Near-infrared spectroscopy (NIRS) is a high-throughput technology with potential to infer nitrogen (N), phosphorus (P) and carbon (C) content of all vascular plants based on empirical calibrations with chemical analysis, but is currently limited to the sample populations upon which it is based. Here we provide a first step towards a global arctic-alpine NIRS model of foliar N, P and C content. We found calibration models to perform well (R2validation = 0.94 and RMSEP = 0.20% for N, R2validation = 0.76 and RMSEP = 0.05% for P and R2validation = 0.82 and RMSEP = 1.16% for C), integrating 97 species, nine functional groups, three levels of phenology, a range of habitats and two biogeographic regions (the Alps and Fennoscandia). Furthermore, when applied for predicting foliar N, P and C content in samples from a new biogeographic region (Svalbard), our arctic-alpine NIRS model performed well. The precision of the resulting NIRS method meet international requirements, indicating one NIRS measurement scan of a foliar sample will predict its N, P and C content with precision according to standard method performance. The modelling scripts for the prediction of foliar N, P and C content using NIRS along with the calibration models upon which the predictions are based are provided. The modelling scripts can be applied in other labs, and can easily be expanded with data from new biogeographic regions of interest, building the global arctic-alpine model.

Silicon (Si) is one of the most common elements in the earth bedrock, and its continental cycle is strongly biologically controlled. Yet, research on the biogeochemical cycle of Si in ecosystems is hampered by the time and cost associated with the currently used chemical analysis methods. Here, we assessed the suitability of Near Infrared Reflectance Spectroscopy (NIRS) for measuring Si content in plant tissues. NIR spectra depend on the characteristics of the present bonds between H and N, C and O, which can be calibrated against concentrations of various compounds. Because Si in plants always occurs as hydrated condensates of orthosilicic acid (Si(OH)4), linked to organic biomolecules, we hypothesized that NIRS is suitable for measuring Si content in plants across a range of plant species. We based our testing on 442 samples of 29 plant species belonging to a range of growth forms. We calibrated the NIRS method against a well-established plant Si analysis method by using partial least-squares regression. Si concentrations ranged from detection limit (0.24 ppmSi) to 7.8% Si on dry weight and were well predicted by NIRS. The model fit with validation data was good across all plant species (n = 141, R (2) = 0.90, RMSEP = 0.24), but improved when only graminoids were modeled (n = 66, R (2) = 0.95, RMSEP = 0.10). A species specific model for the grass Deschampsia cespitosa showed even slightly better results than the model for all graminoids (n = 16, R (2) = 0.93, RMSEP = 0.015). We show for the first time that NIRS is applicable for determining plant Si concentration across a range of plant species and growth forms, and represents a time- and cost-effective alternative to the chemical Si analysis methods. As NIRS can be applied concurrently to a range of plant organic constituents, it opens up unprecedented research possibilities for studying interrelations between Si and other plant compounds in vegetation, and for addressing the role of Si in ecosystems across a range of Si research domains.

QuestionHow does the interaction between silicon (Si) and vegetation affect local and global ecological processes, higher levels of ecological organization, and terrestrial- and watershed-scale Si fluxes?LocationWe selected several ecosystems throughout the world, from river headwaters to estuaries, being examples of (i) terrestrial vegetation, (ii) aquatic and floodplain vegetation, and (iii) tidal wetland vegetation.MethodsWe provide examples of the importance of linking Si use by terrestrial and aquatic vegetation, to larger-scale Si flux consequences towards and through rivers. Cross-disciplinary studies achieve the best understanding of vegetation effects on the global Si cycle, and the role of Si as a plant functional trait.ConclusionSi use by plants has not always received the research attention of other elements. Yet, today the importance of Si for plant functioning is slowly becoming better understood. Silicon is a crucial element for many plant species, being important for decomposition processes, plant competitiveness and stress tolerance. The inclusion by vegetation scientists of Si uptake as a plant functional trait is important to assess links between plant physiology, plant distribution and plant tolerance to environmental changes, but also to understand the role of vegetation on Si fluxes through the watershed. However, lack of knowledge regarding the biological control of the Si cycle hinders accurate quantification. Only a concerted effort bringing scientists together from a broad array of disciplines will provide this new direction for research on vegetation-Si cycling.

