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Plant‐available silicon (Si) concentrations vary considerably across tropical soils, yet the ecological importance of that variation remains largely unresolved. Increased Si availability can enhance growth and modulate foliar nutrient status in many crop species suggesting similar effects might occur in natural systems. However, how growth, foliar Si and macronutrient concentrations as well as their stoichiometry respond to plant‐available Si and how these responses differ across tropical tree species is unknown. We experimentally exposed seedlings of 12 tropical tree species to a gradient of plant‐available Si concentrations, representing 85 % of the variation found across central Panama, and assessed responses in aboveground growth and foliar nutrient status. Furthermore, we assessed whether higher plant‐available Si increases P availability. Increasing plant‐available Si led to increased foliar Si concentrations (by up to 140%). It also led to higher aboveground growth (by up to 220%), and it affected foliar C and N concentrations, and nutrient stoichiometry across species. However, at the species‐level only a small subset of two to four species showed significant growth and foliar nutrient responses. At the soil‐level, plant‐available P remained unchanged along the experimental soil Si gradient. Our results showed that Si can improve growth and/or modulate foliar nutrient status in a number of tropical tree species. Furthermore, species' growth and foliar nutrient concentrations might vary differently across tropical forest sites varying in plant‐available Si. Additionally, Si‐induced responses in foliar nutrient stoichiometry have the potential to affect herbivory and litter decomposition. Taken together, natural variation in plant‐available Si might influence plant performance unequally across tropical tree species, and change trophic interactions, with potential implications for ecosystem processes. [ABSTRACT FROM AUTHOR]

Temperate grasslands exhibit strong spatial and temporal variation in water regimes. Thus, grassland plants experience potentially stressful water regimes, which may influence their tissue silicon (Si) and nitrogen (N) concentrations. Plant Si and N concentrations play important ecological roles in temperate grasslands, for example, by influencing plant performance and herbivory, yet comparisons of species' responses to a broad range of water regimes, including drought, waterlogging and flooding, are lacking.We conducted a mesocosm experiment with 10 temperate grassland species of two life‐forms (grasses and forbs) exposed to four different soil water regimes (drought, a benign control, waterlogged and flooded conditions), and analysed their Si and N concentrations.Grasses showed lower Si concentrations under drought and flooding compared to the benign control and the highest concentrations emerged under waterlogging. Overall, plant Si responses of grasses were more uniform, while in forbs, responses varied both in direction and magnitude across species. For N concentrations, all species and life‐forms showed the highest concentrations under drought compared to the benign control, while half of the species exhibited decreasing concentrations under waterlogging and/or flooding. The water regimes, especially waterlogging and flooding, induced changes in species rankings of plant Si and N concentrations, with stronger shifts in forbs than in grasses.Our results indicate that spatial and temporal variation of water regimes may influence plant Si and N concentrations in temperate grassland species. Plant Si responses to water regimes might be highly species‐specific in forbs but more similar in grasses, whereas plant N responses are likely to be relatively uniform across species and life‐forms.The strong plasticity in plant Si and N concentrations we observed might have pervasive consequences for ecological processes, such as herbivory. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Rice cultivation requires high amounts of phosphorus (P). However, significant amounts of P fertilizer additions may be retained by iron (Fe) oxides and are thus unavailable for plants. At the same time, rice cultivation has a high demand for silicic acid (Si), reducing Si availability after short duration of rice cultivation. By studying a paddy chronosequence with rice cultivation up to 2000 years, we show that Si limitation, observed as early as a few decades of rice cultivation, is limiting P availability along the paddy soils chronosequence. Using near edge X-ray absorption fine structure spectroscopy (NEXAFS) in a scanning transmission (soft) X-ray microscope (STXM) we show release of available P was linked to a Si-induced change in speciation of Fe-phases in soil particles and competition of Si with P for binding sites. Hence, low Si availability is limiting P availability in paddy soils. We propose that proper management of Si availability is a promising tool to improve the P supply of paddy plants. [ABSTRACT FROM AUTHOR]

Purpose: Silicon (Si) accumulation is an important strategy for plant defense against biotic and abiotic stress. Solid amorphous silica (ASi) deposits have been found to protect plants against different stressors (e.g., drought stress, ultraviolet radiation, herbivory, and pests). Most research on ASi deposits and their subsequent function is conducted under lab conditions. However, it is still unclear at which stage in ontogeny ASi deposits are developed to fulfill their function in plant protection under field conditions. Methods: We combined SEM–EDX, NMR spectroscopy, and Si extractions to analyze silicification patterns in wheat leaves (blades and sheaths) in relation to ontogeny and soil Si availability. Results: Silicification patterns in wheat leaves varied strongly in intensity between four different growth stages (tillering, stem extension, heading, and grain filling) and ASi deposition did not just continuously increase over the growing season. Newly formed leaf tissues showed relatively low Si concentrations, which increased over time. A high condensation state of the silica bodies and trichomes was found at all growth stages, referring to a high rigidity of the silica bodies. Conclusions: Our results indicate that development of ASi deposits in wheat leaves depends on growth stage and Si availability. Detailed knowledge on solid ASi deposition in wheat during ontogeny and its consequences for stress mitigation is crucial for farmers worldwide. [ABSTRACT FROM AUTHOR]

Drought and the availability of mineable phosphorus minerals used for fertilization are two of the important issues agriculture is facing in the future. High phosphorus availability in soils is necessary to maintain high agricultural yields. Drought is one of the major threats for terrestrial ecosystem performance and crop production in future. Among the measures proposed to cope with the upcoming challenges of intensifying drought stress and to decrease the need for phosphorus fertilizer application is the fertilization with silica (Si). Here we tested the importance of soil Si fertilization on wheat phosphorus concentration as well as wheat performance during drought at the field scale. Our data clearly showed a higher soil moisture for the Si fertilized plots. This higher soil moisture contributes to a better plant performance in terms of higher photosynthetic activity and later senescence as well as faster stomata responses ensuring higher productivity during drought periods. The plant phosphorus concentration was also higher in Si fertilized compared to control plots. Overall, Si fertilization or management of the soil Si pools seem to be a promising tool to maintain crop production under predicted longer and more serve droughts in the future and reduces phosphorus fertilizer requirements. [ABSTRACT FROM AUTHOR]

Silicon (Si) accumulation is known to alleviate various biotic and abiotic stressors in plants with potential ecological consequences. However, for dicotyledonous plants our understanding of Si variation remains limited. We conducted a comparative experimental study to investigate (1) interspecific variation of foliar Si concentrations across 37 dicotyledonous forbs of temperate grasslands, (2) intraspecific variation in foliar Si concentration in response to soil Si availability, the influence of (3) phylogenetic relatedness, and (4) habitat association to moisture. Foliar Si differed markedly (approx. 70-fold) across the investigated forbs, with some species exhibiting Si accumulation similar to grasses. Foliar Si increased with soil Si availability, but the response varied across species: species with higher Si accumulation capacity showed a stronger response, indicating that they did not actively upregulate Si uptake under low soil Si availability. Foliar Si showed a pronounced phylogenetic signal, i.e., closely related species exhibited more similar foliar Si concentrations than distantly related species. Significant differences in foliar Si concentration within closely related species pairs nevertheless support that active Si uptake and associated high Si concentrations has evolved multiple times in forbs. Foliar Si was not higher in species associated with drier habitats, implying that in dicotyledonous forbs of temperate grasslands high foliar Si is not an adaptive trait to withstand drought. Our results demonstrated considerable inter- and intraspecific variation in foliar Si concentration in temperate forbs. This variation should have pervasive, but so far understudied, ecological consequences for community composition and functioning of temperate grasslands under land-use and climate change. [ABSTRACT FROM AUTHOR]

