Phytoliths: Persistence & Release of Silicon in Soil and Plants – A Review

Phytoliths are formed from silica carried up from groundwater and some plants. The weathering of silicate minerals at the Earth’s surface provides large amounts of soluble silica, some of which is absorbed by growing plants. In solution, silica exists as mono silicic acid Si (OH4) with pH values of 2–9. It is carried upward in the vascular system and becomes concentrated during transpiration around the leaf stomata. The supersaturated solution begins to polymerize or gel then solidifies and forms solid opaline silica (SiO2:nH2O) bodies (phytoliths) within and between some of the plant cells. Phytoliths were extracted from the 7.4 meter loess core and analyzed morphologically and isotopically from the occluded carbon. Rates of isotopic fractionation between plant and phytolith were determined by measurements from many modern tree, fern, and grass species. The use of phytolith biochar as a Si fertilizer offers the undeniable potential to mitigate desilication and to enhance Si ecological services due to soil weathering and biomass removal. Silicon is accumulated at levels equal to or greater than essential nutrients in plant species belonging to the families Poaceae, Equisetaceae, and Cyperaceae. However, the abundance of silicon in soils is not an indication that sufficient supplies of soluble silicon are available for plant uptake.

Ancient Climate and Environmental History From Phytolith-Occluded Carbon

<p>The best records of atmospheric change of glacial cycles are those from ice cores. However, ice cores cannot provide estimates of changes in atmospheric 13CO2 because of as of yet unresolved technical problems. One of the least understood and important influences on the changes to the isotopic composition of atmospheric CO2 are that of vascular plants. While marine benthic delta 13C records have been used to infer past changes in terrestrial vegetation, accurate estimation of changes in carbon storage on land during ice ages has proved elusive. Other estimates have been made from terrestrial biomes of pollen records but a large discrepancy between marine and land based estimates remains. This thesis offers a new method of deriving an ancient atmospheric delta 13CO2 record using measurements of phytolith-occluded carbon as a proxy. The method is designed to measure delta 13CO2 in ancient phytolith-occluded carbon and convert this signal into an atmospheric delta 13CO2 estimate for the atmosphere. Phytoliths are very small particles of silica (between 5 and 100 microns) that form distinctive and repeatable shapes in most plants. When phytoliths form within a plant, some of the host organic matter is trapped inside the phytolith. Phytoliths have been shown to contain occluded carbon and are present in most terrestrial sedimentary deposits. Moreover, because they survive well in most soils and sediments, the trapped carbon remains intact and preserved from contamination and alteration. Experiments were conducted to characterise and measure the natural variability of modern phytolith-occluded carbon. These included measurement of carbon isotopic fractionation effects between the atmosphere and whole plant material, measurement of carbon isotope fractionation between whole plant matter and phytolith-occluded carbon, and a determination of carbon compounds present in phytolith-occluded carbon. A formula was developed for separating the plant physiological factors from the atmospheric 13CO2 value in the phytolith-occluded carbon, thus providing a basis for estimating atmospheric 13CO2 values. Phytoliths were extracted and occluded carbon analysed from a 7.4m loess core. Changes in phytolith assemblages were used to create a direct record of changes to the local vegetation cover, and isotopic analyses of carbon in phytoliths to generate a record of atmospheric 13CO2 for the last 120,000 years. The record exhibits a number of periods when the atmosphere had very low delta 13CO2 values that correspond with CH4 peaks in the Vostok ice core. It is hypothesized here that these low values are a consequence of the release of large volumes of methane released from marine hydrate (clathrate) deposits into the atmosphere, thereby, diluting atmospheric 13CO2.</p>