Beer is a quintessential part of Belgian heritage. We performed a detailed analysis of factors controlling Si content in Belgian beers as a case study to coincide with the 2011 IBiS meeting in Antwerp (Belgium). Beer is one of the richest dietary sources of Si. Three decades of research have yielded evidence of a role for Si in human physiology: it plays an essential role in bone mineral density and reduces the biological availability of aluminium. We analysed 119 Belgian beers: highest dissolved Si concentrations were found in high fermentation, traditionally brewed ales. Concentrations ranged between 214 and 2,071 μmol L − 1. This is probably due to the complexity and length of the brewing procedure: longer, more complicated processing and presence of brewing sediment in the bottle allows more Si to dissolve out of the base products like hop, barley or even rice. As a side effect of fermentation, alcohol content was related to Si content.

Silica is well known for its role as inducible defence mechanism countering herbivore attack, mainly through precipitation of opaline, biogenic silica (BSi) bodies (phytoliths) in plant epidermal tissues. Even though grazing strongly interacts with other element cycles, its impact on terrestrial silica cycling has never been thoroughly considered. Here, BSi content of ingested grass, hay and faeces of large herbivores was quantified by performing multiple chemical extraction procedures for BSi, allowing the assessment of chemical reactivity. Dissolution experiments with grass and faeces were carried out to measure direct availability of BSi for dissolution. Average BSi and readily soluble silica numbers were higher in faeces as compared with grass or hay, and differences between herbivores could be related to distinct digestive strategies. Reactivity and dissolvability of BSi increases after digestion, mainly due to degradation of organic matrices, resulting in higher silica turnover rates and mobilization potential from terrestrial to aquatic ecosystems in non-grazed versus grazed pasture systems (2 versus 20 kg Si ha(-1) y(-1)). Our results suggest a crucial yet currently unexplored role of herbivores in determining silica export from land to ocean, where its availability is linked to eutrophication events and carbon sequestration through C-Si diatom interactions.

(1) University of Antwerp, Belgium, Department of Biology, Ecosystem Management Research Group, (2) Katholieke Universiteit Leuven, Belgium, Department of Earth and Environmental Sciences, (3) Catholic University of Louvain-la-Neuve, Belgium Department of Geology and Geography, (4) University of Antwerp, Belgium, StatUa Center for Statistics & Department of Environment, Technology and Technology management , (5) Erasmus University Rotterdam, Netherlands, Erasmus School of Economics, Departement of Business Economics

Continental export of Si to the coastal zone is closely linked to the ocean carbon sink and to the dynamics of phytoplankton blooms in coastal ecosystems. Presently, however, the impact of human cultivation of the landscape on terrestrial Si fluxes remains unquantified and is not incorporated in models for terrestrial Si mobilization. In this paper, we show that land use is the most important controlling factor of Si mobilization in temperate European watersheds, with sustained cultivation (>250 years) of formerly forested areas leading to a twofold to threefold decrease in baseflow delivery of Si. This is a breakthrough in our understanding of the biogeochemical Si cycle: it shows that human cultivation of the landscape should be recognized as an important controlling factor of terrestrial Si fluxes.

Amorphous, biogenic Si (ASi) is stored in large amounts in terrestrial ecosystems. The study of terrestrial ASi mobilization remains in the pioneer research stage: most Si budget studies have not included the biogenic amorphous Si stock and fluxes. This hampers our ability to accurately quantify terrestrial mobilization of Si, which is—through ocean carbon burial and CO 2 uptake during terrestrial Si weathering—intricately linked to global carbon budgets. We studied detailed concentration and load patterns of dissolved (DSi) and ASi during several high-discharge events in eight first-order river basins. Based on high frequency discharge measurements and concurrent analysis of ASi and DSi concentrations at base flow and during intense precipitation events, we were able to attribute a percentage of yearly ASi and DSi fluxes to both base flow and precipitation event related surface run-off. Our results show ASi and DSi concentrations in upstream river basins to be intricately linked to each other and to discharge, and ASi transport constitutes an important part to the total transport of Si even through first-order river basins (up to 40%). Based on our observations, increased occurrence of peak-discharge events with global climatic changes, and lowered importance of base flow, will coincide with drastic changes in ASi and DSi dynamics in the river continuum. Our work clearly shows ASi dynamics should be incorporated in global Si budgets now, even in low-order small river basins.

Silicon is one of the most important elements in the current age of the anthropocene. It has numerous industrial applications, and supports a high-tech multi-billion Euro industry. Silicon has a fascinating biological and geological cycle, interacting with other globally important biogeochemical cycles. In this review, we bring together both biological and geological aspects of the silicon cycle to provide a general, comprehensive review of the cycling of silicon in the environment. We hope this review will provide inspiration for researchers to study this fascinating element, as well as providing a background environmental context to those interested in silicon.