Assessment of sources and health risks of heavy metals in metropolitan household dust among preschool children: The LEAPP-HIT study.

The most common construction material used in Taiwan is concrete, potentially contaminated by geologic heavy metals (HMs). Younger children spend much time indoors, increasing HM exposure risks from household dust owing to their behaviors. We evaluated arsenic (As), cadmium (Cd), and lead (Pb) concentrations in fingernails among 280 preschoolers between 2017 and 2023. We also analyzed HM concentrations, including As, Cd, Pb, chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), iron (Fe), and manganese (Mn), in 90 household dust and 50 road dust samples from a residential area where children lived between 2019 and 2021 to deepen the understanding of sources and health risks of exposure to HMs from household dust. The average As, Cd, and Pb concentrations in fingernails were 0.12 ± 0.06, 0.05 ± 0.05, and 0.95 ± 0.77 µg/g, respectively. Soil parent materials, indoor construction activities, vehicle emissions, and mixed indoor combustion were the pollution sources of HMs in household dust. Higher Cr and Pb levels in household dust may pose non-carcinogenic risks to preschoolers. Addressing indoor construction and soil parent materials sources is vital for children's health. The finding of the present survey can be used for indoor environmental management to reduce the risks of HM exposure and avoid potential adverse health effects for younger children.

Rare earth elements in tea garden soils and their bioavailability to tea buds in Taiwan.

Tea (Camellia sinensis) is a widespread beverage plant that prefers aluminum-enriched acidic soils. However, rare earth elements (REEs) might be highly phyto-available in these soils. With the increasing demands for REEs in high-technology industries, understanding the dynamics of REEs in the environment is essential. Thus, this study identified the total concentration of REEs in the root-zone soils and corresponding tea buds (n = 35) collected from tea gardens in Taiwan. Additionally, the labile REEs in the soils were extracted with 1 M KCl, 0.1 M HCl, and 0.05 M ethylenediaminetetraacetic acid (EDTA) to elucidate the fractionation tendency of REEs in the soil-plant system and the relationships between REEs and Al in the tea buds. The concentration of light REEs (LREEs) was higher than those of medium REEs (MREEs) and heavy REEs (HREEs) in all soil and tea bud samples. According to the upper continental crust (UCC) normalization, MREEs and HREEs were more abundant than LREEs in the tea buds. Furthermore, REEs remarkably increased with increasing Al in the tea buds, whereas the linear correlations between Al and MREEs and HREEs were stronger than between LREEs. Compared with LREEs, the extractabilities of MREEs and HREEs by all single extractants in the soils were higher, coinciding with their higher UCC-normalization-based enrichments in the tea buds. Moreover, the 0.1 M HCl- and 0.05 M EDTA-extractable REEs were affected by soil properties and significantly correlated with the total REEs in the tea buds. The concentration of REEs in the tea buds was successfully predicted by empirical equations of extractable REEs with 0.1 M HCl and 0.05 M EDTA, as well as general soil properties including pH, organic carbon, dithionite-citrate-bicarbonate-extractable iron, aluminum, and phosphorus. However, this prediction should be further verified using many soil and tea types in the future.

Oral and inhalation bioaccessibility of mercury in contaminated soils and potential health risk to the kidneys and neurodevelopment of children in Taiwan.

Health risk assessments of exposure to mercury (Hg) from soils via ingestion and inhalation are indispensable for Taiwanese people living in the vicinity of Hg-contaminated sites. In this study, anthropogenic soils were collected from various polluted sources in Taiwan. In vitro oral and inhalation bioaccessible fractions of Hg were analyzed to avoid from overestimating the exposure risk. Discrepancies in oral and inhalation bioaccessible levels of Hg in soils were found using different in vitro assays with different pH levels and chemical compositions. The freshly contaminated soil (soil S7) polluted by chlor-alkali production activity sampled before the site was remediated had the highest total Hg concentration of 1346 mg/kg, with the highest oral bioaccessibility of 26.2% as analyzed by SW-846 Method 1340 and inhalation bioaccessibility of 30.5% as analyzed by modified Gamble's solution. The lesser extent of aging of Hg in soil S7 increased the Hg availability for humans, which was also found based on results of a sequential extraction procedure. Results of the hazard quotient showed that soil ingestion was the main pathway causing non-carcinogenic risks for children and adults. Children were also exposed to higher risks than were adults due to higher frequencies of hand-to-mouth behaviors and lower body weights. Furthermore, hazard index results adjusted for oral and inhalation bioaccessible Hg were lower than those obtained based on the total Hg content; however, an unacceptable value of the non-carcinogenic risk (> 1) for children living near soil S7 was still observed. This study suggests that children living near sites polluted for a short period of time may suffer potential renal effects regardless of the bioaccessibility. Our findings provide suggestions for decision makers on setting new strategies for managing risks of Hg-contaminated soils in Taiwan.

