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

Author(s):  
A. Senthilkumar ◽  
B. Bhakiyathu Saliha ◽  
P. Saravana Pandian ◽  
R. Thamizh Vendan ◽  
A. Gurusamy ◽  
...  

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.

Hacquetia ◽  
2018 ◽  
Vol 17 (1) ◽  
pp. 5-16 ◽  
Author(s):  
Orsolya Valkó ◽  
Stephen Venn ◽  
Michał Żmihorski ◽  
Idoia Biurrun ◽  
Rocco Labadessa ◽  
...  

Abstract Disturbance by biomass removal is a crucial mechanism maintaining the diversity of Palaearctic grasslands, which are unique biodiversity hotspots. The century-long traditional land use of mowing, grazing and burning, has been fundamentally changed in many parts of the Palaearctic. Due to socio-economic changes, large areas of former pastures and meadows have been abandoned, leading to a succession towards secondary scrublands or forest and the encroachment of competitor grass species, all leading to a decrease in biodiversity. Here we report the causes and consequences of the cessation of traditional grassland management regimes, provide strategies for reducing the impact of abandonment and consider these from the perspective of sustainability. We consider the possibilities for initiating sustainable management regimes in the contemporary socio-economic environment, and discuss the prospects and limitation of alternative management regimes in the conservation of grassland biodiversity. These themes are also the core topics of this Special Feature, edited by the EDGG. We hope that this Special Feature will encourage steps towards more sustainable strategies for the conservation of Palaearctic grasslands and the integration of the sustainability perspective into their conservation.


2009 ◽  
Vol 73 (24) ◽  
pp. 7226-7240 ◽  
Author(s):  
S. Opfergelt ◽  
G. de Bournonville ◽  
D. Cardinal ◽  
L. André ◽  
S. Delstanche ◽  
...  

2011 ◽  
Vol 7 (2) ◽  
pp. 887-920 ◽  
Author(s):  
J. Xiao ◽  
Y. K. Xiao ◽  
C. Q. Liu ◽  
Z. D. Jin

Abstract. Experiments involving boron incorporation into brucite (Mg(OH)2) from magnesium-free artificial seawater with pH values ranging from 9.5 to 13.0 were carried out to better understand the incorporation behavior of boron into brucite. The results show that both concentration of boron in deposited brucite ([B]d) and its boron partition coefficient (Kd) between deposited brucite and final seawater are controlled by pH of the solution. The incorporation capacity of boron into brucite is much stronger than that into oxides and clay minerals. The isotopic compositions of boron in deposited brucite (δ11Bd) are higher than those in the associated artificial seawater (δ11Bisw) with fractionation factors ranging between 1.0177 and 1.0569, resulting from the preferential incorporation of B(OH)3 into brucite. Both boron adsorptions onto brucite and precipitation reaction of H3BO3 with brucite exist during deposition of brucite from artificial seawater. The simultaneous occurrence of both processes determines the boron concentration and isotopic fractionation of brucite. The isotopic fractionation behaviors and mechanisms of boron incorporated into brucite are different from those into carbonates. Furthermore, the isotopic compositions of boron in modern corals might be affected by the existence of brucite in madrepore and the preferential incorporation of B(OH)3 into brucite. An exploratory study for the influence of brucite on the boron isotopic composition in modern corals is justifiable.


2002 ◽  
Vol 757 ◽  
Author(s):  
Taiji Chida ◽  
Yuichi Niibori ◽  
Osamu Tochiyama ◽  
Koichi Tanaka

ABSTRACTSince silica undergoes polymerization, precipitation, and dissolution depending on the change in pH or temperature, the chemical behavior of silica would be much complicated when cement for the construction of geological disposal system greatly changes the pH (8 to 13) of groundwater. To clarify the dynamic behavior of silica in such an alkaline solution, the concentrations of silica in both soluble and colloidal form in the supersaturated solution in the presence of solid phase have been traced over a 40-day period. In the experiment, the concentration of silica in a soluble form was determined by the silicomolybdenum-yellow method, and the concentration of silica in soluble plus colloidal forms was determined by adjusting the pH of the solution to 13, where all the silica changes into a soluble form (mainly monomeric). In order to examine the dynamic behavior of colloidal silica with solid phase of silica, this study has used natural quartz and pure commercial amorphous silica, both in a size fraction of 74–149 μm, whose specific surface-area (BET, N2 gas) were respectively 1.0 m2/g and 400 m2/g. The Na2SiO3 solution (250 ml, pH>10, 298 K) was poured into a polyethylene vessel containing quartz or amorphous silica (0.1 g or 0.5 g), HNO3 and a buffer solution. The pH of the solution was set to 8. The silica initially in a soluble form at pH>10 (6.8×10-3 M or 1.2×10-2 M) became supersaturated and either deposited on the solid surface or changed into the colloidal form. The ratio of silica in those form depended both on the initial concentration of soluble-silica and the surface area of the solid. The concentration of colloidal-silica gradually decreased, where the logarithm of its concentration decreased linearly against time after the concentration of soluble-silica decreased to a metastable concentration slightly higher than the solubility of soluble-silica.


