Adjacent Substrates Research Articles

In situ self-assembled near-infrared phototherapeutic agent: unleashing hydrogen free radicals and coupling with NADPH oxidation.

Investigation of electron transfer (ET) between photosensitizers (PSs) and adjacent substrates in hypoxic tumors is integral to highly efficient tumor therapy. Herein, the oxygen-independent ET pathway to generate hydrogen free radicals (H˙) was established by the in situ self-assembled phototherapeutic agent d-ST under near-infrared (NIR)-light irradiation, coupled with the oxidation of reduced coenzyme NADPH, which induced ferroptosis and effectively elevated the therapeutic performance in hypoxic tumors. The higher surface energy and longer exciton lifetimes of the fine crystalline d-ST nanofibers were conducive to improving ET efficiency. In hypoxic conditions, the excited d-ST can effectively transfer electrons to water to yield H˙, during which the overexpressed NADPH with rich electrons can power the electron flow to facilitate the generation of H˙, accompanied by NADP+ formation, disrupting cellular homeostasis and triggering ferroptosis. Tumor-bearing mouse models further showed that d-ST accomplished excellent phototherapy efficacy. This work sheds light onto the versatile electron pathways between PSs and biological substrates.

Predicting encapsulant delamination in photovoltaic modules bridging photochemical reaction kinetics and fracture mechanics

AbstractPhotovoltaic (PV) modules are subjected to environmental stressors (UV exposure, temperature, and humidity) that cause degradation within the encapsulant and its interfaces with adjacent glass and cell substrates. To save experimental time and to enable long‐term assessment with intensive degradation only taking place after many years, the development of predictive models is indispensable. Previous works have modeled the delamination of the ethylene vinyl acetate (EVA) encapsulant/glass and encapsulant/cell interfaces under field aging conditions with fundamental photochemical degradation reactions that lead to molecular scission and loss of interfacial adhesion, characterized by the fracture resistance, Gc. However, these models were fundamentally limited in that the following aspects were not incorporated: (i) molecular crosslinking in the field, (ii) synergistic autocatalytic interactions of degradation mechanisms, (iii) connection between degraded encapsulant structure and its mechanical properties, and (iv) rigorous treatment of the plasticity contribution to Gc with finite element models. Here, we present a time‐dependent multiscale model that addresses these limitations and is applicable to a wide range of encapsulants and interfaces. For the reference EVA encapsulant and its interfaces with the glass and cell, the presented model predicts an initial rise in Gc in the first 3 years of field aging from crosslinking, then a subsequent sharp decline from degradation mechanisms. We used nanoindentation to measure the changes in EVA mechanical properties over exposure time to tune the model parameters. The model predictions of Gc and mechanical properties match with experimental data and show an improvement compared to previous models. The model can even predict switches in failure interfaces, such as the observed EVA/cell to EVA/glass transition. We also conducted a sensitivity analysis study by varying the degradation and crosslinking kinetic parameters to demonstrate their effects on Gc. Model extensions to polyolefin elastomer‐ and silicone‐encapsulants and their interfaces are also demonstrated.

Asymmetric Hydrogenation of Tetrapyridine‐Type N‐Heteroarenes Using Phosphine‐Free Ruthenium Diamine Catalysts†

Comprehensive SummaryChiral ruthenium‐catalyzed enantioselective hydrogenation of tetrapyridine‐type N‐heteroarenes was firstly developed. The partial reduction of adjacent tetraheteroaromatic substrates proceeded smoothly in the presence of phosphine‐free chiral cationic ruthenium diamine complexes, affording unprecedented high reactivity, enantioselecitivity and diastereoselectivity (up to 93% yield, >99% ee and 92 : 8 dr). The potential application of chiral tetradentate pyridine‐amine products as chiral ligands has been demonstrated in the Cu‐catalyzed asymmetric Friedel–Crafts alkylation reaction between indoles and nitroalkenes.