Aims: Silicon (Si) has been shown to beneficially affect plant performance under stressful environmental conditions, such as water or nutrient deficiency. Here we tested the effects of two important plant nutrients, nitrogen (N) and phosphorus (P), on Si content in different plant organs in the grass species Holcus lanatus. Methods: We studied trait responses to N limitation, balanced nutrient availability and P limitation. Single plant individuals were grown in sand-filled pots in a greenhouse for 2 months. Nitrogen, phosphorus, carbon and silicon contents were determined in leaves, stems and roots, as were leaf and roots traits, biomass production and root enzyme activity. Results: Si content was lowest under balanced nutrient supply in all plant organs. Under P limitation Si content was highest in leaves and stems, in roots it was highest under N limitation. Si:C ratios were lowest under balanced conditions, and highest under nutrient limitation. Root phosphatase activity was highest under P limitation and chlorophyll content was lowest under N limitation. Conclusions: Our model species assimilated less 'high cost C' and took up more 'low cost Si' under nutrient limitation, especially under P deficiency. Si potentially plays an important role in different environments, such as nutrient or light limitation, which in turn may be related to different plant strategies, for example higher stem rigidity in high Si plants versus higher stem flexibility in low Si plants. More research is needed to further elucidate the role of silicon in different concepts of trait-environment relationships. [ABSTRACT FROM AUTHOR]

More frequent and longer drought periods are predicted threatening agricultural yield. The capacity of soils to hold water is a highly important factor controlling drought stress intensity for plants. Biogenic amorphous silica (bASi) pools in soils are in the range of 0–6% and are suggested to help plants to resist drought. In agricultural soils, bASi pools declined to values of ~1% or lower) due to yearly crop harvest, decreasing water holding capacity of the soils. Here, we assessed the contribution of bASi to water holding capacity (WHC) of soil. Consequently, ASi was mixed at different rates (0, 1, 5 or 15%) with different soils. Afterwards, the retention curve of the soils was determined via Hyprop method. Here we show that bASi increases the soil water holding capacity substantially, by forming silica gels with a water content at saturation higher than 700%. An increase of bASi by 1% or 5% (weight) increased the water content at any water potential and plant available water increased by up to > 40% or > 60%, respectively. Our results suggest that soil management should be modified to increase bASi content, enhancing available water in soils and potentially decreasing drought stress for plants in terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Background and aim: Silicon is known to be able to substitute carbon in plant biomass, especially in cellulose, lignin and phenols. However, a more comprehensive picture regarding the effect of silicon accumulation on plant carbon quality (cellulose, lignin, phenol, wax, lipids, and free organic acids content) with regard to potential decomposability is still missing. Methods: Two different rice varieties (French brown and red rice cultivars) were cultivated under five different soil silicon availabilities. After maturity we harvested the plants and analyzed them regarding carbon quality by FTIR spectroscopy and regarding plant silicon concentrations. Results: Silicon accumulation was found to be dependent on silicon availability and on the specific rice cultivar. The lowering of carbon compounds content by silicon was found not to be restricted to cellulose, lignin and phenol. Silicon accumulation was able to decrease other carbon compounds such as fat, wax, lipids, and free organic acids, too. Conclusions: Consequently, silicon is important for the carbon quality of silicon accumulating plants. Furthermore, silicon accumulation in plants is interfering with a large range of different carbon compounds potentially altering the leaf economic spectra, decomposability, and thus potentially interfering with the whole performance of ecosystems dominated by silicon accumulating plant species. [ABSTRACT FROM AUTHOR]

Silicon (Si) has a variety of functions in plants, including alleviation of drought and light stress, defense against herbivores and pathogens, and improving plant nutrition. However, for tropical forests our knowledge about the role of silicon and its variation in soils and plants remains limited. To advance our insights into the potential role of Si in tropical forest ecology, we combined observational and experimental approaches to assess (i) variation in soluble and amorphous Si concentrations in tropical forest soils at the local and regional scale, and their relation to soil weathering stage, soil chemistry, and rainfall, (ii) variation of foliar Si concentrations across more than 30 co-occurring woody species, and (iii) intra-specific variation of foliar Si across sites and foliar habits (sun and shade). We found considerable (27-fold) variation in soluble Si (extracted in 0.01 M CaCl2) across soils, which reflected soil weathering stage and chemistry, but not rainfall. Foliar Si also varied markedly across species, both in naturally occurring trees and in a common garden experiment, with 39% of the most abundant species being classified as Si accumulators. Within species, foliar Si varied among sites and foliar habits, but relationships were inconsistent across species. The marked variability of Si concentrations in soils and leaves indicates that Si is likely to play an important yet underappreciated role for a variety of ecological processes in tropical forests. [ABSTRACT FROM AUTHOR]

The role of in-stream aquatic vegetation as ecosystem engineers in the distribution of organic matter was investigated in the Okavango Delta, one of the world's largest oligotrophic wetlands. The Okavango channel beds are covered up to 50% with submerged macrophyte patches. By accumulating and concentrating organic matter in the sediments below the patches, macrophytes are likely able to locally forestall a deficiency of nutrients. Up to 21 times more N, 18 times more C, 13 times more P and 6 times more Si can be found in vegetated sediments compared to non-vegetated sediments. Nutrient specific accumulation relates to its relative scarcity in the overlaying water. There is a depletion of dissolved N relative to P, whereas Si is relatively abundant. The Okavango Delta water can generally be characterised as oligotrophic based on plant species composition (e.g. presence of carnivorous plants and absence of floating plants), low plant N:P ratios, and low nutrient- and element-concentrations. Local mineralization and intensified nutrient cycling in the sediments is hypothesized to be crucial for the macrophytes' survival because it provides a key source of the essential nutrients which plants otherwise cannot obtain in sufficient quantities from the nutrient poor water. By engineering the ecosystem as such, channel vegetation also retards the loss of elements and nutrients to island groundwater flow, contributing to one of the key processes driving the high productivity of the Okavango Delta, making it unique among its kind. [ABSTRACT FROM AUTHOR]

