Volcanic Substrates Research Articles

Abiotic correlates with diversity and distinctiveness in Sunshine Coast heathlands: Moisture, volcanic landscapes and patterned mounds

AbstractThe ongoing management and protection of conservation areas can be informed by understanding factors that affect the integrity of these communities. Abiotic factors associated with diversity and phylogenetic dispersion within communities, as well as distinctiveness between communities, may potentially be impacted by climate change or changes in hydrology due to urbanization. This study used a range of diversity metrics, along with nominal and quantitative abiotic data, to examine correlates with diversity patterns in the Sunshine Coast heathlands, ecosystems under threat from urban development. Metrics for 80 heathland sites over a variety of substrates, moisture levels and topographic factors were compared using univariate and multivariate statistics. Moisture is a key abiotic factor correlated with the diversity and distinctiveness of heath, and also with higher phylogenetic dispersion of moist and wet sites, indicating possible refuges. Vegetation composition patterns were distinct in the heaths on Tertiary and Triassic rocky volcanic substrates, with the overlapping composition of heath on other substrates, confirming the tolerance of many heath species to a variety of substrates. Patterned natural ‘mounds’ and ‘trenches’ were associated with phylogenetic evenness and are possible refugia. Multivariate analysis had a weak positive correlation of environmental factors with vegetation and phylogenetic composition, emphasizing the complexity of correlates with diversity for the heathlands. This study suggests that both the management of hydrological changes and protection of potential refugial areas are likely to be critical in maintaining the integrity and diversity of the Sunshine Coast heathlands.

Elemental assay of the fumarolic microecology of the Los Azufres (México) volcanic complex using nuclear analytical techniques

The elemental composition of the mantle is a key factor for the understanding of the science of the earth’s interior. However, the direct sampling of the mantle is a difficult and involved task. Fumarolic vapours carry a certain imprint of the mantle composition but are also relatively difficult to sample directly given their high temperature and acidity. Many terrestrial fu- marolic vents are colonized by extremophilic mosses that absorb the vapours and become repositories of the mantle elements brought up by the vapours. The elemental composition of the niche ecology of the fumarole therefore may serve as a near “proxy” for the deep-earth elemental profile of the region. Our study concerns the elemental composition of fumarolic plants, their rhizospheric soil, hydrothermal sediment and volcanic substrate collected from three geothermal microecological sites of the Los Azufres volcanic complex of Mexico. This work presents the results for the heavy elements (HE) Cd, Hg, Pb, Th and U that have been determined using the nuclear analytical techniques of Polarized Energy Dispersive Xray Fluorescence (PEDXRF) spectrometry, Instrumental Neutron Activation Analysis (INAA) as well as Inductively Coupled Plasma Mass spectrometry (ICPMS). The distributions of these HE in the aforesaid biogeochemical matrices are examined and rationalized with respect to possible mechanisms of their deposition. Comparisons with literature reports of the HE composition of fumarolic sulphur deposits and fumarolic vapours of the volcanoes of the Kuril Islands and geothermal aquifers of Iceland, are made. The HE composition is found to vary considerably by the geographic location of the fumarole. However, the trend of the concentrations of these 5 HE is found to be approximately the same for the fumarolic plants of Los Azufres as with the fumarolic vapours of the Kuril volcanoes the displacement being only in the magnitudes. Consequently, the concentrations of these 5 HE in the fumarolic plants are direct qualitative analogues of the vapours of those particular fumaroles of Los Azufres and thereby of the deep-earth geochemistry of that particular geothermal zone.