Multi-scale remote sensing-based landscape epidemiology of the spread of rapid ‘Ōhiʻa Death in Hawaiʻi

Fungal pathogens of the genus Ceratocystis recently introduced to the Island of Hawaiʻi have killed hundreds of thousands of native ‘Ōhiʻa trees, an ecologically and culturally important keystone species. Symptoms of the associated disease, Rapid ‘Ōhiʻa Death (ROD), have been found to be easily detectable with high resolution imaging spectroscopy. We used wall-to-wall maps of affected ‘Ōhiʻa canopy built in four consecutive years (2016–2019) to analyze how changes in the distribution and density of browning canopy detections over this time period corresponded to environmental drivers at two spatial scales. Island-wide we found 256,387 brown crowns across the 4-year period. The total amount of affected forest area nearly doubled from 66,972.2 ha in 2016 to 121,464.7 ha in 2019, cumulatively representing 42.5% of the 264,372 ha of forest area observed at least once in the study. However, most browning activity was concentrated in 18 hotspots totaling approximately 29,836 ha with brown crown densities as high as 26 ha−1. Using Random Forest (RF) models, we assessed the correspondence between 32 mapped environmental variables and measures of ROD spread calulated at 1-year time steps on a 300 m × 300 m grid across the island. We found that modelled probability of regional infection, or “susceptibility”, was dominated by distance to existing infection at the start of a time step; increasing distance from 0 to 600 m decreased susceptibility from 0.8 to 0.3. Other important factors – tree cover, average windspeeds, and LiDAR-derived 3-d crown exposure – were 4–10 times less important to the model. In a second RF model we studied regional infection “severity”, measured as detection density in first year of infection. In contrast to susceptibility, the severity model was significantly affected by numerous factors including windspeed metrics, canopy height and exposure as well as most weather and climate metrics related to water regime. Severity model predictions were less dominated by proximity to existing infection. In a separate regional analysis at 2 m resolution we found that taller trees were more prone to infection, and that trees on younger “historic” lava flows (i.e., substrates < 230 years old) showed slight but significantly lower infection rates than immediately adjacent older substrates. Our results document the extent and severity of ‘Ōhiʻa mortality across Hawaiʻi Island and provides insight into factors that appear to affect the spread of ROD; this information will inform management efforts to lessen the spread and impact of the disease on all the Hawaiian Islands.

Two-beam interferometry with a definitive phase-shift sign

Subject of study. The shift direction of interference fringes depending on the sign of the local phase shift introduced to one of the interfering waves was investigated in terms of two-beam interferometry. Aim of study. This study aimed to validate the fact that two-beam interferometry based on a single interferogram enables definitive determination of the phase-shift sign using the shift direction of the interference fringe. Method. Positions of the interference fringes and their shifts were calculated considering the phase distribution of interfering waves in the observation plane. The Mach–Zehnder interferometer was used to experimentally confirm the obtained theoretical results. Two closely adjacent substrates were used as objects. A subwavelength layer of a standard material was deposited on a part of the surface of one substrate, and a layer of metamaterial was deposited on the part of the second substrate. Main results. Expressions determining the direction and amplitude of the shift of interference fringes depending on the sign and amplitude of the local phase shift in one of the two interfering waves with a plane or spherical front were obtained. Strict rules of interference fringe shift depending on the sign of the phase shift were formulated based on the calculations. Results of the experiment using the Mach–Zehnder interferometer with different combinations of beams with spherical and plane wavefronts confirmed the theoretical calculations. Practical significance. Classic interferometric methods require significant time and the application of complex experimental procedures to determine the sign of the phase shift. The application of the results obtained in this study enables the determination of the sign of the introduced local phase shift based on a single interferogram without additional time expenditures. Thus, the method investigating the metamaterial layers of a subwavelength thickness is significantly simplified.

Fungal Hyphosphere Microbiomes Are Distinct from Surrounding Substrates and Show Consistent Association Patterns.

