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Pedogenic thresholds describe where soil properties or processes change in an abrupt/nonlinear fashion in response to small changes in environmental forcing. Contrastingly, soil process domains refer to the space between thresholds where soil properties are either unchanged, or change gradually, across a broad range of environmental forcing. Here, we test quantitatively for the presence of thresholds in patterns of soil properties across a climatic gradient on soils developed from about 20-ky-old basaltic substrate on the Island of Hawai’i. From multiple soil properties, we quantitatively identified a threshold at about 750 mm/y of water balance (precipitation minus potential evapotranspiration), delineating the upper water balance boundary of soil fertility in these soils. From the threshold in the ratio of exchangeable Ca to total Ca, we identified the lower water balance boundary of soil fertility in these soils at – 1000 mm/y; however, this threshold was qualitatively described as it lies near the limit of the climate gradient data where the statistical approach cannot be applied. These two results represent the first time that pedogenic thresholds have been identified using statistically rigorous methods and the limitations of said methods, respectively. Comparing the 20-ky soils to soils that developed on basaltic substrates of 1.2 ky, 7.5 ky, 150 ky, and 4100 ky in a time–climate matrix, we found that our quantitative analysis supports previous qualitatively identified thresholds in the soils developed from older substrates. We also identified the 20 ky as the transition from kinetic to supply limitation for plant nutrients in soil in this system.

Chilean volcanic soils contain large amounts of total and organic phosphorus, but P availability is low. Phosphobacteria [phytate-mineralizing bacteria (PMB) and phosphate-solubilizing bacteria (PSB)] were isolated from the rhizosphere of perennial ryegrass (Lolium perenne), white clover (Trifolium repens), wheat (Triticum aestivum), oat (Avena sativa), and yellow lupin (Lupinus luteus) growing in volcanic soil. Six phosphobacteria were selected, based on their capacity to utilize both Na-phytate and Ca-phosphate on agar media (denoted as PMPSB), and characterized. The capacity of selected PMPSB to release inorganic P (Pi) from Na-phytate in broth was also assayed. The results showed that from 300 colonies randomly chosen on Luria-Bertani agar, phosphobacteria represented from 44% to 54% in perennial ryegrass, white clover, oat, and wheat rhizospheres. In contrast, phosphobacteria represented only 17% of colonies chosen from yellow lupin rhizosphere. This study also revealed that pasture plants (perennial ryegrass and white clover) have predominantly PMB in their rhizosphere, whereas PSB dominated in the rhizosphere of crops (oat and wheat). Selected PMPSB were genetically characterized as Pseudomonas, Enterobacter, and Pantoea; all showed the production of phosphoric hydrolases (alkaline phosphatase, acid phosphatase, and naphthol phosphohydrolase). Assays with PMPSB resulted in a higher Pi liberation compared with uninoculated controls and revealed also that the addition of glucose influenced the Pi-liberation capacity of some of the PMPSB assayed.

This paper attempts to realize the identification and classification of slope failure/landslide patterns in the early warning system (EWS) based on Soil Water Index (SWI), for fuzzy evaluation of the slope failure scale based on meteorological data. For this purpose, the stability analysis and shear strength parametric discussions of a homogeneous slope model composed of two kinds of soil, i.e., volcanic soil and Toyoura sand, are performed under 22 kinds of designed rainfall conditions. In a total of 8,976 simulated slope stability scenarios, 374 slope failures with a factor of safety (FOS) less than 1.0 for the first time were identified. After that, the depths of the potential slip surface of the slope failure patterns were collected and analyzed. Results indicate that the SWI-based EWS can identify and classify the four landslide patterns. As rainfall intensity rises, the slope failure pattern gradually changes from Pattern I (Sliding) during long-term low-intensity (LL) type rainfall, to Pattern II (Buckling), to Pattern III (Toppling), and finally to Pattern IV (Crumbling) during short-term high-intensity (SH) type rainfall. In addition, the correlation between the slope failure pattern and the potential slip depth and SWI is very poor, but there is a strong correlation between the landslide pattern and the potential slip depth and water storage height ( H 2 ) in the second tank layer. Therefore, in the SWI-based EWS, the water storage height ( H 2 ) in the second tank layer might be used to evaluate the scale of slope failure.