Organic sediments in aquatic ecosystems are well known sinks for nutrients, silicon, and metal(loid)s. Organic matter-consuming organisms like invertebrate shredders, grazers, and bioturbators significantly affect element fixation or remobilization by changing redox conditions or binding properties of organic sediments. Little is known about the effect of filter feeders, like the zebra mussel Dreissena polymorpha , an invasive organism in North American and European freshwater ecosystems. A laboratory batch experiment exposing D . polymorpha (∼1200 organisms per m 2 ) to organic sediment from a site contaminated with arsenic, copper, lead, and uranium revealed a significant uptake and accumulation of arsenic, copper, iron, and especially uranium both into the soft body tissues and the seashell. This is in line with previous observations of metal(loid) accumulation from biomonitoring studies. Regarding its environmental impact, D . polymorpha significantly contributed to mobilization of silicon, iron, phosphorus, arsenic, and copper and to immobilization of uranium ( p < 0.001), probably driven by redox conditions, microbial activity within the gut system, or active control of element homeostasis. No net mobilization or immobilization was observed for zinc and lead, because of their low mobility at the prevailing pH of 7.5–8.5. The present results suggest that D . polymorpha can both ameliorate (nutrient mobilization, immobilization of toxicants mobile under oxic conditions) or aggravate negative effects (mobilization of toxicants mobile under reducing conditions) in ecosystems. Relating the results of the present study to observed population densities in natural freshwater ecosystems suggests a significant influence of D . polymorpha on element cycling and needs to be considered in future studies. [ABSTRACT FROM AUTHOR]

Global changes in temperature and nitrogen supply can influence key aspects of the global nutrient cycles, such as leaf litter decomposition and associated nutrient release. The effect of temperature and nitrogen supply on nutrient release during decomposition may be influenced by initial nutrient concentrations of the litter, which for grasses depends partly on silicon availability during plant growth. We conducted a five-month field experiment to test whether Phragmites australis litter silicon concentration alters the effect of climate warming and excess nitrogen supply on nutrient concentrations and litter mass loss during decomposition. Warming enhanced concentration of Ca, Mn and Fe in decomposed leaf litter, whereas excess N-supply increased the concentration of Fe and Ca in leaves. Initial Si concentrations of leaf litter influenced the stoichiometric ratios of the elements (in relation to P), and element:P ratios mostly increased for litter with intermediate and high Si concentrations, but patterns were less clear when initial litter Si concentrations were low. We show that grass litter decomposition was most strongly associated with litter Si:P, whereas C:N and N:P ratios were less important. Our results provide first evidence that global warming, enhanced N supply and changes in Si availability affect element cycling during litter decomposition. [ABSTRACT FROM AUTHOR]

Plant diversity is an important driver of nitrogen and phosphorus stocks in aboveground plant biomass of grassland ecosystems, but plant diversity effects on other elements also important for plant growth are less understood. We tested whether plant species richness, functional group richness or the presence/absence of particular plant functional groups influences the Si and Ca concentrations (mmol g) and stocks (mmol m) in aboveground plant biomass in a large grassland biodiversity experiment (Jena Experiment). In the experiment including 60 temperate grassland species, plant diversity was manipulated as sown species richness (1, 2, 4, 8, 16) and richness and identity of plant functional groups (1-4; grasses, small herbs, tall herbs, legumes). We found positive species richness effects on Si as well as Ca stocks that were attributable to increased biomass production. The presence of particular functional groups was the most important factor explaining variation in aboveground Si and Ca stocks (mmol m). Grass presence increased the Si stocks by 140 % and legume presence increased the Ca stock by 230 %. Both the presence of specific plant functional groups and species diversity altered Si and Ca stocks, whereas Si and Ca concentration were affected mostly by the presence of specific plant functional groups. However, we found a negative effect of species diversity on Si and Ca accumulation, by calculating the deviation between mixtures and mixture biomass proportions, but in monoculture concentrations. These changes may in turn affect ecosystem processes such as plant litter decomposition and nutrient cycling in grasslands. [ABSTRACT FROM AUTHOR]

The invertebrate shredder Gammarus pulex L. is a key species for aquatic carbon turnover via litter decomposition and can thrive in high-arsenic (As) environments. To understand their strategies for coping with increased As concentrations while fulfilling their ecosystem functions, we analyzed the As concentration and speciation in their aquatic habitat and in leaves with heterotrophic biofilms as their natural food source. We also followed the As distribution and speciation on the cuticle and within the body of G. pulex by X-ray absorption spectroscopic imaging. Half of the total As on G. pulex was found to be associated with the cuticle but was not taken up. Removing this externally bound As yielded only arsenate in the wash solution which reflects the speciation of the surrounding aquatic phase and shows that this As does not undergo any biotransformation. The major pathway into the organism is suggested to be incorporation via food intake, but only very low amounts of As were taken up or translocated from the gut system to other tissues. In one of the main food sources, leaves, 68% arsenate and 29% monomethylarsenate were found. After ingestion into the gut system, up to 23% of the more toxic arsenite was seen, but a substantial share was methylated to dimethylarsenate (46–56%). Little arsenate and arsenite were found in the adjacent tissues. Besides 76–80% mono- and di-methylarsenate, 10–21% of the As was complexed as As(III)–S species. G. pulex plays an important role in As cycling and our results indicate that As translocation from the gut to other tissues is minimized, but a transformation to other As-species occurred. [ABSTRACT FROM AUTHOR]

Fire can have large effects on ecosystems, with phosphorus being highly important in this regard, especially when considering productivity in burned or adjacent ecosystems after fire. Unfortunately, existing data pose contradictions and methodological challenges to assessing P availability. Here, the impact of fire on topsoil available P was estimated using three different types of organic soil layers (raw humus from spruce, humus from beech, and peat) and two fire regimes (obtaining black carbon and ash). Our findings suggest a strong fire impact on P availability, by enhancing available P during burning to black carbon (~10-fold), and to ash (~2- to 7.5-fold) dependent on calcite content. Fire impact on P availability is on a similar order of magnitude as mineral weathering and annual P cycling/ uptake in/by ecosystems. Furthermore, the proportion of available P in relation to total P depends on the origin of the organic soil layers. When related to the remaining mass after burning, as is commonly done, P availability can be overestimated by up to 1400%. Results from this study provide a realistic magnitude of shifts in P release and P availability by fire events of different intensity for widely abundant ecosystem conditions. Taking the importance of P for ecosystem processes into account, these results are highly relevant, because fires for fuel reduction are a common application, and for temperate and boreal ecosystems even moderate climate change scenarios predict an increasing appearance of fires in these regions. [ABSTRACT FROM AUTHOR]

Plant litter and organic sediments are main sinks for metals and metalloids in aquatic ecosystems. The effect of invertebrates as key species in aquatic litter decomposition on metal/metalloid fixation by organic matter is described only for shredders, but for grazers as another important animal group less is known. Consequently, a laboratory batch experiment was conducted to examine the effect of invertebrate grazers ( Lymnaea stagnalis L.) on metal/metalloid fixation/remobilization during aquatic litter decomposition. It could be shown that invertebrate grazers facilitate significantly the formation of smaller sizes of particulate organic matter (POM), as shown previously for invertebrate shredders. The metal/metalloid binding capacity of these smaller particles of POM is higher compared to leaf litter residuals. But element enrichment is not as high as shown previously for the effect by invertebrate shredders. Invertebrate grazers enhance also the mobilization of selected elements to the water, in the range also proven for invertebrate shredders but different for the different elements. Nonetheless invertebrate grazers activity during aquatic litter decomposition leads to a metal/metalloid fixation into leaf litter as part of sediment organic matter. Hence, the effect of invertebrate grazers on metal/metalloid fixation/remobilization contrasts partly with former assessments revealing the possibility of an enhanced metal/metalloid fixation. [ABSTRACT FROM AUTHOR]