Mat-forming fungi are common in forest and grassland soils across the world, where their activity contributes to important soil ecological processes. These fungi maintain dominance through aggressive and abundant hyphae that modify their internal physical and chemical environments and through these modifications select for what appears to be a suite of mycophilic bacteria. Here, the bacteria associated with the fungal mats of Leucopaxillus gentianeus and Leucopaxillus albissimus from western North America are compared to adjacent nonmat substrates. Within the mats, the bacterial richness and diversity were significantly reduced, and the community composition was significantly different. The bacterial community structure between the two fungal hosts was marginally significant and indicated a shared set of bacterial associates. The genera Burkholderia, Streptomyces, Bacillus, Paenibacillus, and Mycobacterium were significantly abundant within the fungal mats and represent core members of these hypha-rich environments. Comparison with the literature from fungal mat studies worldwide showed that these genera are common and often significantly found within fungal mats, further reinforcing the concept of a mycophilic bacterial guild. These genera are incorporated into a synthesis discussion in the context of our current understanding of the nature of fungal-bacterial interactions and the potential outcomes of these interactions in soil nutrient cycling, plant productivity, and human health. IMPORTANCE Fungi and bacteria are the most abundant and diverse organisms in soils (perhaps more so than any other habitat on earth), and together these microorganisms contribute to broad soil ecosystem processes. There is a suite of bacteria that appears consistently within the physical space called the hyphosphere, the area of influence surrounding fungal hyphae. How these bacteria are selected for, how they are maintained, and what broader ecological functions they perform are subjects of interest in this relatively new field-the cross-kingdom interactions between fungi and bacteria. Understanding their cooccurrence and their interactions can open new realms of understanding in soil ecological processes with global consequences.

A highly-efficient 3D DNAzyme motor for sensitive biosensing analysis

Herein, driven by the need of highly-efficient DNAzyme-amplified detection strategy, a novel 3D DNAzyme motor was designed as a biosensor platform for realizing sensitive detection of target DNA. The 3D DNAzyme motor was composed of target-activated DNAzyme nanowires and substrates H1-Fc that co-immobilized on Au@Fe3O4 nanoparticles (Au@Fe3O4NPS) surface, possessing high local concentration of DNA reactants and shortened distance between DNAzyme and substrates for enhancing electrochemical signal. Compared with traditional DNAzyme-powered machines, the target-activated DNAzyme nanowires of 3D DNAzyme motor had greater flexibility and more powerful cleavage capability without troublesome sequence optimization, which overcame the space limitation and simultaneously interacted with adjacent and distant substrates H1-Fc to output a large amount of cleavage products with high signal response. Therefore, on account of the above-mentioned merits of nanoparticles localization DNA design and DNAzyme nanowires, the reported 3D DNAzyme motor ingeniously overcame many defects existing in traditional DNAzyme-amplified detection strategies such as low reactants concentration, limited flexibility of DNAzyme and small DNAzyme swing range, realizing the sensitive detection of target DNA with a detection limit of 1.7 fM ranging from 5 fM to 50 nM. Impressively, the 3D DNAzyme motor here presented a new strategy to achieve effective DNAzyme signal amplification and provided a reference for the assembly of various and functional 3D DNA machines in the future.

Supramolecular Template-Assisted Catalytic [2+2] Photocycloaddition in Homogeneous Solution

Supramolecular Template-Assisted Catalytic [2+2] Photocycloaddition in Homogeneous Solution

First steps towards interlocking modular microfluidic cooling substrates (i-MμCS) for future silicon tracking detectors in High Energy Physics (HEP)

In future High Energy Physics detectors, the coverage of large surfaces with silicon pixel chip sensors poses a challenge for the sensors positioning, for their cooling, assembly, and interconnection. The use of a cooling substrate on which the sensors are glued is typically limited by the bulky and complicated hydraulic interconnection between adjacent substrates. In this research, a new type of cooling substrate is presented. Its design is based on microchannels, where additive manufacturing of plastic and ceramic materials has been considered an alternative to the current silicon etching process. A solution to the mechanical and hydraulic interconnection problem is achieved through a modular interlocking concept. Design optimisation was followed having identified three relevant parameters, plug-and-ply, interchangeability and sealing performance, which qualify the substrates interconnection and guaranty their correct positioning. This paper poses the bases to a new substrate category where modularity, re-workability and easy connectivity are the strong points. This concept could find applications also outside High Energy Physics experiments such as hardware cloud computing and medical detectors.