Soil distribution and soil properties in the subalpine region of Kazbegi, Greater Caucasus, Georgia: Physicochemical properties, distribution and genesis

Due to their characteristic properties, mountain soils require adequate management if used for cropping or grazing, even if climatic conditions are favorable. This study provides a summary of a three-year field campaign that evaluated mountain soils in in northern Georgia for sustainable agricultural use. Soils in the Kazbegi study area, located on the northern slope of the Great Caucasian Ridge, were mapped in 2014 and 2015. The soils developed mainly on sediment fans and on glacial and fluvial sediments. They were characterized by a low to moderate yield potential, with high-yield soils found on volcanic plateaus. Despite the high diversity of terrestrial and semi-terrestrial soils, common to all of them was a high humus content. In the river valleys, Fluvisols (or at least soils with fluvic-properties) were widespread and in the valley depressions fens, e.g., Histosols, occurred as well. On volcanic substrates, medium to very deep Cambisols or Umbrisols were found, with moderate to good agricultural yield potentials. However, P-sorption, mainly on amorphous Al- and Fe-oxides, could lead to an increased need for fertilization. Cambisols were present on moraine, and primarily Regosols and Cambisols on the clay and silt-rich sedimentary rocks of the Jurassic, including a widely distributed coarse fraction. The cambic horizon was not visually apparent but was clearly detectable analytically. Depending on the slope inclination and exposure, even Leptosols occurred on the slopes and peaks of sedimentary or volcanic rocks. Based on these results, a synthetic soil map merging geological and geodetic data as well as data from field mapping was created to provide an instrument for land use management.

Origin of Fe-rich clay minerals in Early Devonian volcanic rocks of the Northern Minusa basin, Eastern Siberia

The formation of clay minerals in volcanic successions follows various evolutionary trends, the understanding of which is crucial for estimating the age of volcanism and the prospecting clay deposits. Early Devonian volcanics within the Byskar Series of the Minusa Depression (Khakassia) are variably altered to a range of phyllosilicate mineral assemblages. This study highlights the origin and formational conditions of the clay minerals, including illite, glauconite, smectite (saponite) and chlorite. Detailed mineralogical and chemical investigation identifies the predominant phyllosilicates, including 1 M illite, illite-smectite (R = 3), 1 M glauconite, smectite, chlorite and kaolinite within trachyandesite, trachyte, and rhyodacite. The phyllosilicates formed by the diagenetic transformation of volcanics after eruptive phases. Evolution trends of phyllosilicates depend largely on the composition of the volcanic substrate. The smectite to illite trend developed due to the dissolution of felsic volcanics and the alteration of smectites into illites with the K+, Al3+ and Mg2+ dominating the mineral formation system. The illites evolved by the substitution of Fe2+ and Mg2+ for Al3+ in the octahedral sheets of smectites. The K+, which was released due to devitrification of felsic substances, was introduced into the interlayer sites for compensating the layer charge originated by the isomorphic substitution in tetrahedral and octahedral sheets. The smectite to glauconite transition trend corresponds to the devitrification and dissolution of alkaline intermediate-felsic volcanics. Early formed dioctahedral smectites evolved into glauconite probably with the predominance of K+ and Fe2+/3+ ions in the formation environment. The substitution of Fe2+/3+ to Al3+ and Mg2+ in the octahedral sheets of smectite contributed to the formation of a layer charge and the entry of exchangeable K+ into the interlayers of glauconite. The third trend involved the formation of smectites (saponites) or chlorites within the intermediate volcanics possibly with Mg-rich but K-poor mineral system.

Distribution of Soil Nutrients and Ancient Agriculture on Young Volcanic Soils of Ta‘ū, American Samoa

