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Silicon in the critical zone under global change: towards an integrated view from ecological, agronomical, paleo and geochemical perspectives

Silicon (Si) is crucial in numerous biochemical and geochemical processes. Earlier scientific literature on Si cycling focused on abiotic weathering processes, while in recent years, scientists have become more aware of the significant role of biotic controls. Silicon plays a key role in processes governing soil formation and soil-plant feedback interactions. Vegetation, soil organisms, including fauna, microorganisms and fungi, strongly affect Si dynamic in terrestrial ecosystems but the mechanisms are still poorly understood. In particular, Si has numerous beneficial effects on both plant structure, function as well as resilience to biotic and abiotic stresses motivating studies focusing on Si functional ecology and silica biomineralization. The global Si cycle is receiving increased attention because of its links with the carbon cycle as well as other major biogeochemical cycles and toxic elements. A better understanding of the terrestrial Si cycle is thus critical, especially as drastic and subtle changes in the terrestrial Si cycle are occurring worldwide in response to global change.
This session aims at compiling recent work focusing on biogeochemical Si cycling under global change, its functions in terrestrial ecosystems as well as its evolution in the recent past. This session bridges advances from soil sciences, ecology, plant physiology, agronomy, biogeochemistry (including isotopes studies) and palaeontology. We invite studies tackling biotic and abiotic interactions at different time and spatial scales affecting the Si cycle and its interactions with other biogeochemical cycles. We encourage interdisciplinary studies as well as contributions from both field and laboratory experiments encompassing biogeochemical processes, molecular mechanisms to improve our understanding of the role of Si in ecosystem processes. Meta-analyses and paleo-environmental studies using phytoliths are also welcome.

Co-organized by SSS8
Convener: Julia Cooke | Co-conveners: Rivka Elbaum, Scott Johnson, Zimin LiECSECS, Joerg Schaller
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Wed, 28 Apr, 09:00–10:30

Chairpersons: Zimin Li, Scott Johnson, Rivka Elbaum

5-minute convener introduction

Ofir Katz

Plant Si plays considerable roles in plant, animal. Ecosystem and global ecologies, including biogeochemical cycles. Understanding the ecological roles of plant Si and their evolutionary history is fundamental for increasing our understanding of this phenomenon, its origins, and its significance for past, present and future ecosystems. For these reasons, plant Si research is becoming increasingly interdisciplinary and superdisciplinary. Nevertheless, understanding the evolution of this phenomenon and its interactions with biogeochemical cycles – and furthermore understanding the implications for current and prospected environmental change – is hindered by inappropriate consideration of chronology and community ecology.

studies of the evolution of plant Si uptake, its ecology and its effects on ecosystem functioning suggest multiple types of Si-C interactions. These include – for example – Si-C tradeoffs within plants, a role of Si uptake and cycling in the C cycle (mostly C sequestration through NPP, weathering and occlusion), and Si mediating plant responses to CO2 changes. While these suggest that plant Si may have evolved partially in response to changing CO2 concentrations throughout the Cainozoic, implied by the contemporaneous spread of Si-rich grasslands when CO2 levels drop. However, recent paleontological and molecular suggest no temporal match. Likewise, the possibility of Si-rich grasses and abrasion-adapted grazers is also challenged by evidence for Si having an antiherbivory role on the one hand, and lack of chronological matches on the other hand. These discrepancies may stem, in part, from two considerations that may often be overlooked, about chronology, ecology and how they connect.

First, species and their traits, as well as whole ecosystems, should be seen in the context of their entire evolutionary history, and may therefore reflect not only adaptations to extant selective forces but be anachronisms. Moreover, evolutionary history and evolutionary transitions are complex, resulting in true and apparent asynchronisms. Second, evolution and ecology are multi-scalar, in which various phenomena and processes act at various scales. In ecology, there can be great differences between how a single species responds (e.g., in monoculture) and how different responses of different species interact to shape communities, and further how changes in communities interact with other ecosystem components to shape ecosystems.

Consequently, our understanding of how plant Si may have evolved in response to CO2 and herbivory, and how it may affect ecosystem functions such as biogeochemical cycling under current environmental changes, requires further thinking.