Emerging Designs of Aggregation-Induced Emission Agents for Enhanced Phototherapy Applications

Emerging Designs of Aggregation-Induced Emission Agents for Enhanced Phototherapy Applications

Nanosheet array-like Cu@Cu2O-CuNiAl(O)/rGO composites for highly efficient reduction of nitrophenol: Electronic and structure promotion effect of nickel

Series of hierarchical nanosheet array-like composites xCu@Cu2O-CuNiAl(O)/rGO (x = 1.0, 1.5, 2.0) were constructed via proper calcination of pre-prepared hybrids CuxNi3-xAl-layered double hydroxide/rGO in N2 flow, upon the LDH layer atomic-level lattice confined in situ self-reduction for Cu2+ ions by rGO substrate along with the dispersion effect of Ni-OH groups. Systematic characterizations reveal that core@shell-type Cu@Cu2O nanoparticles (NPs) are definitely trapped in the border space among the vertically adjacent CuNiAl(O) nanosheets and rGO substrates. All the xCu@Cu2O-CuNiAl(O)/rGO composites exhibit excellent catalytic activities for the reduction of 4-nitrophenol (4-NP), particularly 1.5Cu@Cu2O-CuNiAl(O)/rGO possesses the highest activity (kapp: 7.6 × 10-2 s−1, TOF: 265.0 h−1), and superb reusability with insignificant loss in activity for continuous 25 cycles, much better than those of recently reported Cu-based catalysts and even comparable to some noble metal catalysts. The best performance of 1.5Cu@Cu2O-CuNiAl(O)/rGO can be mainly attributed to the most uniformly dispersed electrophilic core@shell Cu@Cu2O NPs modified by NiO species structurally and electronically, the strongest Cu–Cu2O–CuNiAl(O)–rGO synergistic effect upon the unique nanosheet array-like morphology providing more ion-accessible active sites, and much improved adsorption for 4-NP via rGO layer due to π-π stacking. The universality and fixed bed tests further demonstrate potential practical applications of the present hierarchical non-noble composites for water remediation. The present facile synthesis strategy of the nanosheet array-like Cu@Cu2O-CuNiAl(O)/rGO composites with multi-phases synergy may be greatly beneficial to the design and construction of many other highly efficient multi-transition metal-based catalysts with excellent structural robustness for a broad range of applications in related catalysis processes.

Distinct Microbial Communities in Adjacent Rock and Soil Substrates on a High Arctic Polar Desert.

Understanding microbial niche variability in polar regions can provide insights into the adaptive diversification of microbial lineages in extreme environments. Compositions of microbial communities in Arctic soils are well documented but a comprehensive multidomain diversity assessment of rocks remains insufficiently studied. In this study, we obtained two types of rocks (sandstone and limestone) and soils around the rocks in a high Arctic polar desert (Svalbard), and examined the compositions of archaeal, bacterial, fungal, and protistan communities in the rocks and soils. The microbial community structure differed significantly between rocks and soils across all microbial groups at higher taxonomic levels, indicating that Acidobacteria, Gemmatimonadetes, Latescibacteria, Rokubacteria, Leotiomycetes, Pezizomycetes, Mortierellomycetes, Sarcomonadea, and Spirotrichea were more abundant in soils, whereas Cyanobacteria, Deinococcus-Thermus, FBP, Lecanoromycetes, Eurotiomycetes, Trebouxiophyceae, and Ulvophyceae were more abundant in rocks. Interestingly, fungal communities differed markedly between two different rock types, which is likely to be ascribed to the predominance of distinct lichen-forming fungal taxa (Verrucariales in limestone, and Lecanorales in sandstone). This suggests that the physical or chemical properties of rocks could be a major determinant in the successful establishment of lichens in lithic environments. Furthermore, the biotic interactions among microorganisms based on co-occurrence network analysis revealed that Polyblastia and Verrucaria in limestone, and Atla, Porpidia, and Candelariella in sandstone play an important role as keystone taxa in the lithic communities. Our study shows that even in niches with the same climate regime and proximity to each other, heterogeneity of edaphic and lithic niches can affect microbial community assembly, which could be helpful in comprehensively understanding the effects of niche on microbial assembly in Arctic terrestrial ecosystems.