A photosynthetic bacterial inoculant exerts beneficial effects on the yield and quality of tomato and affects bacterial community structure in an organic field.

Plant growth-promoting rhizobacteria (PGPR) are microorganisms that promote plant health and play a critical role in sustainable agriculture. As a PGPR, Rhodopseudomonas palustris strain PS3, when applied as a microbial inoculant, exhibited beneficial effects on a variety of crops. In this study, we investigated the effects of PS3 on tomato growth, soil properties, and soil microbiota composition in an organic field. The results demonstrated that PS3 inoculation significantly improved the yield of marketable tomato fruit (37%) and the postharvest quality (e.g., sweetness, taste, vitamin C, total phenolic compounds, and lycopene). Additionally, soil nutrient availability (35-56%) and enzymatic activities (13-62%) also increased. We detected that approximately 107 CFU/g soil of R. palustris survived in the PS3-treated soil after harvest. Furthermore, several bacterial genera known to be associated with nutrient cycling (e.g., Dyella, Novosphingobium, Luteimonas, Haliangium, and Thermomonas) had higher relative abundances (log2 fold change >2.0). To validate the results of the field experiment, we further conducted pot experiments with field-collected soil using two different tomato cultivars and obtained consistent results. Notably, the relative abundance of putative PGPRs in the genus Haliangium increased with PS3 inoculation in both cultivars (1.5 and 34.2%, respectively), suggesting that this genus may have synergistic interactions with PS3. Taken together, we further demonstrated the value of PS3 in sustainable agriculture and provided novel knowledge regarding the effects of this PGPR on soil microbiota composition.

Release and mobilization of Ni, Co, and Cr under dynamic redox changes in a geogenic contaminated soil: Assessing the potential risk in serpentine paddy environments.

The release dynamics and mobilization of geogenic Ni, Co, and Cr in serpentine paddy soils under fluctuating redox conditions have not yet been well studied. Here we investigated the release dynamics of Cr, Co, and Ni and controlling factors (e.g., Fe, Mn, Mg, Cl-, PO43-, SO42-, and dissolved organic carbon (DOC)) in a geogenic-contaminated serpentine soil under wide range of redox potential (EH) changes. The effects of re-oxidation process have been also investigated. The soil was incubated for 28 days and EH was controlled from oxidation (+200 mV) to reduction (-200 mV) and re-oxidation (+240 mV) using a microcosm setup in duplicates. The slurry pH increased, along with decreasing EH. The average concentration of dissolved Co (17.1-23.6 µg L-1) decreased under low EH/high pH and vice versa. The average concentration of dissolved Cr decreased sharply from 624 µg L-1 to 54.4 µg L-1 with decreasing EH from +200 mV to 0 mV and the associated increase of pH from 7.8 to 8.5; then, it was constant around 24.5 µg L-1. Concentration of dissolved Ni was lower (73.5-84.6 µg L-1) under high EH at the first week of incubation; then, increased to 108.5 µg L-1 under low EH (-200 mV); thereafter, increased more at the end up to 124.5 µg L-1 at high EH (+240 mV), because of the pH decrease. A factor analysis identified that Cr and Co formed one group with Mn and Mg, while Ni was clustered together with Cl-, DOC, and SO42-. This indicates that the redox-induced release dynamic of Cr and Co was mainly governed by MnMg compounds, while the release of Ni was mainly affected by the aliphatic compounds of DOC and the redox chemistry of chlorides and sulfur in this soil. The re-oxidation increased the mobilization of Ni and Co and did not affect the release of Cr. These findings suggest that the redox-induced mobilization of geogenic Co, Ni, and Cr from soil to water in serpentine rice soils should be considered due to the high solubility and thus the associated bioavailability and potential environmental and human health risks, when such metal-enriched soils will be used for agricultural flood-dry cycle systems.

Air pollutant removal by four sidewalk tree species in the largest city in Taiwan.

