The continental bio-cycling of silicon (Si) plays a key role in global Si cycle and as such partly controls global carbon (C) budget through nutrition of marine and terrestrial biota, accumulation of phytolith-occluded organic carbon (PhytOC) and weathering of silicate minerals. Despite the key role of elemental composition of phytoliths on their solubility in soils, the impact of plant cultivar and organ on the elemental composition of phytoliths in Si high-accumulator plants, such as rice (Oryza sativa) is not yet fully understood. Here we show that rice cultivar significantly impacts the elemental composition of phytoliths (Si, Al, Fe and C) in different organs of the shoot system (grains, sheath, leaf and stem). The amount of occluded OC within phytoliths is affected by contents of Si, Al and Fe in plants, while independent of the element composition of phytoliths. Our data document, for different cultivars, higher bio-available Si release from phytoliths of leaves and sheaths, which are characterized by higher enrichment with Al and Fe (i.e., lower Si/Al and Si/Fe ratios), compared to grains and stems. We indicate that phytolith solubility in soils may be controlled by rice cultivar and type of organs. Our results highlight that the role of the morphology, the hydration rate and the chemical composition in the solubility of phytoliths and the kinetic release of Si in soil solution needs to be studied further. This is central to a better understanding of the impact of soil amendment with different plant organs and cultivars on soil OC stock and on the delivery of dissolved Si as we show that sheath and leaf rice organs are both characterized by higher content of OC occluded in phytolith and higher phytolith solubility compared to grains and stems. Our study shows the importance of studying the impact of the agro-management on the evolution of sinks and sources of Si and C in soils used for Si-high accumulator plants.

/pdf/impact-of-rice-cultivar-and-organ-on-elemental-composition-4oez9nvtmp.pdf

Impact of rice cultivar and organ on elemental composition of phytoliths and the release of bio-available silicon.

https://cyberleninka.org/article/n/1302921.pdf

Plant biostimulants: Definition, concept, main categories and regulation

Positive ions that are available in soils absorb on grain surfaces. The total sum of cations that can be absorbed bij a soil/sediment at a certain PH is defined by the cation-exchange capacity (CEC, in meq g-1: mol equivalents per gram). The uptake of cations is an important parameter in agriculture and the larger the CEC, the more cations can be absorbed to the soil. The CEC depends highly on the pH of soil and sediments, where the CEC decreases with decreasing PH (increasing acidity). The exchange of ions on sediments occurs commonly fast on geological time scales, but the kinetics of adsorption in natural environments is still poorly understood. The strength of the bonding between the cations and the sediments varies from weak Van der Waals bondings (physical adsorption) to strong chemical bonds. The CEC is widely used for agricultural assessment because it is a measure of general soil fertility as well as an indicator of structural stability because CED is capabel of enhancing development of shrinkage cracks. The list below shows the CEC for different types of minerals. The data indicate that the CEC can vary over 2 orders of magnitude for various types of , minerals and can vary one order of magnitude within one soil type. Cation exchange capacity for different types of sediment (Eisma, 1992; Locher and de Bakker, 1990):

Cation exchange capacity.

Tree Rings And Climate

Impact of rice cultivar and organ on elemental composition of phytoliths and the release of bio-available silicon

. Silicon (Si) released as H4SiO4 by weathering of Si-containing solid phases is partly recycled through vegetation before its land-to-rivers transfer. By accumulating in terrestrial plants to a similar extent as some major macronutrients (0.1–10% Si dry weight), Si becomes largely mobile in the soil-plant system. Litter-fall leads to a substantial reactive biogenic silica pool in soil, which contributes to the release of dissolved Si (DSi) in soil solution. Understanding the biogeochemical cycle of silicon in surface environments and the DSi export from soils into rivers is crucial given that the marine primary bio-productivity depends on the availability of H4SiO4 for phytoplankton that requires Si. Continental fluxes of DSi seem to be deeply influenced by climate (temperature and runoff) as well as soil-vegetation systems. Therefore, continental areas can be characterized by various abilities to transfer DSi from soil-plant systems towards rivers. Here we pay special attention to those processes taking place in soil-plant systems and controlling the Si transfer towards rivers. We aim at identifying relevant geochemical tracers of Si pathways within the soil-plant system to obtain a better understanding of the origin of DSi exported towards rivers. In this review, we compare different soil-plant systems (weathering-unlimited and weathering-limited environments) and the variations of the geochemical tracers (Ge/Si ratios and δ30Si) in DSi outputs. We recommend the use of biogeochemical tracers in combination with Si mass-balances and detailed physico-chemical characterization of soil-plant systems to allow better insight in the sources and fate of Si in these biogeochemical systems.