Ongoing global changes, such as climate warming and increasing supply of reactive nitrogen (N), are expected to affect essential ecosystem processes such as the decomposition of plant litter. Determining the influence of environmental heterogeneity on the magnitude of these effects remains an important task, with silicon (Si) availability being a notable component of this heterogeneity, especially for grasses. We conducted an outdoor enclosure experiment to test if increased Si supply to a widespread foundation species (.Phragmites australis) alters the effect of climate warming and excess N supply on litter decomposition by curbing fungal decomposers. Consistent with expectations, Si supply during plant growth reduced fungal biomass in decomposing leaf blades by 50%, an effect that was doubled by excess external N supply. These strong impacts, however, did not directly translate to reduced litter decomposition or associated changes in nutrient dynamics. Instead, plant tissue-specific effects determined the influence of Si, N, and elevated temperature on litter mass loss. Specifically, Si accelerated the decomposition of leaf sheaths, warming enhanced leaf-sheath and leaf-blade decomposition, and N decreased the decomposition of culm litter, in line with expectations based on differences in litter chemistry. Thus, despite highly detrimental effects of Si and N on fungal decomposers, compensation by other members of the microbial community could dampen the realized impact of these global-change factors on the decomposition of plant litter in the future. [ABSTRACT FROM AUTHOR]

Shortages of resources (chemical elements) used by growing industrial activities require new techniques for their acquisition. A suitable technique could be the use of wetlands for the enrichment of elements from produced water of the oil industry. Oil industries produce very high amounts of water in the course of oil mining. These waters may contain high amounts of rare elements. To our best knowledge nothing is known about the economic potential regarding rare element mining from produced water. Therefore, we estimated the amount of harvestable rare elements remaining in the effluent of a constructed wetland-pond system which is being used to treat and evaporate vast quantities of produced waters. The examined wetland system is located in the desert of the south-eastern Arabian Peninsula. This system manages 95,000 m³ per day within 350 ha of surface flow wetlands and 350 ha of evaporation ponds and is designed to be used for at least 20 years. We found a strong enrichment of some chemical elements in the water pathway of the system (e.g. lithium up to 896 µg L-1 and beryllium up to 139 µg L-1). For this wetland, lithium and beryllium are the elements with the highest economic potential resulting from a high price and load. It is calculated that after 20 years retention period 131 t of lithium and 57 t of beryllium could be harvested. This technique may also be useful for acquisition of rare earth elements. Other elements (e.g. strontium) with a high calculated load of 4500 tons in 20 years are not efficiently harvestable due to a relatively low market value. In conclusion, wetland treated waters from the oil industry offer a promising new acquisition technique for elements like lithium and beryllium. [ABSTRACT FROM AUTHOR]

Highlights: [•] Chironomus plumosus has a main impact on elemental mobilization from sediments. [•] DOC, N, Mg, Ca, Sr, Mo and U were highly influenced by bioturbation/bioirrigation. [•] Al, Fe, Co, Cu, Zn and Ce were affected only at start (larvae dig into sediments). [•] Mn, Ni, As, Cd and Cs mobilization were affected at start and slightly afterwards. [•] Invertebrate bioturbation/bioirrigation is a main process in element cycling. [Copyright &y& Elsevier]

Iron and manganese are relevant constituents of the earth's crust and both show increasing mobility when reduced by free electrons. This reduction is known to be controlled by microbial dissimilation processes. Alternative sources of free electrons in nature are cloud-to-ground lightning events with thermal and galvanic effects. Where thermal effects of lightning events are well described, less is known about the impact of galvanic lightning effects on metal mobilization. Here we show that a significant mobilization of manganese occurs due to galvanic effects of both positive and negative lightning, where iron seems to be unaffected with manganese being abundant in oxic forms in soils/sediments. A mean of 0.025 mmol manganese (negative lightning) or 0.08 mmol manganese (positive lightning) mobilization may occur. We suggest that lightning possibly influences biogeochemical cycles of redox sensitive elements in continental parts of the tropics/subtropics on a regional/local scale. [ABSTRACT FROM AUTHOR]

The decomposition rate of plant litter is important for the carbon cycle. Element stoichiometry and hardly degradable carbon compounds are main factors controlling the decomposition rate of plant litter. Recent research has linked these factors to silicon availability during plant growth, but no research focused on the effect of silicon on litter decomposition. We therefore conducted a batch experiment to assess the effect of silicon availability to plants on litter degradation, nutrient release and multi elemental stoichiometry. Experiments were conducted in the presence or absence of invertebrate shredders ( Gammarus pulex). We show that nutrient content (affected by silicon availability during plant growth) has a strong impact on nutrient turnover, while DOC, N, and Mn were mainly controlled by invertebrate feeding. The carbon turnover during microbial litter decay was strongly influenced by the silicon availability during plant growth, with quicker potential C turnover of litter with higher silicon content. In both Si-rich and Si-poor litter, feeding by invertebrate shredders positively impacted turnover rates, but effects were less pronounced in Si-rich litter. It can be concluded that silicon availability in wetlands dominated by reed plays an important role in carbon sequestration, nutrient cycling, and remobilization during aquatic litter decay. [ABSTRACT FROM AUTHOR]

UV-screening by terrestrial plants is a crucial trait since colonization of terrestrial environments has started. In general, it is enabled by phenolic substances. Especially for grasses it remains unclear why plants grown under the absence of UV-B-radiation exhibit nonetheless a high UV-B-screening potential. But this may be explained by the UV-screening effect of the silicon double layer. It was shown for seedlings of soybeans ( Glycine max L.) and wheat ( Triticum aestivum L.) that enhanced silicon supply reduces stress induced by UV-radiation. Even more important is a direct correlation between silicon content in the epidermis near area (intercellular spaces) and the absorption of UV-radiation in this area shown in other papers. The silicon double layer may act like a glass layer and decreases the transmission of UV-radiation at the epidermis near area. In summary, the absorbance/reflection of ultraviolet radiation is dependent on the characteristics of the epidermis near area of leaves, particularly the occurrence (qualitatively and quantitatively) of phenolic substances and/or a silicon double layer in this area. Consequently, UV-screening by plant silicon double layer should get more attention in future research with emphasis on effects of UV-radiation on plant physiology. [ABSTRACT FROM AUTHOR]