The bZIP Proteins of Oncogenic Viruses.

Basic leucine zipper (bZIP) transcription factors (TFs) govern diverse cellular processes and cell fate decisions. The hallmark of the leucine zipper domain is the heptad repeat, with leucine residues at every seventh position in the domain. These leucine residues enable homo- and heterodimerization between ZIP domain α-helices, generating coiled-coil structures that stabilize interactions between adjacent DNA-binding domains and target DNA substrates. Several cancer-causing viruses encode viral bZIP TFs, including human T-cell leukemia virus (HTLV), hepatitis C virus (HCV) and the herpesviruses Marek’s disease virus (MDV), Epstein–Barr virus (EBV) and Kaposi’s sarcoma-associated herpesvirus (KSHV). Here, we provide a comprehensive review of these viral bZIP TFs and their impact on viral replication, host cell responses and cell fate.

Warm seawater temperature promotes substrate colonization by the blue coral, Heliopora coerulea.

BackgroundHeliopora coerulea, the blue coral, is a reef building octocoral that is reported to have a higher optimum temperature for growth compared to most scleractinian corals. This octocoral has been observed to grow over both live and dead scleractinians and to dominate certain reefs in the Indo-Pacific region. The molecular mechanisms underlying the ability of H. coerulea to tolerate warmer seawater temperatures and to effectively compete for space on the substrate remain to be elucidated.MethodsIn this study, we subjected H. coerulea colonies to various temperatures for up to 3 weeks. The growth and photosynthetic efficiency rates of the coral colonies were measured. We then conducted pairwise comparisons of gene expression among the different coral tissue regions to identify genes and pathways that are expressed under different temperature conditions.ResultsA horizontal growth rate of 1.13 ± 0.25 mm per week was observed for corals subjected to 28 or 31 °C. This growth rate was significantly higher compared to corals exposed at 26 °C. This new growth was characterized by the extension of whitish tissue at the edges of the colony and was enriched for a matrix metallopeptidase, a calcium and integrin binding protein, and other transcripts with unknown function. Tissues at the growth margin and the adjacent calcified encrusting region were enriched for transcripts related to proline and riboflavin metabolism, nitrogen utilization, and organic cation transport. The calcified digitate regions, on the other hand, were enriched for transcripts encoding proteins involved in cell-matrix adhesion, translation, receptor-mediated endocytosis, photosynthesis, and ion transport. Functions related to lipid biosynthesis, extracellular matrix formation, cell migration, and oxidation-reduction processes were enriched at the growth margin in corals subjected for 3 weeks to 28 or 31 °C relative to corals at 26 °C. In the digitate region of the coral, transcripts encoding proteins that protect against oxidative stress, modify cell membrane composition, and mediate intercellular signaling pathways were enriched after just 24 h of exposure to 31 °C compared to corals at 28 °C. The overall downregulation of gene expression observed after 3 weeks of sustained exposure to 31 °C is likely compensated by symbiont metabolism.DiscussionThese findings reveal that the different regions of H. coerulea have variable gene expression profiles and responses to temperature variation. Under warmer conditions, the blue coral invests cellular resources toward extracellular matrix formation and cellular migration at the colony margins, which may promote rapid tissue growth and extension. This mechanism enables the coral to colonize adjacent reef substrates and successfully overgrow slower growing scleractinian corals that may already be more vulnerable to warming ocean waters.