Air pollutants pose risks to human health, especially in densely populated cities. We compared the interception of suspended particles and metal elements by four sidewalk tree species with different leaf surface wettability (based on contact angle), leaf area, and phenology in Taipei, Taiwan. Suspended particles were enriched 2.0-2.5 times in throughfall relative to rainfall due to wash-off of suspended particles deposited on leaf surfaces during rainless periods. The enrichment in throughfall was greater in tree species with larger leaf areas. Despite greater concentrations of suspended particles in rainfall during the low-leaf-area period, enrichment was greater in the high-leaf-area period, indicating that leaf area was a key factor affecting canopy interception of pollutants. Throughfall enrichment of suspended particles positively correlated with water quantity, indicating that air pollutants intercepted by tree canopies were not fully washed off by rainfall. Annually, ∼830 g of suspended particles were intercepted and washed off from one tree canopy, with a crown area of 42 m2 . Scaling up, a rough estimate of 72.7 Mg of suspended particles were intercepted annually by the 90,000 sidewalk trees in Taipei City. Copper, chromium, and aluminum were enriched in throughfall compared with rainfall. However, lead was depleted in throughfall, indicating greater interception than wash-off. Based on our results, leaf area and length of foliated period are key characteristics affecting canopy interception of particulate matter and associated metal elements, whereas leaf surface wettability is of secondary importance.

Comparison of bacterial communities and their functional profiling using 16S rRNA gene sequencing between the inherent serpentine-associated sites, hyper-accumulator, downgradient agricultural farmlands, and distal non-serpentine soils.

This study aims to determine and compare the bacterial community and functional profiles associated with serpentine sites, innate hyper-accumulating weed, downgradient agricultural farmlands and non-serpentine sites using 16S rRNA gene sequencing. Elemental analysis revealed that the serpentine rock and weathered soil have higher magnesium, nickel, chromium, magnesium/calcium and lower calcium/magnesium ratios and agricultural farmlands have recorded elevated chromium. Proteobacteria were found predominant, except the non-serpentine site which was rich in Cyanobacteria. PCA analysis at the genus level indicates the uniqueness of different experimental groups, except the hyperaccumulators which exhibited relatively less dissimilarity. The shift analysis showed the serpentine sites were characterized by the abundance of bacteria having heavy metal effluxion. The hyper-accumulating weeds were higher in plant growth-promoting bacteria expressing tolerance against heavy metals toxicity such as nickel, chromium, cobalt and arsenic. Besides, the agricultural lands were abundant in wetland-associated methanogens and metal (manganese, iron and zinc) transporting function related bacteria. The results suggest that the inherent edaphic factors including heavy metal content, the interacting behavior of hyperaccumulator's rhizosphere microbiota with soil and anthropogenic activities such as agricultural practices could be a major determinant of the variation in the bacterial community selection and abundance in the respective study sites.

Pedogeochemical distribution of gallium, indium and thallium, their potential availability and associated risk in highly-weathered soil profiles of Taiwan.

Gallium (Ga), indium (In), and thallium (Tl) are emerging soil contaminants. Profile distribution of total content and available form as well as assessing the contamination degree of these elements in highly-weathered soils have not been studied. Consequently, the aim of this study was to determine the distribution of total (HF-digestion) and available (EDTA-extracted form) content of Ga, In, and Tl in eleven soil profiles collected from aged fluvial materials on the Quaternary terraces representing highly-weathered soils (Ultisols and Oxisols) in Taiwan as affected by soil properties. We also assessed the soils contamination degree using indices including enrichment factor (EF), geo-accumulation index (Igeo), and pollution loading index (PLI). The total element content varied from 9460 to 2340 µg kg-1 for Ga, 4.77-37.1 µg kg-1 for In, and from 55.7 to 206 µg kg-1 for Tl. The elements showed different profile distribution in the soils. Soil contamination degree was low in all profiles according to the Igeo and PLI values, but the contamination degree according to the EF was severe for Ga and minor or moderate for In in selected horizons of some profiles. The median content of EDTA-extracted Ga, In, and Tl accounted for 24.0, 8.70, and 5.1% of the total content, respectively. The available Ga and Tl can be predicted by a function of total element and clay using multivariate linear regression analysis. The available In was not able to be predicted by a significant fit of the regression with total In and the studied soil properties, and thus we require more assessment approaches of In availability for the soils in the future.

Bioaccumulation and human health risk assessment of chromium and nickel in paddy rice grown in serpentine soils.