Abstract: Increasing arsenic concentrations in freshwater ecosystems is of global concern. Processes affecting arsenic fluxes in catchments are known. These processes are in turn controlled by the underlying geology and air pollution history. In contrast to the knowledge on catchment processes less is known about the hydrochemical processes controlling the fixation/remobilization of arsenic within lakes and artificial reservoirs. Consequently, we examined a reservoir system in the Ore Mts. (Germany) regarding its sink and source potentials affecting arsenic fluxes. This area was faced with heavy deposition inputs from coal burning based acid rain until the beginning of the 1990s. Hereafter concentrations of sulfate and nitrate in runoff waters decreased, whereas dissolved organic carbon (DOC) concentrations are still increasing. Along with this, arsenic concentrations in the water discharge from the catchments increase. Our results reveal that the sediments of the investigated reservoir system contain high inventories of arsenic in association with ferric and organic phases. A nitrate deficit dependent arsenic release is suggested. It is indicated that arsenic release from the reservoir sediments may be controlled by water nitrate concentration, which in turn is dependent on the nitrate concentration in the runoff water from the catchment. [Copyright &y& Elsevier]

Abstract: Wetlands are well known for water treatment and as a sink for elements (e.g. metals/metalloids). The elements are mainly fixed by sediments, microbial biofilms and plants, whereas the organic part of the sediment has a potential important role. These organic sediments underlie the process of organic matter decomposition, which proceeds in the three distinct steps of leaching, microbial conditioning and fragmentation by aquatic fauna. The effect of organic matter fragmentation on elemental fixation was shown previously only under neutral pH conditions. Hence, a batch experiment was conducted to assess the effect of invertebrate shredder on elemental accumulation during litter decay under low acidic conditions. Here it is shown that this fragmentation of the organic material by aquatic fauna enhances the elemental fixation potential of the organic sediments significantly, also under low acidic conditions. During the process of fragmentation the surface area of the organic matter increases by increasing amount of smaller particles. This in turn results in higher adsorption capacity of a larger amount of growing biofilm enhancing the surface even more (heterotrophic microorganisms). The growing biofilm (periphyton) with its larger surface area and hence more functional groups result in higher elemental fixation. Therefore, invertebrate shredders as ecosystem engineers enhance the capability for elemental fixation by fragmentation of organic matter, which is an important process in wetlands ecosystems usable in a broad pH range. [Copyright &y& Elsevier]

Abstract: The rapid increase of shortages in resources of chemical elements (and ores) used for an increasing industrial production raises the question of alternative strategies for their acquisition. Simultaneously, the elemental load in aquatic ecosystems increases by anthropogenic activities. Polluted waters are purged actively by technical treatment plants or passively by wetlands. Wetlands are known to eliminate/fix pollutants with a potentially high efficiency. Regarding this elimination/fixation potential less is known about different types of wetlands for elemental recovery. This paucity of information prompted to us to assess the impact of main processes in different types of wetlands on the recovery potential of chemical elements showing advantages and disadvantages of autochthonous and allochthonous wetlands and possible solutions. We show that autochthonous as well as allochthonous wetlands are able to accumulate high amounts of elements, but it is suggested that combining autochthonous/allochthonous processes should result in a higher efficiency. [Copyright &y& Elsevier]

Abstract: Organic matter is known to accumulate high amounts of metals/metalloids, enhanced during the process of decomposition by heterotrophic biofilms (with high fixation capacity for metals/metalloids). The colonization by microbes and the decay rate of the organic matter depends on different litter properties. Main litter properties affecting the decomposition of organic matter such as the nutrient ratios and the content of cellulose, lignin and phenols are currently described to be changed by silicon availability. But less is known about the impact of silicon availability during plant growth on elemental fixation during decay. Hence, this research focuses on the impact of silicon availability during plant growth on fixation of 42 elements during litter decay, by controlling the litter properties. The results of this experiment are a significantly higher metal/metalloid accumulation during decomposition of plant litter grown under low silicon availability. This may be explained by the altered litter properties (mainly nutrient content) affecting the microbial decomposition of the litter, the microbial growth on the litter and possibly by the silicon double layer, which is evident in leaf litter with high silicon content and reduces the binding sites for metals/metalloids. Furthermore, this silicon double layer may also reduce the growing biofilm by reducing the availability of carbon compounds at the litter surface and has to be elucidated in further research. Hence, low silicon availability during plant growth enhances the metal/metalloid accumulation into plant litter during aquatic decomposition. [Copyright &y& Elsevier]

Abstract: Silicon is described as beneficial for grasses by enhancing yield and fitness via a considerable contribution to pathogen, drought, and pest resistance. Silicic acid is the predominant form for uptake and transport within the plant and will precipitate in leaves. But it is unknown whether polymeric nanosilicon compounds in its synthetic form, with an increasing concentration in aquatic environments, can be suitable for plant nutrition. Therefore, we investigated the uptake, transport, and deposition of silicic acid/silica within plants using synthetic nanosilica. Our results show a significant difference in silicon (Si) content within the different tissues of Phragmites australis. The nanosilica had been dissolved prior to the uptake by plants. The chemical form of Si during uptake was not traceable. A significant enhancement in the condensation state of the silica was found from root to leaves especially from culm to leaf tips visible by the increasing content of Q4-groups in the NMR spectra. We conclude that synthetic nanosilica has the same quality as source for the beneficial element Si like natural silica. Since the condensation state is described to control silica solubility, we suggest that different condensation states within the plant may result in different remobilization of silicon during decomposition of the plant material. [Copyright &y& Elsevier]

Abstract: Background: Experimental tonic pain has been assumed to equal clinical pain by triggering sizeable affective responses. A psycho-physiological indicator of defensive affective-motivational responses is the startle reflex. However, earlier studies have not provided unequivocal evidence for a potentiation of the startle reflex during tonic contact heat pain. Objectives: The demonstration of modulating effects of pain on the startle reflex might require very intense tonic stimulation and investigation of subjects, who are particularly sensitive to startle potentiation by threatening cues. Method: We investigated a sample of healthy subjects (N=20), who had shown pronounced startle amplitude potentiation in response to attack pictures. Noxious stimulation was provided by hand immersion into a hot water bath, which is a tonic pain model known for intense and summated stimulation. Modulation of the startle reflex was attempted by use of two stimulation intensities (42°C, 46°C) and one control condition (no stimulation). Results: Even in these favorable conditions, we did not observe startle potentiation under painful stimulation in comparison to non-painful conditions although subjects reported to be experiencing moderate to high pain. Conclusions: Our findings indicate that tonic heat pain does not trigger defensive affective-motivational responses as measured by the startle reflex when it is applied in a predictable and thus non-threatening fashion. Future research should investigate the effects of manipulations of threat on startle responses to painful stimulation. [Copyright &y& Elsevier]

Abstract: Silicon is not an essential element in sensu stricto but affects the productivity of Poaceae. Recent field studies has shown the effect of silicon on cellulose and lignin content in bulk analyses of green compartments of different species, sampled before matter translocation in the course of senescence. Nevertheless, there is a gap in information about silicon availability and its effect on cellulose, lignin and phenol content in different plant tissues after nutrient resorption. In order to prove the effect of controlled silica supply on functional relevant carbon compounds Phragmites australis Trin. was grown in pot trials under three different levels of silicon surplus. After resorption of nutrients into rhizomes the content of silicon, lignin, cellulose and phenol were measured in different plant tissues. The results show that different levels of silicon surplus changed the plant cellulose, lignin and phenol content depending on plant tissue function. Cellulose content in tissues with stabilization function is reduced contrasting enhanced cellulose content in tissues without stabilization function. Furthermore, higher silicon surplus decreased the phenol content in photosynthetic active tissues and increased the phenol content in culm. Only weak silicon to lignin interaction was found. It is concluded that silicon affects the cellulose and phenol metabolism and the tradeoff between productivity and stabilization/defense. Considering these compounds as crucial factors in decay processes, silicon may be very important for the terrestrial and semi-terrestrial carbon turnover [Copyright &y& Elsevier]