Soils and agriculture are inextricably linked, in the past as well as today. The Pacific islands, which often represent organized gradients of the essential soil-forming factors of substrate age and rainfall, represent excellent study systems to understand interactions between people and soils. The relationship between soil characteristics and indigenous agricultural practices are well documented for some locations, but there is a paucity of data for much of the region. Given the extent of ecological adaptation that has been documented, specifically for Hawai‘i, new Pacific datasets are expected to provide important insights into indigenous agricultural practices. To contribute to this discussion, we analyzed patterns in soil chemistry and vegetation in the Manu‘a islands of American Samoa. Soils were sampled along transects that crossed through precontact settlement zones in the upland of Fiti‘uta on Ta‘ū island, a location characterized by young (<100 ky) volcanic substrates and very high (>3800 mm y−1) annual rainfall. Soils were analyzed for several soil fertility properties that have been proposed as predictors of intensive rainfed tuber production in Hawai‘i and Rapa Nui. Surveys of remnant economic plants were conducted to assess patterns of past land use. Soils demonstrated moderate values of soil fertility as measured by pH, base saturation, exchangeable calcium, and total and exchangeable phosphorus, despite the high rainfall. Previously identified soil fertility indicators had some application to the distribution of traditional agriculture, but they also differed in important ways. In particular, low exchangeable calcium in the soils may have limited the agricultural form, especially the cultivation of tubers. Significant shifts in both soil parameters and remnant economic crops were documented, and alignment suggests cropping system adaptation to soil biochemistry. Archaeological samples combined with surveys of relict vegetation suggest that agroforestry and arboriculture were key components of past agricultural practices.

Ecotonic Communities of Diatoms in the Southeastern Part of the Kamchatka Peninsula

Data about the ecotonic diatom communities of the Kamchatka Peninsula, a unique territory with strong volcanic activity, are very limited. We aimed to investigate diatom algae of the ecotones in the southeastern part of Kamchatka, including the Paratunka river valley, at the foot of the Vachkazhets volcano, and the bank of the Bystraya river. In total, 55 taxa were identified. The most diverse were the flora of the Paratunka river, with 31 taxa. Near the Bystraya river, 26 taxa were identified. Near the Vachkazhets volcano, 18 taxa were identified. Fragilariforma virescens, Planothidium lanceolatum, Pinnularia cf. subcapitata, Halamphora normanii, Nitzschia palea, and Eunotia exigua were the dominant species in the studied ecosystems, with the maximum abundance score. Pinnularia cf. subcapitata and Planothidium lanceolatum were found in all ecotones. In the studied habitats, small indifferent alkaliphilic cosmopolitan species prevailed. Our study revealed that the diatom species composition of the Kamchatka ecotones reflects their adaptability to survive in the extreme conditions of volcanic substrates. The results contribute to our knowledge of the ecology and biogeography of a number of diatom taxa.

On the distribution of Ditrichum divaricatum (Ditrichaceae, Bryophyta) in North Pacific region

New data on the distribution of Ditrichum divaricatum Mitt. are presented. This species was described from Japan and previously known also from South Korea and China; it is identified in collections from Russia (Transbaikalia, Suntar-Khayata Mt. Range in Yakutia, and the Kamchatka Peninsula) and from Alaska (USA). Most specimens from Russia were previously attributed to D. pallidum (Hedwig) Hampe but the revision of the herbarium collections in MW, MHA, and LE did not confirm the presence of the latter species in the country. A description and illustrations of D. divaricatum based on Russian specimens are provided as well as data on its ecology; in the north of the Pacific, the species is confined to volcanic substrates of acidic composition.

Climatic Niche, Altitudinal Distribution, and Vegetation Type Preference of the Flea Beetle Genus Arsipoda in New Caledonia (Coleoptera Chrysomelidae)

New Caledonia is one of the major biodiversity hotspots. The flea beetle genus Arsipoda (Coleoptera Chrysomelidae) is present with 21 species, all endemic. We investigated, using GIS analyses and ecological niche models, the habitat preferences of these species in terms of vegetation types, altitude, and climate, and assessed the adequacy of knowledge on the spatial parameters affecting the distribution of the genus in New Caledonia. Altitude and geology seem to play an important role in shaping species distribution. Volcanic substrate allows the growth of ultramafic vegetation, which includes most of their host plants. From a biogeographic and conservation perspective, our results report a deep link between Arsipoda species and their habitats, making them particularly sensitive to environmental modifications.