The natural abundance of Cr and Ni in serpentine soils is well-known, but the food safety of rice grown in these hazardous paddy soils is poorly understood. The study evaluated the bioaccumulation of chromium (Cr) and nickel (Ni) in rice (Oryza sativa) grown in serpentine-derived paddy soils in the Philippines. Surface soil (0-20 cm) samples were collected and characterized across three (i.e., Masinloc, Candelaria, and Sta. Cruz) paddy areas in Luzon Island, Philippines. At least 3 to 4 whole rice plants at mature stage were uprooted manually in each sampling point where the soil samples were collected. The total Cr and Ni concentrations in rice (i.e., roots, shoots, and grains) and soil, soil physicochemical properties, bioaccumulation factor (BAF), translocation factor (TF), and the hazard quotients (HQ) were determined. Results revealed that Cr and Ni in rice were accumulated mostly in the roots. Although paddy soils had elevated total Cr and Ni concentrations, the BAF and soil-to-root TF values for Cr and Ni were < 1. In terms of human health risks, results further revealed low risk for both male and female Filipino adults as HQ values for Cr and Ni were < 1. While it is safe to consume rice grown in the area in terms of Cr and Ni dietary intake, more studies are necessary to understand the dynamics and bioavailability of these heavy metals in other crops and drinking water from tube wells in these areas in order to provide a more holistic human health-based assessments and to ensure consumer safety in serpentine areas. In addition, a more reliable data on Cr and Ni speciation in serpentine soils and crops is critically important. Further studies are also needed to understand the contribution of bioavailable heavy metals in improving the soil health to achieve food safety.

The influence of soil age on ecosystem structure and function across biomes.

The importance of soil age as an ecosystem driver across biomes remains largely unresolved. By combining a cross-biome global field survey, including data for 32 soil, plant, and microbial properties in 16 soil chronosequences, with a global meta-analysis, we show that soil age is a significant ecosystem driver, but only accounts for a relatively small proportion of the cross-biome variation in multiple ecosystem properties. Parent material, climate, vegetation and topography predict, collectively, 24 times more variation in ecosystem properties than soil age alone. Soil age is an important local-scale ecosystem driver; however, environmental context, rather than soil age, determines the rates and trajectories of ecosystem development in structure and function across biomes. Our work provides insights into the natural history of terrestrial ecosystems. We propose that, regardless of soil age, changes in the environmental context, such as those associated with global climatic and land-use changes, will have important long-term impacts on the structure and function of terrestrial ecosystems across biomes.

Soil contamination by potentially toxic elements and the associated human health risk in geo- and anthropogenic contaminated soils: A case study from the temperate region (Germany) and the arid region (Egypt).

The aim of this study was to assess the soil contamination caused by potentially toxic elements (Al, As, Co, Cr, Cu, Fe, Mn, Mo, Ni, Se, V, and Zn) using various indices and the associated risk of human health for adults and children in selected soils from Germany (Calcic Luvisols, Tidalic Fluvisols, Haplic Gleysols, and Eutric Fluvisols) and Egypt (Haplic Calcisols, Sodic Fluvisols, and Eutric Fluvisols). Soil contamination degree has been assessed using indices such as contamination factor (CF), pollution load index (PLI), geo-accumulation index (Igeo), and enrichment factor. We also assessed the health risk for children and for male and female adults. Chromium, Cu, As, Mo, Ni, Se, and Zn in the German Fluvisols had high CF of >6, while in the Egyptian Fluvisols Se, Mo, As, and Al revealed a high CF. The PLI (1.1-5.2) was higher than unity in most soils (except for Tidalic Fluvisols), while the most important contributor was Se, followed by Mo and As in the Egyptian Fluvisols, and by Cr, Cu, and Zn in the German Fluvisols. The median value of hazard index (HI) for children in the studied soils indicated an elevated health risk (higher than one), especially in the German Fluvisols (HI = 4.0-29.0) and in the Egyptian Fluvisols (HI = 2.2-5.2). For adults, median HIs in all soils were lower than unity for both males and females. The key contributor to HI was As in the whole soil profiles, accounting for about 59% of the total HIs in all three person groupings. Our findings show that in the studied multi-element contaminated soils the risk for children's health is higher than for adults; while mainly As (and Al, Cr, Cu, and Fe) contributed significantly to soil-derived health risk.