Abstract: Soil aggregation is a principal ecosystem process mediated by soil biota. Collembola and arbuscular mycorrhizal (AM) fungi are important groups in the soil, and can interact in various ways. Few studies have examined collembola effects on soil aggregation, while many have quantified AM effects. Here, we asked if collembola have any effect on soil aggregation, and if they alter AM fungi-mediated effects on soil aggregation. We carried out a factorial greenhouse study, manipulating the presence of both collembola and AM fungi, using two different plant species, Sorghum vulgare and Daucus carota. We measured root length and biomass, AMF (and non-AMF) soil hyphal length, root colonization, and collembolan populations, and quantified water stable soil aggregates (WSA) in four size classes. Soil exposed to growth of AMF hyphae and collembola individually had higher WSA than control treatments. Moreover, the interaction effects between AMF and collembola were significant, with non-additive increases in the combined application compared to the single treatments. Our findings show that collembola can play a crucial role in maintaining ecological sustainability through promoting soil aggregation, and point to the importance of considering organism interactions in understanding formation of soil structure. [Copyright &y& Elsevier]

Abstract: The focus of this article is to combine two main areas of research activities in freshwater ecosystems: the effect of inorganic pollutants on freshwater ecosystems and litter decomposition as a fundamental ecological process in streams. The decomposition of plant litter in aquatic systems as a main energy source in running water ecosystems proceeds in three distinct temporal stages of leaching, conditioning and fragmentation. During these stages metals and metalloids may be fixed by litter, its decay products and the associated organisms. The global-scale problem of contaminated freshwater ecosystems by metals and metalloids has led to many investigations on the acute and chronic toxicity of these elements to plants and animals as well as the impact on animal activity under laboratory conditions. Where sorption properties and accumulation/remobilization potential of metals in sediments and attached microorganisms are quite well understood, the combination of both research areas concerning the impact of higher trophic levels on the modification of sediment sorption conditions and the influence of metal/metalloid pollution on decomposition of plant litter mediated by decomposer community, as well as the effect of high metal load during litter decay on organism health under field conditions, has still to be elucidated. So far it was found that microbes and invertebrate shredder (species of the genera Gammarus and Asellus) have a significant influence on metal fixation on litter. Not many studies focus on the impact of other functional groups affecting litter decay (e.g. grazer and collectors) or other main processes in freshwater ecosystems like bioturbation (e.g. Tubifex, Chironomus) on metal fixation/release. [Copyright &y& Elsevier]

Abstract: Organic-rich sediments are known to be effective accumulators for uranium and arsenic. Much is known about the capacity for metal or metalloid fixation by microbes and organic compounds as well as inorganic sediment particles. Experiments investigating the effect of microbes on the process of metal fixation in sediments require sterilized sediments as control treatment which is often realized by gamma-sterilization. Only few studies show that gamma-sterilization has an effect on the remobilization of metal and metalloids and on their physico-chemical properties. These studies deal with sediments with negligible organic content whereas almost nothing is known about organic-rich sediments including a probably high microbial activity. In view of this, we investigated the effect of gamma-sterilization of organic-rich sediments on uranium and arsenic fixation and release. After ten days within an exposure experiment we found a significant higher remobilization of uranium and arsenic in sterile compared to unsterile treatments. In line with these findings the content of dissolved organic carbon (DOC), manganese, and iron increased to even significantly higher concentration in the sterile compared to unsterile treatment. Gamma-sterilization seems to change the physico-chemical properties of organic-rich sediments. Microbial activity is effectively eliminated. From increased DOC concentrations in overlaying water it is concluded that microbes are eventually killed with leaching of cellular compounds in the overlaying water. This decreases the adsorption capacity of the sediment and leads to enhanced uranium and arsenic remobilization. [Copyright &y& Elsevier]

Abstract: Invertebrate shredders such as Gammarus pulex are key species in contaminated stream ecosystems. Although a number of previous studies examining differences in metal accumulation between the gut system and remaining tissues of invertebrates exist, few focus on wide range of metals and metalloids that are relevant to contaminated systems. This study compared accumulation of the commonest (at study site) 15 metals and metalloids between the gut system including feces and remaining tissues of G. pulex. All metals and metalloids measured were significantly higher (p <0.001, except Cu p <0.005) in the gut system including feces than remaining tissues of G. pulex. Metals and metalloids in body tissues without the gut system including feces were significantly lower (Al, Cr, Fe and Mn (p <0.005), Sr and U (p <0.01), Co (p <0.05)) in content for a number of elements when compared to washed, whole G. pulex specimens. As well, all elements measured were significantly higher (all elements (p <0.005) except Cu and Co (p <0.05)) in gut system including feces than washed, whole G. pulex specimens. These results indicate that in G. pulex the uptake of all 15 metals and metalloids examined across the gut epithelium is minimalized or that sequestration of these elements in gut epithelial cells may occur. [Copyright &y& Elsevier]

Microcystic adnexal carcinoma (MAC) is a rare, usually solitary, slowly growing, yet aggressive neoplasm with a tendency for local recurrences. Herein, we present two patients who had been histopathologically diagnosed as suffering from MAC on both cheeks since childhood, an unlikely scenario. Both from a clinical and from a histopathological point of view, our two cases showed some similarities with those previously described in patients with Nicolau-Balus syndrome, Rombo syndrome, and so-called eccrine-pilar hamartoma. Common to all these latter disorders are the round aggregations of elastic tissue in the papillary dermis, a histopathological feature which was also found in our patients. However, to our knowledge, the presence of a MAC-like ductal proliferation embedded in sclerotic stroma and extending to the deep dermis has not been previously described. Dermatologists and dermatopathologists should be aware of this disorder to avoid overdiagnosis of and inappropriate treatment for MAC. Schaller J, Rytina E, Rütten A, Hendricks C, Ha T, Requena L. Sweat duct proliferation associated with aggregates of elastic tissue and atrophodermia vermiculata: a simulator of microcystic adnexal carcinoma. Report of two cases. [ABSTRACT FROM AUTHOR]