Ancient Climate and Environmental History From Phytolith-Occluded Carbon

<p>The best records of atmospheric change of glacial cycles are those from ice cores. However, ice cores cannot provide estimates of changes in atmospheric 13CO2 because of as of yet unresolved technical problems. One of the least understood and important influences on the changes to the isotopic composition of atmospheric CO2 are that of vascular plants. While marine benthic delta 13C records have been used to infer past changes in terrestrial vegetation, accurate estimation of changes in carbon storage on land during ice ages has proved elusive. Other estimates have been made from terrestrial biomes of pollen records but a large discrepancy between marine and land based estimates remains. This thesis offers a new method of deriving an ancient atmospheric delta 13CO2 record using measurements of phytolith-occluded carbon as a proxy. The method is designed to measure delta 13CO2 in ancient phytolith-occluded carbon and convert this signal into an atmospheric delta 13CO2 estimate for the atmosphere. Phytoliths are very small particles of silica (between 5 and 100 microns) that form distinctive and repeatable shapes in most plants. When phytoliths form within a plant, some of the host organic matter is trapped inside the phytolith. Phytoliths have been shown to contain occluded carbon and are present in most terrestrial sedimentary deposits. Moreover, because they survive well in most soils and sediments, the trapped carbon remains intact and preserved from contamination and alteration. Experiments were conducted to characterise and measure the natural variability of modern phytolith-occluded carbon. These included measurement of carbon isotopic fractionation effects between the atmosphere and whole plant material, measurement of carbon isotope fractionation between whole plant matter and phytolith-occluded carbon, and a determination of carbon compounds present in phytolith-occluded carbon. A formula was developed for separating the plant physiological factors from the atmospheric 13CO2 value in the phytolith-occluded carbon, thus providing a basis for estimating atmospheric 13CO2 values. Phytoliths were extracted and occluded carbon analysed from a 7.4m loess core. Changes in phytolith assemblages were used to create a direct record of changes to the local vegetation cover, and isotopic analyses of carbon in phytoliths to generate a record of atmospheric 13CO2 for the last 120,000 years. The record exhibits a number of periods when the atmosphere had very low delta 13CO2 values that correspond with CH4 peaks in the Vostok ice core. It is hypothesized here that these low values are a consequence of the release of large volumes of methane released from marine hydrate (clathrate) deposits into the atmosphere, thereby, diluting atmospheric 13CO2.</p>

Thermoplastic Intumescent Coatings Modified with Pentaerythritol-Occluded Carbon Nanotubes

A thermoplastic intumescent coating system (IC) based on poly(vinyl acetate) was modified by two forms of multiwalled carbon nanotubes (CNTs), i.e., by a nanofiller powder and its solid dispersions in pentaerythritol (PER-CNTs). It was revealed that only the PER-CNTs modifier allows us to obtain solvent-borne ICs with a relatively high CNTs concentration (1–3 wt. parts of CNTs/100 wt. parts of paint solids) and acceptable application viscosity. Thermal insulation time (TIT) and intumescent factor (IF) of the ICs on a steel substrate (a fire test according to a cellulosic fire curve), as well as morphology, chemical structure (by the FT-IR technique) and mechanical strength of the charred systems, were investigated. It was found that the CNTs powder decreases TIT and IF values while PER-occluded CNTs improve these parameters (e.g., +4.6 min and +102% vs. an unmodified sample, respectively). Compressive strength of the charred ICs was improved by the PER-CNTs modifier as well.

Drought influences the phytolith morphology variation and its occluded carbon of leaves in Dendrocalamus Ronganensis during growing season

&lt;p&gt;&lt;strong&gt;Abstract:&amp;#160;&lt;/strong&gt;Being an important carbon (C) sink on Earth, phytolith occluded carbon (PhytOC) has been investigated in various soil-plant systems. Yet, the environmental factor (i.e., drought) is less studied on the variation of phytolith, its relative depositions in plant tissues, morphology variations, and occluded carbon in the soil-plant systems. In this study, we analyzed the monthly variations of phytolith production and phytolith-occluded carbon (PhytOC) in the leaves of&lt;em&gt; Dendrocalamus ronganensis&lt;/em&gt; grown on a karst mountain in southwestern China. This study aimed to understand the drought factors influencing phytolith formation, morphology variation and carbon sequestration in plants. Our results showed that the phytolith assemblages and PhytOC between new and old leaves were significantly different, and varied with plant growth stages. The average PhytOC of old leaves and new leaves was 3.2% and 2.2%, respectively. In particular, both PhytOC and proportions of elongate, cuneiform and stomata phytolith in new leaves significantly decreased during drought months (from September to November).&lt;strong&gt; &lt;/strong&gt;This study suggests that PhytOC in plants is closely related to phytolith morphologies, and significantly affected by growth stage and hydrologic conditions of the growth environment. This indicates that we can improve the efficiency of phytolith carbon sequestration in plants and potentially reduce the atmospheric carbon dioxide content by improving the soil water conditions required for plant growth.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Keywords: &lt;/strong&gt;&lt;em&gt;Dendrocalamus ronganensis&lt;/em&gt;; phytolith; phytolith-occluded carbon; soil drought&lt;/p&gt;