Multiple elements of soil biodiversity drive ecosystem functions across biomes.

The role of soil biodiversity in regulating multiple ecosystem functions is poorly understood, limiting our ability to predict how soil biodiversity loss might affect human wellbeing and ecosystem sustainability. Here, combining a global observational study with an experimental microcosm study, we provide evidence that soil biodiversity (bacteria, fungi, protists and invertebrates) is significantly and positively associated with multiple ecosystem functions. These functions include nutrient cycling, decomposition, plant production, and reduced potential for pathogenicity and belowground biological warfare. Our findings also reveal the context dependency of such relationships and the importance of the connectedness, biodiversity and nature of the globally distributed dominant phylotypes within the soil network in maintaining multiple functions. Moreover, our results suggest that the positive association between plant diversity and multifunctionality across biomes is indirectly driven by soil biodiversity. Together, our results provide insights into the importance of soil biodiversity for maintaining soil functionality locally and across biomes, as well as providing strong support for the inclusion of soil biodiversity in conservation and management programmes.

Influence of soil properties on the bioaccessibility of Cr and Ni in geologic serpentine and anthropogenically contaminated non-serpentine soils in Taiwan.

Serpentine minerals with high levels of geologic chromium (Cr) and nickel (Ni) and non-serpentine farmlands polluted by irrigation water causing high anthropogenic Cr and Ni levels are both found in Taiwan. Elevated levels of Cr and Ni in these soils are a concern due to their potential to promote cancer mortality in humans. Bioaccessibility is a crucial factor determining the actual health risk via oral ingestion when children are exposed to metal-contaminated soils. Furthermore, the bioaccessibility of metals varies with the source, soil properties, and fractionation of metals in the soil. Therefore in this study, soil pH, total organic carbon (TOC), texture, and the total concentrations, fractionation, and bioaccessibility of Cr and Ni were analyzed and correlated for soils collected from serpentine mineral-containing deposits and contaminated non-serpentine farmlands. The low bioaccessibility and low mobility of Cr and Ni in serpentine soils suggested that incidental ingesting of soils posed a low health risk; however, the higher bioaccessibility and mobility of Ni in non-serpentine soils contaminated by electroplating wastewater could lead to potential risks for humans. Additionally, a significant difference in the bioaccessibility of Ni was observed between serpentine and non-serpentine soils, but this was not shown for Cr. Accordingly, a correlation analysis showed that Cr bioaccessibility was positively correlated with TOC, with no distinction between serpentine and non-serpentine soils. In contrast, TOC and the fractions of the sequential extraction procedure were significantly correlated with Ni bioaccessibility both in anthropogenically contaminated non-serpentine soils and in natural serpentine soils.

Evaluating vanadium bioavailability to cabbage in rural soils using geochemical and micro-spectroscopic techniques.

Assessing the vanadium (V) fractionation and speciation to predict its bioavailability using a combined approach of geochemical extractions and micro-spectroscopic techniques is still not well studied. Therefore, we aimed to determine the bioavailability of V in rural soils using single extractants, sequential extraction procedure, and the X-ray absorption near edge structure (XANES) spectroscopy. We collected and characterized ninety four samples originated from horizons of seventeen soil profiles in Taiwan. We determined the total content of V and its geochemical fractions using the BCR sequential extraction procedure to predict its potential mobility. We also assessed the bioavailability of V in the soils using four availability indices i.e., CaCl2, HCl, ethylenediaminetetraacetic acid (EDTA), and NaHCO3 and related them to its uptake by Chinese cabbage (Brassica chinensis L.). Additionally, we determined the V speciation by vanadium K-edge XANES spectra. Moreover, we studied the elemental compositions of the soils using Electron Probe Micro Analysis (EPMA). Vanadium was mainly distributed in the residual fraction (81-98% of total V). Among the potential mobile fractions, V was mainly associated with Fe oxides, as identified by the BCR sequential extraction and EMPA. The XANES analysis indicated that V mainly existed in the soils as V(IV) and V(V). The EDTA and NaHCO3 extracted more V than CaCl2 and HCl, and both, particularly NaHCO3 were positively and significantly correlated with the total soil content and plant shoot concentrations of V; therefore NaHCO3 might be recommended as a bioavailability index for soil V. We hypothesize that the NaHCO3 may extract vanadate from soil surfaces and also vanadate transformed from vanadyl at alkaline pH during the extraction. The NaHCO3-extracted V can be predicted by a function of soil total V, CEC, and pH. Our results should be verified using different soils and plants in the future.