The authors report a case of Brooke-Spiegler syndrome (BSS) with a novel germline CYLD mutation and various somatic mutations identified in the lesional tissues. The patient was a 46-year-old man with multiple lesions on the face. The available histopathological material included 24 trichoepitheliomas, 2 large nodular basal cell carcinomas (BCCs), 2 spiradenomas, 1 spiradenocylindroma and 1 trichoblastoma composed of large and small nodules with prominent clear cell differentiation. Whereas one of the two BCCs manifested a conventional morphology, the second neoplasm additionally showed foci with high grade cytological features characterized by marked pleomorphism and numerous mitotic figures. There were also numerous signet ring cells and cells containing intracytoplasmic eosinophilic inclusions. The germline mutation was a substitution mutation c.1684 + 1G> A. Somatic mutations were investigated in eight tissue blocks from which high quality genomic DNA had been successfully extracted. Somatic mutations included loss of heterozygosity (LOH) in four lesions and a single sequence mutation, namely a single base deletion c. 2322delA causing a frameshift mutation E774DfsX2. LOH occurred in both BCCs, one trichoepithelioma and one spiradenoma. In the remaining three lesions, the somatic event remained undetected. Kazakov DV, Schaller J, Vanecek T, Kacerovska D, Michal M. Brooke-Spiegler syndrome: report of a case with a novel mutation in the CYLD gene and different types of somatic mutations in benign and malignant tumors. [ABSTRACT FROM AUTHOR]

Abstract: Organic sediments are known to be a significant sink of inorganic elements in polluted freshwater ecosystems. Hence, we investigated the role of invertebrate shredders (the freshwater shrimp Gammarus pulex L.) in metal and arsenic enrichment into organic partitions of sediments in a wetland stream at former uranium mining site. Metal and metalloid content in leaf litter increased significantly during decomposition, while at the same time the carbon content decreased. During decomposition, G. pulex as a ecosystem engineer facilitated significantly the enrichment of magnesium (250%), manganese (560%), cobalt (310%), copper (200%), zinc (43%), arsenic (670%), cadmium (100%) and lead (1340%) into small particle sizes. The enrichments occur under very high concentrations of dissolved organic carbon. Small particles have high surface area that results in high biofilm development. Further, the highest amounts of elements were observed in biofilms. Therefore, invertebrate shredder like G. pulex can enhance retention of large amounts of metal and arsenic in wetlands. [Copyright &y& Elsevier]

Plant litter and organic matter of aquatic sediments provide a significant sink of soluble inorganic uranium species in contaminated ecosystems. The uranium content in detritus has been observed to increase significantly during decomposition. However, the influence of the decomposer community on uranium fixation remains unclear. In view of this, we investigated the influence of a shredder (the freshwater shrimp Gammarus pulex L) on uranium fixation and mobilization during the degradation of plant litter. Leaf litter from Alnus glutinosa (L) Gaertn with 1152 mg kg-1 U of dry biomass (DM) and without uranium was used in a 14-day laboratory experiment. The uranium concentration in the particulate organic material (POM) at the end of experiment was 1427 mg kg-1 DM. After 14 days of decay, the residues of the leaves show a uranium concentration of 644 mg kg-1 DM. Uranium concentrations in the media initially increased reaching up to 63.9 μg L-1 but finally decreased to an average value of 34.3 μg L-1. At the same time, DOC levels increased from 2.43 mg L-1 up to 11.4 mg L-1 in the course of the experiment Hence, inorganic uranium fixation onto particulate organic matter was enhanced by the activity of G. pulex. [ABSTRACT FROM AUTHOR]

• Heat effects form fire potentially plays an important role in global Si cycling. • Heat increased Si availability up to ~700% in different mineral soils. • Heat increased amorphous Si up to 1.9 × 104% in these soils. Altered fire regimes as a response to climate change are significantly affecting terrestrial ecosystems and biogeochemical cycles. In this context, not only natural fires but also anthropogenic fires like rice straw burning have to be considered. While heat effects of fire on some nutrient cycles (e.g., carbon, nitrogen, phosphorus) have been well-studied, little is known about consequences of heat for the silicon (Si) cycle. There is some information that heat increases the release of Si from soil organic matter. However, nothing is known about the effect of heat on Si availability in mineral soils to the best of our knowledge. We analyzed the effect of heat on Si availability in six different mineral soils. Our data show that heat is increasing Si availability (Mehlich-3 extractable) of all tested soils. The same pattern was found for amorphous Si (alkaline extraction) for most of these soils. Consequently, heated soils might represent a strong and immediate source for plant available Si. Ecosystem characteristics (e.g., vegetation, soil type) that affect uptake-leaching balances determine the further fate of the released Si. In summary, heat might affect Si cycling not only by strongly increasing Si availability in soil organic matter but also in mineral soils. [ABSTRACT FROM AUTHOR]

There is increased interest in the terrestrial silicon cycle in the last decades as its different compounds and species have large implications for ecosystem performance in terms of soil nutrient and water availability, ecosystem productivity as well as ecological aspects such as plant–microbe and plant-animal feedbacks. The currently existing analytical methods are limited. Fourier-transform infrared spectroscopy (FTIR) analysis is suggested being a promising tool to differentiate between the different Si species. We report here on the differentiation of varying Si-species/Si-binding (in synthetic material) using FTIR-analyses. Therefore, we collected FTIR-spectra of five different amorphous silica, Ca-silicate, sodium silicate (all particulate), a water-soluble fraction of amorphous silica and soil affected by volcanic activity and compared their spectra with existing data. A decrease of the internal order of the materials analyzed was indicated by peak broadening of the Si–O–Si absorption band. Peak shifts at this absorption band were induced by larger ions incorporated in the Si–O–Si network. Additionally, short-range ordered aluminosilicates (SROAS) have specific IR absorption bands such as the Si–O–Al band. Hence, SROAS and Si phases containing other ions can be distinguished from pure amorphous Si species using FTIR-analyses. [ABSTRACT FROM AUTHOR]

Predicted climate warming and prolonged droughts pose a threat to the soil structure as organic carbon losses weaken the stability of soil aggregates. Well-structured soils are important for storage and movement of water, solutes, and air, the development of plant roots, as habitat for soil organisms, and the microbial activity. Structural stability is measured in terms of hydro-mechanical properties. This study compares effects of amorphous silica with those of organic carbon on stability parameters during drying of aggregates from relatively finer- and coarser-textured soils. Silica amendment enhanced the positive effect of organic carbon on structural stability in terms of the tensile strength. Synergistic effects between silica and organic carbon in soil colloids appear to dynamically alter aggregate density and friability (i.e., ability to crumble) during drying. Silica together with organic carbon could help soil management to reduce negative effects of predicted prolonged droughts on soil structure and stability. [ABSTRACT FROM AUTHOR]

Various studies showed a decrease of drought stress specific parameters of plants after silicon (Si) fertilization. But all studies differed in soil Si concentration between the control and Si treatments. As amorphous silica (ASi) was recently found to cause a strong increase of water holding capacity and plant available water in soils, a combined effect of soil moisture and plant response due to Si addition was assumed. In this study, the influence of the soil Si content was excluded by using the same Si enriched soil for treatments of two rice lines, lsi1 mutant defective in Si uptake and its wild‐type rice. Most plant parameters, such as nutrient contents, biomass, specific leaf area, specific root length, leaf water content and C allocation did not differ significantly between the genotypes neither under flooded conditions, nor under drought conditions. Only photosynthesis and stomatal conductance were slightly higher for the wild type in both drought and flooded treatments. Overall, our data showed that Si accumulation within the plant tissues has only a minor effect on plant performance under drought stress. Hence, existing studies should be reinterpreted in light of the fact that Si additions may increase soil water availability. Our data shows that the effect of Si‐fertilization on mitigating drought stress for plants may be less via effects in planta but rather by Si‐fertilization increasing soil water availability to plants. [ABSTRACT FROM AUTHOR]