Volcanic ash soils retain the largest and most persistent soil carbon pools of any ecosystem. However, the mechanisms governing soil carbon accumulation and weathering during initial phases of ecosystem development are not well understood. We examined soil organic matter dynamics and soil development across a high-altitude (3,560-3,030 m) 20-kyr climate gradient on Mauna Kea in Hawaii. Four elevation sites were selected (~250-500 mm rainfall), which range from sparsely vegetated to sites that contain a mix of shrubs and grasses. At each site, two or three pits were dug and major diagnostic horizons down to bedrock (intact lava) were sampled. Soils were analyzed for particle size, organic C and N, soil pH, exchangeable cations, base saturation, NaF pH, phosphorous sorption, and major elements. Mass loss and pedogenic metal accumulation (hydroxlamine Fe, Al, and Si extractions) were used to measure extent of weathering, leaching, changes in soil mineralogy and carbon accumulation. Reactivephase (SRO) minerals show a general trend of increasing abundance with increasing rainfall. However carbon accumulation patterns across the climate gradient are largely decoupled from these trends. The results suggest that after 20 kyr, pedogenic processes have altered the nature and composition of the volcanic ash such that it is capable of retaining soil C even where organic acid influences from plant material and leaching from rainfall are severely limited. Carbon storage comparisons with lower-elevation soils on Mauna Kea and other moist mesic (2,500 mm rainfall) sites on Hawaii suggest that these soils have reached only between 1% and 15% of their capacity to retain carbon. Our results suggest that, after 20 kyr in low rainfall and a cold climate, weathering was decoupled from soil carbon accumulation patterns and the associated influence of vegetation on soil development. Overall, we conclude that the rate of carbon supply to the subsoil (driven by coupling of rainfall above ground plant production) is a governing factor of forms and amount of soil organic matter accumulation, while soil mineralogy remained relatively uniform.

Effects of global warming on soil organic carbon (C) can be investigated by comparing sites experiencing different temperatures. However, observations can be affected by covariance of temperature with other environmental properties. Here, we studied a thermal gradient in forest soils derived from volcanic materials on Mount Taranaki (New Zealand) to disentangle the effects of temperature and reactive minerals on soil organic C quantity and composition. We collected soils at four depths and four elevations with mean annual temperatures ranging from 7.3 to 10.5 °C. Soil C stocks were not significantly different across sites (average 162 MgC ha−1 to 85 cm depth, P > .05). Neither aluminium (Al)-complexed C, nor mineral-associated C changed significantly (P > .05) with temperature. The molecular characterisation of soil organic matter showed that plant-derived C declined with increasing temperature, while microbial-processed C increased. Accompanying these changes, soil short-range order (SRO) constituents (including allophane) generally increased with temperature. Results from structural equation modelling revealed that, although a warmer temperature tended to accelerate soil organic C decomposition as inferred from molecular fingerprints, it also exerted a positive effect on soil total C presumably by enhancing plant C input. Despite a close linkage between mineral-associated C and soil organic C, the increased abundance of reactive minerals at 30–85 cm depth with temperature did not increase soil organic C concentration at that depth. We therefore propose that fresh C inputs, rather than reactive minerals, mediate soil C responses to temperature across the thermal gradient of volcanic soils under humid-temperate climatic conditions.

The Aeolian archipelago is known worldwide for its volcanic activity and hydrothermal emissions, of mainly carbon dioxide and hydrogen sulfide. Hydrogen, methane, and carbon monoxide are minor components of these emissions which together can feed large quantities of bacteria and archaea that do contribute to the removal of these notorious greenhouse gases. Here we analyzed the metagenome of samples taken from the Levante bay on Vulcano Island, Italy. Using a gene-centric approach, the hydrothermal vent community appeared to be dominated by Proteobacteria , and Sulfurimonas was the most abundant genus. Metabolic reconstructions highlight a prominent role of formaldehyde oxidation and the reverse TCA cycle in carbon fixation. [NiFe]-hydrogenases seemed to constitute the preferred strategy to oxidize H 2 , indicating that besides H 2 S, H 2 could be an essential electron donor in this system. Moreover, the sulfur cycle analysis showed a high abundance and diversity of sulfate reduction genes underpinning the H 2 S production. This study covers the diversity and metabolic potential of the microbial soil community in Levante bay and adds to our understanding of the biogeochemistry of volcanic ecosystems.

As the global greenhouse effect intensifies, the emission and balance of greenhouse gases, particularly carbon dioxide (CO 2 ), have become crucial for achieving global carbon neutrality. Volcanic geothermal regions, as major natural sources of carbon emissions, release substantial volume of greenhouse gases into the atmosphere in various ways including volcanic eruptions, soil microseepages, vents, and hot springs. Among these, soil microseepages are particularly important due to their widespread and persistent nature. However, the geochemical dynamics of CO 2 release from soil microseepage in volcanic regions remain poorly understood. In this study, we propose a novel CO 2 release model employing computational fluid dynamics (CFD) to model CO 2 emissions from soil microseepage in volcanic regions. Our results provide important insights as follows: (1) Low porosity in subsurface strata inhibits CO 2 penetration, while well-developed underground cracks and channels enhance release rates. (2) Favorable gas pathways enable CO 2 to penetrate dense layers, and migrate upward, with migration patterns influenced by gas source pressure, temperature, and soil permeability. Slowing vertical migration increases horizontal diffusion and expands the effective surface release area. (3) Surface release is also influenced by external factors like wind speed, though these do not significantly affect underground seepage. (4) To improve the accuracy of CO 2 flux measurements using the closed chamber method, it is recommended to reverse the initial slope of the CO 2 concentration-time curve. This study provides critical data to enhance global carbon budget assessments and support efforts towards carbon neutrality.