Evolution of As speciation with depth in a soil profile with a geothermal As origin.

High contents of arsenic were detected in soils in Guandu plain, northwest Taiwan. To determine the sources and speciation of As in the soils, the depth profiles of soil properties, elemental composition and As speciation were investigated. The As concentrations in the soil profile ranged from 152 to 1222 mg kg-1, with the highest concentration at the depth of 70-80 cm. The As distribution was found to be positively correlated to Fe, Pb, and Ba. The As(V)-adsorbed ferrihydrite and scorodite were the predominant phases in the top layers (<50 cm), while beudantite was the predominant phase below 50 cm along with As(III)- and As(V)-adsorbed ferrihydrite as the minor components. The results of sequential extraction showed that As-associated with noncrystalline and crystalline Fe/Al hydrous oxides and residual phases were predominant at the depths of 0-60, 60-100 and 100-140 cm, respectively, indicating an increasing As recalcitrance with soil depth. Based on the soil properties, and elemental and mineral compositions at different soil depths, the origin of beudantite in the soils was likely allogenic rather than authigenic or anthropogenic. The formation of scorodite in the surface soils was suggested to be transformed from beudantite. As-associated Fe hydrous oxides may be contributed by the progressive dissolution of beudantite and scorodite, and the continuous influxes of As and Fe. While Fe hydrous oxides were able to immobilize As during the dissolution of As-bearing minerals, the increase of As mobility in soils may imply an increase in the environmental risk of As over time.

Global ecological predictors of the soil priming effect.

Identifying the global drivers of soil priming is essential to understanding C cycling in terrestrial ecosystems. We conducted a survey of soils across 86 globally-distributed locations, spanning a wide range of climates, biotic communities, and soil conditions, and evaluated the apparent soil priming effect using 13C-glucose labeling. Here we show that the magnitude of the positive apparent priming effect (increase in CO2 release through accelerated microbial biomass turnover) was negatively associated with SOC content and microbial respiration rates. Our statistical modeling suggests that apparent priming effects tend to be negative in more mesic sites associated with higher SOC contents. In contrast, a single-input of labile C causes positive apparent priming effects in more arid locations with low SOC contents. Our results provide solid evidence that SOC content plays a critical role in regulating apparent priming effects, with important implications for the improvement of C cycling models under global change scenarios.

Occurrence and cycling of trace elements in ultramafic soils and their impacts on human health: A critical review.

The transformation of trace metals (TMs) in natural environmental systems has created significant concerns in recent decades. Ultramafic environments lead to potential risks to the agricultural products and, subsequently, to human health. This unique review presents geochemistry of ultramafic soils, TM fractionation (i.e. sequential and single extraction techniques), TM uptake and accumulation mechanisms of ultramafic flora, and ultramafic-associated health risks to human and agricultural crops. Ultramafic soils contain high levels of TMs (i.e. Cr, Ni, Mn, and Co) and have a low Ca:Mg ratio together with deficiencies in essential macronutrients required for the growth of crops. Even though a higher portion of TMs bind with the residual fraction of ultramafic soils, environmental changes (i.e. natural or anthropogenic) may increase the levels of TMs in the bioavailable or extractable fractions of ultramafic soils. Extremophile plants that have evolved to thrive in ultramafic soils present clear examples of evolutionary adaptations to TM resistance. The release of TMs into water sources and accumulation in food crops in and around ultramafic localities increases health risks for humans. Therefore, more focused investigations need to be implemented to understand the mechanisms related to the mobility and bioavailability of TMs in different ultramafic environments. Research gaps and directions for future studies are also discussed in this review. Lastly, we consider the importance of characterizing terrestrial ultramafic soil and its effect on crop plants in the context of multi-decadal plans by NASA and other space agencies to establish human colonies on Mars.

Soil and biomass carbon re-accumulation after landslide disturbances.