Volcanic Landforms and Landscapes of the East Carpathians (Romania) and Their Geoheritage Values

The Neogene–Quaternary volcanic range running along the East Carpathians in Romania, extends from the Oaș Mountains, in the north-west, to the South Harghita Mountains and the Perșani Mountains, in the south-east, as part of the broader volcanic province of the Carpathian–Pannonian Region. It resulted from intense volcanic activity during the 15–0.1 Ma time interval, generating huge volumes of effusive and explosive products and a variety of volcanic edifices and primary landforms from large composite volcanoes to small-sized domes/dome-coulées/lava flows and volcaniclastic plateaus around them. The present-day landforms were shaped by various syn-volcanic deformation processes (such as volcano spreading), post-volcanic erosion of various degrees and types (including glacial erosion on the highest-elevation parts and relief inversion in the peripheral areas) and modern anthropic intervention. Developed on this diverse volcanic substrate, the present-day landscape shows a large variety of aspects due to further factors (original topography, elevation, vegetation cover, distance from settlements, anthropic activities, and degradation processes). This volcanic range hosts many geoheritage-relevant sites of various spatial extent (from hundreds of km2 to limited areas of a few 10 m2) and of protection status (from national parks, natural or scientific reserves, natural monuments, and protected areas to areas with no protection at all). Despite its high geoheritage potential, geoparks are still absent, geotrails are sparse, and geotourism is in its infancy in the East Carpathian volcanic range.

Vegetation cover, gross photosynthesis and remotely sensed vegetation indices in different aged sub-arctic volcanic islands in the Vestmannaeyjar archipelago

Surtsey and the older islands in the Vestmannaeyjar archepelago offer a unique possibility to study how subArctic ecosystems develop from unvegetated mineral volcanic substrate to grasslands with thick Brown Andosol soils. The present study was carried out on 24 study plots distributed across six different ecoystems on Surtsey, Heimaey and Elliðaey islands and involved field measurements of soil volumetric water content (VWC), vascular plant cover (VPC) and instantanious rate of gross primary production (GPP). Remote sensing was also used to determine the vegetation indices of normalized difference vegetation index (NDVI), photochemical reflectance index (PRI) and chlorophyll/carotenoid index (CCI) of each plot and find their relationships to the measured VPC and GPP. Nýjahraun on Heimaey and the area not affected by seabirds on Surtsey were not significantly different in any measured variable. During their initial 48-58 years of primary succession, they had reached ca. 3% (VPC) to 12-13% (GPP, VWC) of the measured variables in the 5900-year-old Lyngfellisdalur on Heimaey, which has negligible seabird nutrient inputs. However, the measured VPC and GPP had reached similar levels in only 58 years in the seabird-affected parts of Surtsey as measured on the 5900-year-old seabird-affected Elliðaey. This shows how seabirds can greatly speed up ecosystem development by oceanic nutrient inputs into terrestrial ecosystems. Significant relationships were found between NDVI and VPC and between CCI and GPP, which may become important tools to track ecosystem development in space and time on the islands.

Conifer establishment after the eruption of the Paricutin volcano in central Mexico

Volcanic eruptions have large effects on forest ecosystems and create new substrates, triggering primary succession processes. The Paricutín volcano, born in central-western Mexico, erupted between 1943 and 1952. After the cessation of the eruptive activity, plant colonization began on the lava flows and tephra deposits, including the conifer species that dominate the surrounding mature forests. This study aims to reconstruct the history of the establishment of conifer trees on the substrates created by the Paricutín eruption. 16 sampling plots were established along three transects with northern, southern, and south-western aspects, located every 250 ​m from the preserved forest to the volcanic cone. Increment cores from 400 conifer trees were extracted and their age was determined by cross-dating annual tree rings. The order of the species colonization and the tree establishment, abundance, and dominance patterns were characterized. Also, the influence of the distance from the mature forests and the inter-annual climatic conditions on the temporal tree establishment pattern was evaluated. Eight pine and one fir species have been established since 1970, only 18 years after the end of the eruptive period. However, tree establishment increased by 12.9% annually after 1995, with the youngest tree in our sample getting established in 2015. We did not find a well-defined temporal and spatial pattern of species arrival, which suggests that colonization occurred randomly, although the four pine species that were established early became the most abundant and dominant. Tree establishment was not influenced by the distance from the mature forest, and wet inter-annual conditions did not enhance pulses of tree recruitment, exhibiting a continuous tree establishment pattern. Conifer species have shown a great capacity for colonizing volcanic substrates created by the Paricutín eruption, which suggests that tropical montane conifers can regenerate rapidly under high-magnitude disturbances. These findings support the use of these forest species for ecological restoration.