Megabenthic assemblages at the southern Central Indian Ridge – Spatial segregation of inactive hydrothermal vents from active-, periphery- and non-vent sites

Active hydrothermal vents are small-scale habitats hosting endemic fauna in a well-defined zonation around fluid effluents. The fauna of inactive hydrothermal vents and its relation to active vents and non-vent area is poorly known. Characterizing inactive areas is prerequisite to establish protected areas, especially in the context of potential seafloor massive sulfide mining, which targets inactive sites. Hierarchical clustering and Distance-based Redundancy Analysis revealed five assemblages, with significantly associated substrate types: I) active hydrothermal vent, II) periphery, III) inactive hydrothermal vent and IV) soft- and V) hard-substrate within the non-vent area. For the first time, a unique inactive faunal assemblage could be identified within the hydrothermally extinct inactive Gauss field and on adjacent hard substrates. The spatial separation from the active Edmond field and periphery and the non-vent area indicates the existence of an inactive assemblage.

Macrofaunal biodiversity associated with different developmental phases of a threatened Mediterranean Sabellaria alveolata (Linnaeus, 1767) reef

Sabellaria alveolata is an ecosystem engineer species capable of building bioconstructions, playing a key functional role in the shallow coastal ecosystems. S. alveolata reefs perform several ecosystem services, such as hosting a rich fauna and producing structures able to provide coastal protection. Despite their ecological role, these bioconstructions have been poorly investigated in the Mediterranean Sea. In this study, the largest Mediterranean S. alveolata reef, located along the Latium coast, was recorded and an habitat mapping duly carried out. During a one-year study, the balance between reef status and associated fauna was investigated using a multidisciplinary approach, the different phases in the annual cycle of S. alveolata were detected and the reef's influence on the diversity of associated macrofauna was assessed. The retrograding phase was detected in September, due to the damages by trampling disturbance, while the growing phase began in March. The comparison with the fauna of the adjacent substrates was also performed, demonstrating that the reef supported a high diversity of associated fauna and qualifying the reef as a biodiversity hotspot.Aimed at improving knowledge of Mediterranean reefs, our study lays the basis for more effective management plans and protection strategies for the threatened biogenic habitats.

High-Gain Circularly Polarized Fabry–Pérot Patch Array Antenna With Wideband Low-Radar-Cross-Section Property

In this paper, we explore the adoption of a chessboard polarization conversion metasurface (CPCM) for constructing a low-radar-cross-section (RCS), high-gain circularly polarized patch array antenna. The proposed CPCM is used as the CPCMs’ chessboard configuration, which consists of adjacent two-layer substrates that have three metallic models. Low RCS is achieved by 180° (± 30°) reflection phase variations of two adjoining PCMSs. Gain enhancement is achieved by adopting a Fabry–Perot cavity constituted by a PCM and the antenna’s ground. The antenna with a CPCM that operates at X-/Ku-band, excited by the feeding network that is rotated sequentially, is measured and fabricated. The patch array antenna impedance bandwidth based on the PCM was measured as 3.3 GHz (9.5–12.8 GHz) with a 3-dB axial ratio bandwidth of 11.6% and a high gain of 13.4 dBiC (9.5–12 GHz), more than 2.5 dB higher when compared with a patch antenna without a PCM. In addition, the patch array antenna produced a useful wideband RCS decrease in the operational bandwidth from 9 to 13 GHz.

Building up marine biodiversity loss: Artificial substrates hold lower number and abundance of low occupancy benthic and sessile species

Ocean sprawl is replacing natural substrates with artificial alternatives. We hypothesized that, after submersion, high occupancy, high mobility species colonize artificial substrates faster than low occupancy, low mobility species, a biodiversity divergence that will slowly fade out with time. Using quantitative visual census of species in 10 artificial and their adjacent natural substrates, we tested for the existence and temporal evolution of this divergence. Assigning species to one of three occupancy and one of three mobility categories, we found that artificial substrates increased the performance of high mobility, high occupancy species while decreased the performance of low occupancy species with medium and low mobility. This biodiversity divergence remained unchanged over the 50-year underwater timespan of the artificial substrates investigated. Our results suggest that proliferation of artificial substrates is building up a biodiversity loss driven by the least conspicuous and uncommon benthic and sessile species that is undermining coastal marine biodiversity.