This study examined the frequency-size distribution of 6117 landslides spread over 440 km2 in Iburi Subprefecture, Hokkaido, Japan, induced by the Hokkaido Eastern Iburi Earthquake (Mw 6.6) on September 6, 2018. The study area is characterized by gently undulating terrain that is finely dissected by shallow streams and covered predominantly by layers of volcanic products with high water content. Most of the landslides were shallow landslides, and their slip surfaces often formed in a layer of volcanic soil called the “Ta-d,” deposited at 9000 ybp. Low ridges separating small catchments allowed individual landslides to coalesce in many locations. The average size of landslides was 7160 m2. Landslide size tended to increase with slope angle up to 20° to 25° and then decrease with further increase of slope angle. About half of the landslides occurred in a feature with both concave planform and profile curvature, and their average size was 8720 m2. In contrast, 17% of the total landslides occurred in the case of both curvatures being convex, and their average size was 5190 m2. The results indicated that the accumulation of saturated soil in concave features provided more opportunities for landslides of large sizes. The frequency-size distribution of the landslides presented high rollover, 5.0 × 10−3 km2, but the exponent of power law decay for medium to large landslides, − 2.46, was not largely different from those of studies in other locations. Compared with other seismically caused examples, the landslides triggered by the Hokkaido Eastern Iburi Earthquake can be characterized as more clustered, more numerous, and larger in size for the moment magnitude of the earthquake. Conversely, the magnitude scale for the landslide event estimated from the total landslide area was equivalent to that of a region struck by an earthquake of Mw = 7.0 to 7.4. This study demonstrated that gently undulating regions can produce unexpectedly large and frequent landslides when struck by an intense earthquake, and when soil layers vulnerable to ground shaking cover the ground.

Proteaceae species in south‐western Australia thrive on phosphorus‐impoverished soils, employing a phosphorus‐mining strategy involving carboxylate‐releasing cluster roots. Some develop symptoms of phosphorus toxicity at slightly elevated soil phosphorus concentrations, due to their low capacity to down‐regulate phosphorus uptake. In contrast, Proteaceae species in Chile, e.g. Embothrium coccineum J.R. Forst. & G. Forst., occur on volcanic soils, which contain high levels of total phosphorus, but phosphorus availability is low. We hypothesised that the functioning of cluster roots of E. coccineum differs from that of south‐western Australian Proteaceae species, in accordance with the difference in soil phosphorus status. With more phosphorus to be gained from the soil with high levels of total phosphorus, we expect less investment in biomass and more release of carboxylates. Furthermore, we hypothesised that E. coccineum regulates its phosphorus‐uptake capacity, avoiding phosphorus toxicity when grown at elevated phosphorus levels. To test these hypotheses, E. coccineum seedlings were grown at a range of phosphorus supplies in nutrient solution. We show that E. coccineum allocated at least five times less biomass to cluster roots that released at least nine times more carboxylates per unit cluster root weight compared with south‐western Australian species (e.g. Banksia, Hakea). The highest phosphorus supply caused a growth inhibition and high leaf phosphorus concentration, without symptoms of phosphorus toxicity. We accept our hypotheses on the functioning of cluster roots and the high capacity to reduce the net phosphorus uptake in plants grown at a high‐phosphorus supply. This novel combination of traits indicates divergent functioning of Proteaceae species from southern South America, exposed to frequent phosphorus input due to volcanic activity, in contrast with the functioning of south‐western Australian Proteaceae species that thrive on severely phosphorus‐impoverished soils. These traits could explain the functioning of E. coccineum on soils that are rich in total phosphorus, but with a low concentration of available phosphorus.

The Somma–Vesuvius volcanic complex emitted huge quantities of volcanic materials over a period from before 18,300 years BP to 1944. The activity during the last period, from post-AD 1631 to 1944, primarily produced lava and pyroclastics via effusive and strombolian eruptions. We investigated the pedogenesis on rocks formed from post-AD 1631 to 1944, occurring on the slopes of Mt. Vesuvius up to Gran Cono Vesuviano and in the northern valley separating Vesuvius from the older Mt. Somma edifice. Pertinent morphological, physical, chemical, and mineralogical (XRD and FT-IR) soil properties were studied. The results indicated the existence of thin and deep stratified soils on lava, as well as the presence of loose detritic covers formed via pyroclastic emplacement and redistribution. The soils showed minimal profile differentiation, frequently with layering recording the episodic addition of sediments. We found that the dominant coarse size of primary mineral particles was preserved, and there was a low level of clay production. The main mineralogical assemblage present in sands also persisted in clays, indicating the physical breaking of the parent material. Chemical weathering produced mineral modifications towards the active forms of Al and Fe and was also attested in selected soils by glass alteration, allophane production, and the presence of analcime in clay as a secondary product from leucite. The differences in glass alteration and analcime production found in the selected soils on lava were related to soil particle size and soil thickness. Concerning the youngest soil present on Gran Cono Vesuviano, other factors, such as the substratum’s age and site elevation, appeared to be implicated.