A new multifractal-based grain size distribution model

Previous works related to the application of the multifractal theory for analyzing the grain size distribution (GSD), showed the potential of this approach to deal with this complex issue. However, absence of the practical application of this kind of statistical analysis raised some doubts among the soil scientists. Compared to the experimental dry sieving method, which is based on mass representations of different grain sizes, the approach presented in this work relies on the analysis of grain densities (density indicators) scanned by means of X-ray CT (Computed Tomography). By reducing the resolution of the scanned soil image(s), the cumulative representation of solid particles equal to or larger than the actual discretization element can be determined, and described analytically by means of the universal multifractals (UM).For validation of the new UM approach, the X-ray CT results of three different soils were used: the volcanic substrate covering Green Wave (a green roof of Champs-sur-Marne in France), and two horizons of the soil collected from the low land mountain area of Sierra de Guadarrama in Spain. Comparison between the proposed UM model and the experimental data of these three materials confirms that the GSD can be reasonably well predicted from the scanned images of soils covering wide range of grain sizes. The UM model, unlike the fractal-based models, accounts for fractal dimension that depends on grain size, and hence, based on the preliminary results presented in this work, it could be rather useful in case of multi-modal soils whose GSD curves are described with multiple fractal dimensions.

Evolution of Jurassic intertrap deposits in the Parnaíba Basin, northern Brazil: The last sediment-lava interaction linked to the CAMP in West Gondwana

The opening of the Central Atlantic Ocean was accompanied by ascending plume zones that generated large igneous provinces (LIPs), such as the Central Atlantic Magmatic Province (CAMP), with voluminous lava flows and outpourings. One of the best records of the CAMP in the West Gondwana is the Jurassic volcanic-sedimentary succession exposed in the western Parnaíba Basin, northern Brazil. Diagenetic and hydrothermal processes are discussed, focusing on the lava-sediment interaction. The siliciclastic sediments called “intertrap deposits” record a wet desert system characterized by fluvial-aeolian and shallow lake deposits engulfed by lavas of the CAMP at approximately 200–202 Ma. The facies and petrographic studies, based on a drill core and outcrops, led to the interpretation of the palaeoenvironmental and diagenetic evolution of the intertrap deposits. The intertrap deposits are sandwiched by basalts and may be organized in seven sedimentary facies, grouped into two facies associations: 1) ephemeral braided river deposits (FA1), which consist of medium- to coarse-grained pebbly sandstone with poorly sorted angular to sub-rounded grains (basaltic fragments and quartz) and low-angle cross-bedding, even-parallel stratification, and trough cross-stratification, and 2) pond/shallow lake deposits (FA2) composed of tabular beds of sandstone/siltstone rhythmite and laminated mudstone. The main architectural elements of intertrap deposits are 1) channels on volcanic substrate, 2) sand sheets deposited over pre-existent lava topography, 3) tabular beds with laminated rhythmites, and 4) sand-filled fissures/fractures and clastic dykes. The intensification of magmatic processes due to the disruption of Pangaea promoted the formation of extensive volcanic plains, whereas wet desert settings were developed during the quiescent intervals between lava flow episodes. Fluvial channels with subaqueous dunes and sand sheets were incised into the basaltic substrate. The abandoned fluvial plains were affected by flash floods that promoted mechanical infiltration of clays, forming coatings over grains. The heat flow and hydrothermal activity of volcanic rocks increased the devitrification of glassy clasts, releasing silica and precipitating low-temperature authigenic mineral assemblages. The most common pore-filling process was the massive precipitation of early diagenetic-hydrothermal minerals, including smectite, chalcedony, poikilotopic zeolite, megaquartz, and haematite, which partially obliterated the primary porosity and permeability. These exceptional conditions of cementation triggered by basalt eruptions precluded the modification of a primary framework by late stages (post-Jurassic) burial diagenesis. The intertrap sandstones represent the last lava-sediment interaction related to the CAMP recorded in West Gondwana.