2021 ◽  
Author(s):  
◽  
John Alec Carter

<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>


2011 ◽  
Vol 7 (3) ◽  
pp. 693-706 ◽  
Author(s):  
J. Xiao ◽  
Y. K. Xiao ◽  
C. Q. Liu ◽  
Z. D. Jin

Abstract. Experiments involving boron incorporation into brucite (Mg(OH)2) from magnesium-free artificial seawater with pH values ranging from 9.5 to 13.0 were carried out to better understand the incorporation behavior of boron into brucite and the influence of it on Mg/Ca-SST proxy and δ11B-pH proxy. The results show that both the concentration of boron in deposited brucite ([B]d) and its boron partition coefficient (Kd) between deposited brucite and final seawater are controlled by the pH of the solution. The incorporation capacity of boron into brucite is almost the same as that into corals, but much stronger than that into oxides and clay minerals. The isotopic compositions of boron in deposited brucite (δ11Bd) are higher than those in the associated artificial seawater (δ11Bisw) with fractionation factors ranging between 1.0177 and 1.0569, resulting from the preferential incorporation of B(OH)3 into brucite. Both boron adsorptions onto brucite and the precipitation reaction of H3BO3 with brucite exist during deposition of brucite from artificial seawater. The simultaneous occurrence of both processes determines the boron concentration and isotopic fractionation of brucite. The isotopic fractionation behaviors and mechanisms of boron incorporated into brucite are different from those into corals. The existence of brucite in corals can affect the δ11B and Mg/Ca in corals and influences the Mg/Ca-SST proxy and δ11B-pH proxy negatively. The relationship between δ11B and Mg/Ca in corals can be used to judge the existence of brucite in corals, which should provide a reliable method for better use of δ11B and Mg/Ca in corals to reconstruct paleo-marine environment.


Soil Research ◽  
1964 ◽  
Vol 2 (1) ◽  
pp. 33 ◽  
Author(s):  
RS Beckwith ◽  
R Reeve

The release of monosilicic acid into solution from soils has been studied under near-neutral and acid conditions. For all soils examined the final concentration of silica decreased with decreasing soil : solution ratio but larger total amounts were released into the larger volumes of extractant. The amount of silica extracted from any one soil varied with pH in a manner similar to that reported previously for residual amounts of monosilicic acid added to soil suspensions, viz. release was minimal at pH 7-9 and increased continuously with acidity. Citrate ions promoted release of native silica from soils as well as partially preventing sorption of added monosilicic acid. The inference of Part I, that much readily soluble silica may be derived from sorption sites in soils, has thus received additional confirmation. Studies have also been made of the release of silica both from some clay minerals and from synthetic sesquioxides on which monosilicic acid was previously sorbed. The release of sorbed monosilicic acid from sesquioxides resembles release from soils in its dependence on pH; iron and aluminium oxides are considered to be responsible for most of the retention of monosilicic acid by soils. Much of the silica rapidly dissolved from soils by N hydrochloric acid is also believed to be derived from sorption sites, and the use of an acid extractant for assessing the 'reactive silica' status of soils is briefly discussed. Suspensions of fine quartz or amorphous silica were partly converted to sorbed silicic acid in the presence of sesquioxides, and it appears that finely divided silica, even quartz, is not stable at near-neutral pH values in the presence of excess sesquioxides. The results of the investigations have been discussed briefly in relation to the availability of soil phosphate and the amounts of sorbed silicic acids occurring in various soils.


2021 ◽  
Author(s):  
◽  
John Alec Carter

<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>


Author(s):  
A. E. Hotchkiss ◽  
A. T. Hotchkiss ◽  
R. P. Apkarian

Multicellular green algae may be an ancestral form of the vascular plants. These algae exhibit cell wall structure, chlorophyll pigmentation, and physiological processes similar to those of higher plants. The presence of a vascular system which provides water, minerals, and nutrients to remote tissues in higher plants was believed unnecessary for the algae. Among the green algae, the Chaetophorales are complex highly branched forms that might require some means of nutrient transport. The Chaetophorales do possess apical meristematic groups of cells that have growth orientations suggestive of stem and root positions. Branches of Chaetophora incressata were examined by the scanning electron microscope (SEM) for ultrastructural evidence of pro-vascular transport.


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