/pdf/tracing-the-origin-of-dissolved-silicon-transferred-from-1zis5q5cky.pdf

Tracing the origin of dissolved silicon transferred from various soil-plant systems towards rivers: a review

The quantification of silicon (Si) uptake by tree species is a mandatory step to study the role of forest vegetations in the global cycle of Si. Forest tree species can impact the hydrological output of dissolved Si (DSi) through root induced weathering of silicates but also through Si uptake and restitution via litterfall. Here, monospecific stands of Douglas fir, Norway spruce, Black pine, European beech and oak established in identical soil and climate conditions were used to quantify Si uptake, immobilization and restitution. We measured the Si contents in various compartments of the soil–tree system and we further studied the impact of the recycling of Si by forest trees on the DSi pool. Si is mainly accumulated in leaves and needles in comparison with other tree compartments (branches, stembark and stemwood). The immobilization of Si in tree biomass represents less than 15% of the total Si uptake. Annual Si uptake by oak and European beech stands is 18.5 and 23.3 kg ha−1 year−1, respectively. Black pine has a very low annual Si uptake (2.3 kg ha−1 year−1) in comparison with Douglas fir (30.6 kg ha−1 year−1) and Norway spruce (43.5 kg ha−1 year−1). The recycling of Si by forest trees plays a major role in the continental Si cycle since tree species greatly influence the uptake and restitution of Si. Moreover, we remark that the annual tree uptake is negatively correlated with the annual DSi output at 60 cm depth. The land–ocean fluxes of DSi are certainly influenced by geochemical processes such as weathering of primary minerals and formation of secondary minerals but also by biological processes such as root uptake.

Tree species impact the terrestrial cycle of silicon through various uptakes

Summary
Soil is the primary source of plant silicon (Si) and therefore a key reservoir of the Si biological cycling. Soil processes control the stock of Si-bearing minerals and the release of dissolved Si (DSi), hence the Si fluxes at the Earth's surface. Here, we review the interdependent relationship between soil processes and the return of plant Si in soils, and their controls on the biological Si feedback loop.
Dissolution and precipitation of soil silicate minerals govern the bioavailability of Si. Plants affect Si biocycling through mineral weathering, root uptake, phytolith formation, return and dissolution in soil. Thus, soil processes and Si biocycling readily interact in soil–plant systems.
Rock mineral weathering and soil formation are driven by the five soil-forming factors: parent rock, climate, topography, age and biota. These factors govern Si fluxes in soil–plant systems since they impact both the mineral weathering rate and fate of DSi. The variability of soil-forming factors at a global scale explains both the soil diversity and high variability of the rates of Si cycling in terrestrial ecosystems.
Plants play a crucial role in soil evolution by promoting weathering and forming phytoliths (plant silica bodies). They thus act as Si sinks and sources. With increasing depletion of lithogenic (LSi) and pedogenic (PSi) silicates, the biological Si feedback loop progressively takes over the Si plant uptake from weatherable LSi and PSi minerals. With rising weathering, the soil becomes increasingly concentrated in phytoliths, phytogenic amorphous silicates (PhSi), which are constantly formed in plant and dissolved in soil. Paradoxically, the Si biocycling is thus more intense in soils depleted in primary LSi source. By converting soil LSi and PSi into PhSi, plants increase the mobility of Si in soil and alleviate desilication in the topsoil. Non-essential plant Si is therefore an essential link between mineral and living worlds.
The dynamics of Si in terrestrial ecosystems is thus largely governed by pedogenesis and its relationship with plant community and diversity. Consequently, the appraisal of soil constituents and processes is central to further understand their interaction with the biological Si feedback loop.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/1365-2435.12704

Jean-Thomas Cornélis

Papers

Impact of rice cultivar and organ on elemental composition of phytoliths and the release of bio-available silicon.

Impact of rice cultivar and organ on elemental composition of phytoliths and the release of bio-available silicon

Tracing the origin of dissolved silicon transferred from various soil-plant systems towards rivers: a review

Tree species impact the terrestrial cycle of silicon through various uptakes

Soil processes drive the biological silicon feedback loop