Ecophysiological Performance of Proteaceae Species From Southern South America Growing on Substrates Derived From Young Volcanic Materials.

Southern South American Proteaceae thrive on young volcanic substrates, which are extremely low in plant-available phosphorus (P). Most Proteaceae exhibit a nutrient-acquisition strategy based on the release of carboxylates from specialized roots, named cluster roots (CR). Some Proteaceae colonize young volcanic substrates which has been related to CR functioning. However, physiological functioning of other Proteaceae on recent volcanic substrates is unknown. We conducted an experiment with seedlings of five Proteaceae (Gevuina avellana, Embothrium coccineum, Lomatia hirsuta, L. ferruginea, and L. dentata) grown in three volcanic materials. Two of them are substrates with very low nutrient concentrations, collected from the most recent deposits of the volcanoes Choshuenco and Calbuco (Chile). The other volcanic material corresponds to a developed soil that exhibits a high nutrient availability. We assessed morphological responses (i.e., height, biomass, and CR formation), seed and leaf macronutrient and micronutrient concentrations and carboxylates exuded by roots. The results show that G. avellana was less affected by nutrient availability of the volcanic substrate, probably because it had a greater nutrient content in its seeds and produced large CR exuding carboxylates that supported their initial growth. Embothrium coccineum exhibited greater total plant height and leaf P concentration than Lomatia species. In general, in all species leaf macronutrient concentrations were reduced on nutrient-poor volcanic substrates, while leaf micronutrient concentrations were highly variable depending on species and volcanic material. We conclude that Proteaceae from temperate rainforests differ in their capacity to grow and acquire nutrients from young and nutrient-poor volcanic substrates. The greater seed nutrient content, low nutrient requirements (only for G. avellana) and ability to mobilize nutrients help explain why G. avellana and E. coccineum are better colonizers of recent volcanic substrates than Lomatia species.

Cluster roots of Embothrium coccineum modify their metabolism and show differential gene expression in response to phosphorus supply

Embothrium coccineum produces cluster roots (CR) to acquire sparingly soluble phosphorus (P) from the soil through the exudation of organic compounds. However, the physiological mechanisms involved in carbon drainage through its roots, as well as the gene expression involved in the biosynthesis of carboxylates and P uptake, have not been explored. In this work, we evaluated the relationship between carboxylate exudation rate and phosphoenolpyruvate carboxylase (PEPC) activity in roots of E. coccineum seedlings grown in a nutrient-poor volcanic substrate. Second, we evaluated CR formation and the expression of genes involved in the production of carboxylates (PEPC) and P uptake (PHT1) in E. coccineum seedlings grown under three different P supplies in hydroponic conditions. Our results showed that the carboxylate exudation rate was higher in CR than in non-CR, which was consistent with the higher PEPC activity in CR. We found higher CR formation in seedlings grown at 5 μM of P supply, concomitant with a higher expression of EcPEPC and EcPHT1 in CR than in non-CR. Overall, mature CR of E. coccineum seedlings growing on volcanic substrates poor in nutrients modify their metabolism compared to non-CR, enhancing carboxylate biosynthesis and subsequent carboxylate exudation. Additionally, transcriptional responses of EcPEPC and EcPHT1 were induced simultaneously when E. coccineum seedlings were grown in P-limited conditions that favored CR formation. Our results showed, for the first time, changes at the molecular level in CR of a species of the Proteaceae family, demonstrating that these root structures are highly specialized in P mobilization and uptake.