Phosphorus availability in soils is an important parameter influencing primary production in terrestrial ecosystems. Phosphorus limitation exists in many soils since a high proportion of soil phosphorus is stored in unavailable forms for plants, such as bound to iron minerals or stabilized organic matter. This is in spite of soils having a high amount of total soil phosphorus. The feasibility of silicon to mobilize phosphorus from strong binding sites of iron minerals has been shown for marine sediments but is less well studied in soils. Here we tested the effect of silicon on phosphorus mobilization for 143 Artic soils (representing contrasting soil characteristics), which have not been affected by agriculture or other anthropogenic management practices. In agreement with marine studies, silicon availabilities were significantly positive correlated to phosphorus mobilization in these soils. Laboratory experiments confirmed that silicon addition significantly increases phosphorus mobilization, by mobilizing Fe(II)-P phases from mineral surfaces. Silicon addition increased also soil respiration in phosphorus deficient soils. We conclude that silicon is a key component regulating mobilization of phosphorous in Arctic soils, suggesting that this may also be important for sustainable management of phosphorus availability in soils in general. [ABSTRACT FROM AUTHOR]

Soil water holding capacity (WHC) is a key soil property determining water availability to plants. Plants increase the organic carbon content of soils, depending on the amount and quality of litter, and with this affect the WHC. Plants accumulate also high amounts of amorphous silica (ASi) of calcium oxalate (Ca-ox) in their tissues. After plant tissues are deposited in the soil, this results in elevated concentrations of these compounds in soils. ASi content in soils range between 0 and 6%. It was suggested that agricultural practice (yearly export of biomass) leads to a strong decrease of ASi content in soils. We tested the effect of biogenic (plant derived) ASi on soil water holding capacity. We found that biogenic ASi forms silica gels with WHC > 700% and it increases soil WHC to values similar to those of clay minerals. An increase of biogenic ASi pools by 5% enhances soil WHC by >15%. Biogenic ASi (mostly phytoliths) can be preserved in soils for many years (as biogenic ASi) until Si is mobilized to dissolved silica DSi by phytolith dissolution. Increasing DSi content in soils slightly decreases the soil WHC. However, high DSi contents favor neoformation of clay minerals, which have high WHC. WHC of soils with 5% biogenic ASi content is higher than soils with 5% montmorillonite, a mineral of the fine clay fraction, known to be responsible for large parts of WHC. Consequently, the speciation of Si is highly important because it determines the WHC of soils. Additionally, we analyzed the effect of Ca-ox on WHC. Increasing soil Ca-ox content increases WHC, especially under negative water potentials. However, for common values of Ca-ox in soils (<1%) Ca-ox effects on soil WHC are negligible. In summary, we propose that preserving the biogenic ASi content in soils should be a target of agricultural practices that aim at increasing WHC and reducing the negative effects of drought on crops. [ABSTRACT FROM AUTHOR]

Rice straw increasingly remains on the fields for nutrient supply to the next generation of crop plants. It can be applied either fresh or after burning to black carbon or ash. A central concern during rice cultivation is accumulation of carcinogenic arsenic and the question arises how much rice straw application contributes to nutrient versus arsenic supply in paddy fields. Laboratory incubation experiments were performed to assess the effect of rice straw, black carbon and ash on element mobilization. Our experiments showed initially higher silicon and phosphorus release from black carbon compared to fresh straw amendments. However, more re-sorption to soil lead to finally slightly lower pore water concentrations for black carbon versus fresh straw amendments. Highest arsenic, iron, manganese and dissolved organic carbon concentrations were observed after fresh rice straw application. Black carbon and ash application lead to only minor increases of arsenic compared to controls without amendments. Overall, for silicon and phosphorus the soil acts as sink while for iron and arsenic it was the main source. In summary, burning of rice straw to black carbon prior to application seems to yield a high increase in desired nutrient and a decrease in undesired arsenic mobilization in paddy soils. [ABSTRACT FROM AUTHOR]

Plant monocultures growing for extended periods face severe losses of productivity. This phenomenon, known as 'yield decline', is often caused by the accumulation of above‐ and below‐ground plant antagonists. The effectiveness of plant defences against antagonists might help explain differences in yield decline among species. Using a trait‐based approach, we studied the role of 20 physical and chemical defence traits of leaves and fine roots on yield decline of 4‐ and 18‐year‐old monocultures of 27 grassland species. We hypothesized that yield decline is lower for species with high defences, that root defences are better predictors of yield decline than leaf defences, and that in roots, physical defences better predict yield decline than chemical defences, while the reverse is true for leaves. We additionally hypothesized that the relationship between defences and yield decline increases with time and that species increasing the expression of defence traits after long‐term monoculture growth would suffer less yield decline. We summarized leaf and fine root defence traits using principal component analyses and analysed the relationship between the most informative components along with their temporal changes and monoculture yield decline. The significant predictors of yield decline were traits related to the so‐called collaboration gradient of the root economics space (specific root length and root diameter) as well as their temporal changes and traits related to the leaf physical vs chemical defence tradeoff (leaf dry matter, silicon and cellulose content, toughness and phytochemical diversity). We were unable to unequivocally identify the mechanisms relating the effect of those traits to yield decline as they could mediate plant responses to several stressors such as antagonist accumulation, nutrient depletion or drought. Further studies are needed to differentiate between these alternative mechanisms and to gain a comprehensive understanding of the drivers of yield decline in relation to root and leaf defence traits. [ABSTRACT FROM AUTHOR]

Silicon (Si) is known as beneficial element for graminaceous plants. The importance of Si for plant functioning of cereals was recently emphasized. However, about the effect of Si availability on biomass production, grain yield, nutrient status and nutrient use efficiency for wheat (Triticum aestivum L.), as one of the most important crop plants worldwide, less is known so far. Consequently, we assessed the effect of a broad range of supply levels of amorphous SiO2 on wheat plant performance. Our results revealed that Si is readily taken up and accumulated basically in aboveground vegetative organs. Carbon (C) and phosphorus (P) status of plants were altered in response to varying Si supply. In bulk straw biomass C concentration decreased with increasing Si supply, while P concentration increased from slight limitation towards optimal nutrition. Thereby, aboveground biomass production increased at low to medium supply levels of silica whereas grain yield increased at medium supply level only. Nutrient use efficiency was improved by Si insofar that biomass production was enhanced at constant nitrogen (N) status of substrate and plants. Consequently, our findings imply fundamental influences of Si on C turnover, P availability and nitrogen use efficiency for wheat as a major staple crop. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article on the role of teicoplanin for outpatient parenteral antibiotic therapy (OPAT) for bone and joint infections (BJI)," by Mackintosh and colleagues.