under all conditions, bark peeled and lifted away from the tree trunk over the study periods. Tree bole aspect and the time of day interacted to significantly affect bark peeling. General temperature increases and moisture content decreases were significantly different between east and west aspects in pitch pine, and with time of day and aspect in longleaf pine. These results illustrate that bark moisture and flakiness is highly dynamic on short time scales, driven largely by solar exposure. These diurnal changes likely influence the probability of firebrand production during fire events via controls on moisture (ignition) and peeling (lofting).

Wood and bark of Buddleja: uniseriate phellem, and systematic and ecological patterns

Wood anatomy of Buddleja is well-explored but not in many southern African members, which form a grade of species and small clades that form successive sister groups to the rest of the genus, and its bark structure has not been studied at all. We provide new descriptions of wood anatomy for twelve species, including nearly all Buddleja from southern Africa and two species of Freylinia in the sister group of Buddleja. We also describe bark structure from fifteen species. To assess if wood anatomy provides phylogenetic and/or ecological signal, we compiled data on wood traits and climatic variables from the distributions of 53 species. Wood traits counteracting cavitation correlated with higher temperature and precipitation seasonality; simultaneously they were better expressed in species with smaller maximal plant height. It is likely that hotter and drier areas harbour smaller plants which have traits conveying higher conductance safety. Bark structure varies considerably. In bark of Buddleja section Gomphostigma, periderm is initiated in the outer cortex and develops thin-walled phellem, and sclerification of their phloem does not occur. This resembles bark in Freylinia, supporting the position of section Gomphostigma as sister to the rest of Buddleja. In the remaining Buddleja species, bark is characterised by formation of periderm with phelloid cells in the secondary phloem. The phellem is often uniseriate, a condition not reported elsewhere. Its formation occurs close in time to solid sclerification of the cut-off phloem, suggesting a possible novel ontogenetic mechanism.