Hydrological Behaviour of Extensive Green Roofs with Native Plants in the Humid Subtropical Climate Context

Different mitigation measures with vegetation have been proposed to sustainably manage rainwater, among which green roofs have demonstrated to be a valid solution in urbanized areas. Green roofs have gained interest also in Italy, but their spreading is generally based on application of ready-to-use packages, poorly tested in the specific climate conditions. A study was carried out to evaluate the green roof solution most suitable in the humid, subtropical climate context of Veneto Plain (north-eastern Italy) to reduce outflow volumes from building roofs into the urban drainage systems. Twelve different microcosm combinations of extensive green roof (three plant mixtures × two substrates × two storage/drainage layers) were tested and compared with gravel (considered as a conventional flat roof with gravel ballast). The tested drainage/storage layers were a preformed layer in recycled HDPE (PL) and an expanded perlite mineral layer (ML), and the growth medium layers were recycled brick substrate (RS) and volcanic substrate (VS). Three different mixtures of native plant species were transplanted: Sedum (SE), herbaceous perennial (HE), and suffruticose (SF). Results showed that all the green roof systems have a good ability to manage rainwater, with a retention ranging on average from 46.2% (SE-RS-PL microcosms) to 62.9% (SF-RS-ML microcosms) of the precipitation in the two-year period (September 2014–August 2016), against 15.4%, retained by gravel. Over the two-year period, the retained rainfall volumes were about 100% for all the light rainy events (<10 mm) and varied within a range of 48–95% for medium rainy events (≥10 and <25 mm) and 20–88% for heavy rainy events (≥25 mm), depending on rainfall depth and the antecedent weather period. The layer that gave the highest relative contribution to the stormwater retention was the vegetation layer, followed by the drainage/storage layers and then the substrate layer. In particular, SF plants decreased the outflows by 15.2% on average compared to SE, and ML layer retained more than 10% of precipitation compared to PL layer. At last, the analysis of variance showed that, within each layer, the more effective in water retention, able to generate less outflow volumes, was similarly suffruticose and herbaceous mixtures, the crushed bricks substrate, and the mineral drainage/storage layer.

Performance of Three Different Native Plant Mixtures for Extensive Green Roofs in a Humid Subtropical Climate Context

Most of the services and benefits of green roofs are related to the substrate as well as the vegetation layer. Although plant selection should be made on the basis of green roof typology, morphology, and climate conditions, very often, Sedum species only are used worldwide. However, they do not always guarantee the best performances; hence, it is important to investigate different plant species and their performance in different climate contexts. Herein, an experiment was conducted using three plant mixes (i.e., a Sedum mix, a perennial herbaceous mix, and a suffruticose mix), grown in boxes containing two substrates (a volcanic substrate or a recycled crushed brick substrate) and two drainage/storage layers (a preformed layer or a mineral layer), in factorial combination. The Sedum mix showed a high canopy cover, comparable to or even higher than that of the other mixes, particularly when supplemental irrigation was stopped. However, the actual crop coefficient (Kcact) of the herbaceous and suffruticose mixes was often higher than that of the Sedum mix. The results also showed that both the substrate and the drainage/storage layer may improve Kcact values as a consequence of their capacity for stormwater retention.