In high-standing islands of the Western Pacific, typhoon-triggered landslides occasionally strip parts of the landscape of its vegetative cover and soil layer and export large amounts of biomass and soil organic carbon (OC) from land to the ocean. After such disturbances, new vegetation colonizes the landslide scars and OC starts to reaccumulate. In the subtropical mountains of Taiwan and in other parts of the world, bamboo (Bambusoideae) species may invade at a certain point in the succession of recovering landslide scars. Bamboo has a high potential for carbon sequestration because of its fast growth and dense rooting system. However, it is still largely unknown how these properties translate into soil OC re-accumulation rates after landslide disturbance. In this study, a chronosequence was established on four former landslide scars in the Central Mountain Range of Taiwan, ranging in age from 6 to 41 years post disturbance as determined by landslide mapping from remote sensing. The younger landslide scars were colonized by Miscanthus floridulus, while after approx. 15 to 20 years of succession, bamboo species (Phyllostachys) were dominating. Biomass and soil OC stocks were measured on the recovering landslide scars and compared to an undisturbed Cryptomeria japonica forest stand in the area. After initially slow re-vegetation, biomass carbon accumulated in Miscanthus stands with mean annual accretion rates of 2 ± 0.5 Mg C ha-1 yr-1. Biomass carbon continued to increase after bamboo invasion and reached ~40% of that in the reference forest site after 41 years of landslide recovery. Soil OC accumulation rates were ~2.0 Mg C ha-1 yr-1, 6 to 41 years post disturbance reaching ~64% of the level in the reference forest. Our results from this in-situ study suggest that recovering landslide scars are strong carbon sinks once an initial lag period of vegetation re-establishment is overcome.

Changes in belowground biodiversity during ecosystem development.

Belowground organisms play critical roles in maintaining multiple ecosystem processes, including plant productivity, decomposition, and nutrient cycling. Despite their importance, however, we have a limited understanding of how and why belowground biodiversity (bacteria, fungi, protists, and invertebrates) may change as soils develop over centuries to millennia (pedogenesis). Moreover, it is unclear whether belowground biodiversity changes during pedogenesis are similar to the patterns observed for aboveground plant diversity. Here we evaluated the roles of resource availability, nutrient stoichiometry, and soil abiotic factors in driving belowground biodiversity across 16 soil chronosequences (from centuries to millennia) spanning a wide range of globally distributed ecosystem types. Changes in belowground biodiversity during pedogenesis followed two main patterns. In lower-productivity ecosystems (i.e., drier and colder), increases in belowground biodiversity tracked increases in plant cover. In more productive ecosystems (i.e., wetter and warmer), increased acidification during pedogenesis was associated with declines in belowground biodiversity. Changes in the diversity of bacteria, fungi, protists, and invertebrates with pedogenesis were strongly and positively correlated worldwide, highlighting that belowground biodiversity shares similar ecological drivers as soils and ecosystems develop. In general, temporal changes in aboveground plant diversity and belowground biodiversity were not correlated, challenging the common perception that belowground biodiversity should follow similar patterns to those of plant diversity during ecosystem development. Taken together, our findings provide evidence that ecological patterns in belowground biodiversity are predictable across major globally distributed ecosystem types and suggest that shifts in plant cover and soil acidification during ecosystem development are associated with changes in belowground biodiversity over centuries to millennia.

Release dynamics of As, Co, and Mo in a biochar treated soil under pre-definite redox conditions.

This study assessed the impact of pre-definite redox potential (EH) on the release dynamics and distribution of As, Co, and Mo between the dissolved and colloidal phases as well as their potential mobility and phytoavailability in the sediment phase of a mining soil treated with rice hull biochar (BC). The experiment was conducted from controlled moderately-reducing to oxidizing conditions using an automated biogeochemical microcosm system. Arsenic and Mo were more abundant in the dissolved phase due to their predominant in potential mobile fractions, while Co was more abundant in the colloidal phase due to its association with Fe-(hydr)oxides. Biochar increased the dissolved and colloidal concentrations of As, the dissolved concentration of Co, and the colloidal concentration of Mo under oxidizing condition. On the other hand, the application of BC decreased the dissolved concentration of Mo and the colloidal concentration of Co in the first redox cycle under reducing-acidic condition, due to lower pH values, and chemistry of sulfide-sulfate and Fe/Mn oxides. The phytoavailability of As and Co were higher than their potential mobility in the sediment phase, while the same trend was not discerned for Mo. The potential mobility and phytoavailability of As and Co were high under oxic-acidic conditions. The potential mobility and phytoavailability of Mo might be increased under oxic condition due to the dissolution of Fe and Mn oxides under lower pH conditions, especially in the BC treated soil. Application of such rice hull BC to soil might stimulate the release of As, Co, and Mo under flooding conditions, which might increase the environmental and health risks in such wetland ecosystems.