Hot soils and cooler stones: Geoecological influence of volcanic tephra and boulders on soil temperature, and significance for plant distribution in Haleakalā Crater (Maui, Hawai'i)

This project: (i) investigates the geoecological influence of boulders, and their dimensions (thickness, length), on maximum daily soil temperatures beneath them at two sites (2175 and 2685m) in Haleakalā Crater, Maui, (ii) contrasts temperatures in bare volcanic-ash soils with adjacent substrates covered by reddish tephra at 7 study sites (~2170–2735m); these encompass most of the altitudinal range of kūpaoa and silversword, two common plants in this mountain area, and (iii) analyzes effects of tephra depth on soil maxima. Midday soil temperatures were measured with thermocouple thermometers (−5cm); recording thermographs also monitored temperatures continuously in various contrasting substrates for ≤8day periods. Both boulders and tephra substantially decreased soil maxima. Bare-soil highs (n: 100) reached 47.6°C (mean: 37.2±4.4°C). Maxima below boulders (n: 40, 4–109cm thick, 6–265cm long) peaked at 20.5°C (mean: 16.0±2.54°C), whereas 80 readings under tephra (9–95mm depth) reached 32.0°C (mean: 25.2±5.2°C). Larger boulders were most effective in lowering temperatures; Spearman and Kendall correlation tests indicate block thickness was slightly more important (p<0.001) than length in decreasing soil maxima (p<0.005). Deeper tephra layers also effected significant temperature reduction; a polynomial regression shows depth alone accounted for ~92% (p<0.0075) of the temperature differences between bare and tephra-covered ground. Temperature reduction resulted mainly from insulation by stones, but substrate color also exerted some influence on soil temperatures. Volcanic-ash soils were dark—black to dark brown (Munsell 10YR 2/1-3/4 or 7.5YR 3/1-3/4)—whereas tephra fragments were lighter, reddish gray to reddish brown (5YR 4/2-5/4). Lower tephra color values caused greater albedo; higher tephra reflectivity helped reduce absorption of solar radiation, and consequently soils remained cooler below stones. Such temperature reduction is ecologically significant for plant survival on stone-covered areas, as soil maxima ≥35°C may be deleterious to seed and/or seedling survival.

Seedling Regeneration in the Alpine Treeline Ecotone: Comparison of Wood Microsites and Adjacent Soil Substrates

Although climate warming is generally expected to facilitate upward advance of forests, conifer seedling regeneration and survival may be hindered by low substrate moisture, high radiation, and both low and high snow accumulation. To better understand substrate-related factors promoting regeneration in the alpine treeline ecotone, this study compared 2 substrates supporting conifer seedlings: rotten downed wood and adjacent soil. Study locations, each with 3 levels of incoming radiation, were randomly selected at forest line–alpine meadow borders in Pacific Northwest wilderness areas extending along an east–west precipitation gradient. Associations among substrate type, seedling density, radiation, site moisture, site temperature, plant water potential, and plant stomatal conductance were assessed. Wood microsites, flush with the ground and supporting Abies spp conifer seedlings, extended up to 20 m into alpine meadows from the forest line. Although wood microsites thawed later in the spring and froze earlier in the fall, they had warmer summer temperatures, greater volumetric water content, and more growing degree hours, and seedlings growing on wood had higher water potentials than seedlings growing on adjacent soil. At drier eastern sites, there was a positive relationship between seedling density and volumetric water content. Further, there was a positive relationship between seedling stomatal conductance and volumetric water content. Our study indicates that in the Pacific Northwest. and likely elsewhere, seedlings benefit from wood microsites, which provide greater water content. Given predictions of increased summer drought in some locations globally, wood microsites at forest line–alpine meadows and forest line–grasslands borders may become increasingly important for successful conifer regeneration.