High geogenic arsenic concentrations in travertines and their spring waters: Assessment of the leachability and estimation of ecological and health risks

Travertines and their springs are rarely investigated as a source of toxicity. Remarkably high contents of As (up to 10 g/kg) have been found in travertine deposits and associated spring waters, nearby Ghorveh city (western Iran). Two types of travertines were distinguished: (i) Fissure ridge travertines, in areas with a carbonate-dominated basement, are characterized by a relatively low content and leaching of As. Their spring waters contain > 150 µg/L of As; (ii) Mound travertines, rich in non-carbonate impurities, occur in areas with volcanic substrates and contain high As concentrations (on average ~1,500 mg/kg) with high leachability. Their spring waters have lower As concentrations than equivalent fissure ridge waters. Principal Component Analyses of the elemental and mineralogical composition show the unstable association of As over a wide range of pH values to non-carbonate related elements, in particular iron, related to clay minerals. The high potential release of As may result in adverse ecotoxicological effects in surrounding agricultural soils and crops. An ecological risk assessment confirms the enrichment and very high potential ecological risk of As around mound carbonates. The human health risk assessment based on calculation via exposure factors suggests adverse non-carcinogenic and high carcinogenic risk with regard to As, both for adults and children.

Gevuina avellana and Lomatia dentata, two Proteaceae species from evergreen temperate forests of South America exhibit contrasting physiological responses under nutrient deprivation

Gevuina avellana and Lomatia dentata are Proteaceae species from evergreen temperate forests, but only G. avellana can colonize nutrient deprived volcanic depositions. We hypothesized that under nutrient deprivation, G. avellana would present higher survival, physiological performance, and adjustment regarding cluster root (CR) formation and carboxylate exudation rate than L. dentata. We evaluated relative growth rate, maximal photosynthetic rate, photochemical performance, nitrogen (N) and phosphorus (P) leaf concentrations, specific leaf area, photosynthetic P and N use efficiency (PPUE and PNUE), CR formation and carboxylate exudation rate. Plants were grown in a greenhouse, using recent volcanic substrate and watered with different nutrient Hoagland (H) solutions: modified full Hoagland, without P, without N, or tap water. Both species showed high survival. G. avellana exhibited higher growth rates (RGR), and higher CR number and biomass allocation under nutrient deprivation, but lower carboxylate exudation rates than L. dentata. Malate, oxalate and succinate were detected in root exudates of G. avellana but only oxalate in L. dentata. However, PPUE and PNUE were higher in L. dentata than in G. avellana . Our hypothesis was not entirely accepted, CR formation was more “constitutive” in G. avellana, and composition of carboxylates was more diverse, with lower exudation rates than L. dentata. Moreover, L. dentata showed higher PNUE and PPUE, partly explained by thinner leaves. Different responses are related with edaphic conditions, where both species inhabit: more diverse to G. avellana and restricted to developed soils to L. dentata.

A Device for the Simultaneous Determination of the Water Retention Properties and the Hydraulic Conductivity Function of an Unsaturated Coarse Material; Application to a Green-Roof Volcanic Substrate

Abstract The determination of the water retention curve (WRC) and hydraulic conductivity function (HCF) of a specific volcanic coarse granular material used as a substrate for urban green roofs in Europe was carried out on a newly developed specific device in which low suctions, typical of coarse granular materials, were controlled. Smaller suctions (up to 32 kPa) were imposed by using a hanging column system, and larger suctions (between 32 and 50 kPa) were imposed by using the axis translation technique in the same cell. The changes in suction during the tests were monitored by using a high accuracy differential pressure transducer. They were also used to determine the HCF by means of both Kunze and Kirkham’s and Gardner’s methods. The former technique was used at low suctions (<4 kPa) to account for the impedance effects due to the high air entry value ceramic porous disk and the latter was used between 4 and 50 kPa. Good comparability was observed in the data from both methods, demonstrating the good performance of the device. The mathematical expressions of the WRC of van Genuchten and Brooks and Corey were used, and a good fitting with our experimental data was obtained. Conversely, the HCFs derived from these expressions appeared to lead to a significant underestimation, confirming the need of an operational and simple device for the experimental determination of the HCF. Also, this material proved to be an appropriate material for green urban infrastructures, because of its lightweight, satisfactory water retention capability and hydraulic conductivity.