How to cite: Katz, O.: It is time to interact: chronology and ecology in studying plant Si, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7064, https://doi.org/10.5194/egusphere-egu21-7064, 2021.

Chengpeng Huang et al.

The use of exogenous silicon (Si) amendments, such as Si fertilizers and biochar, can effectively increase crop Si uptake and the formation of phytoliths, which are siliceous substances that are abundant in numerous plant species. Phytolith-occluded carbon (C) (PhytOC) accumulation in soil plays an important role in long-term soil organic C (SOC) storage. Nevertheless, the effects of both Si fertilizer and biochar application on PhytOC sequestration in forest plant-soil systems have not been studied. We investigated the impact of Si fertilizer and biochar applications on 1) the PhytOC pool size, the solubility of plant and soil phytoliths, and soil PhytOC in soil physical fractions (light (LFOM) and heavy fractions of organic matter (HFOM)) in Moso bamboo (Phyllostachys pubescens) forests; and 2) the relationships among plant and soil PhytOC concentrations and soil properties. We used a factorial design with three Si fertilizer application rates: 0 (S0), 225 (S1) and 450 (S2) kg Si ha−1, and two biochar application rates: 0 (B0) and 10 (B1) t ha−1. The concentrations of PhytOC in the bamboo plants and topsoil (0–10 cm) increased with increasing Si fertilizer addition, regardless of biochar application. Biochar addition increased the soil PhytOC pool size, as well as the LFOM- and HFOM-PhytOC fractions, regardless of Si fertilizer application. The Si fertilizer application increased or had no effect on soil phytolith solubility with or without biochar application, respectively. Soil PhytOC was correlated with the concentration of soil organic nitrogen (R2=0.32), SOC (R2=0.51), pH (R2=0.28), and available Si (R2=0.23). Furthermore, Si fertilizer application increased plant and soil PhytOC by increasing soil available Si. Moreover, biochar application increased soil PhytOC concentration in LFOM-PhytOC and the unstable fraction of PhytOC. We conclude that Si fertilizer and biochar application promoted PhytOC sequestration in the plant-soil system and changed its distribution in physical fractions in the Moso bamboo plantation in subtropical China.

How to cite: Huang, C., Wang, L., Gong, X., Huang, Z., Zhou, M., Li, J., Wu, J., Chang, S. X., and Jiang, P.: Silicon fertilizer and biochar effects on plant and soil PhytOC concentration and soil PhytOC stability and fractionation in subtropical bamboo plantations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1876, https://doi.org/10.5194/egusphere-egu21-1876, 2021.

Daniel Puppe

Biogenic silicon (BSi) has been found to play a fundamental role in the link between global Si and carbon cycles, because it represents a key factor in the control of Si fluxes from terrestrial to aquatic ecosystems. Furthermore, various beneficial effects of Si accumulation in plants have been revealed, i.e., increased resistance against abiotic and biotic stresses. Thus Si is of great importance for agricultural plant-soil systems. Due to intensified land use humans directly influence Si cycling on a global scale. For example, Si exports through harvested crops and increased erosion rates generally lead to a Si loss in agricultural systems with implications for Si bioavailability in agricultural soils, which is controlled by BSi to a great extent. However, while corresponding research on phytogenic BSi (i.e., BSi synthesized by plants) has been established for decades now, studies dealing with protozoic BSi (i.e., BSi synthesized by testate amoebae) have been conducted just recently. By reviewing these studies I found them to indicate that testate amoebae might play a key role in Si cycling in terrestrial ecosystems. Actually, annual biosilicification rates of idiosomic testate amoebae are comparable to or even exceed annual Si uptake rates of trees. Furthermore, it is most likely that total protozoic Si pools (considering not only intact shells but also single idiosomes, the building blocks of testate amoeba shells) are much bigger than given in publications yet, because it can be assumed that idiosomes most likely can be as stable as phytoliths (representing the phytogenic Si pool in soils), and thus are well preserved in soils. Consequently, it would be not surprising if total protozoic Si pool quantities (shells plus single idiosomes) would be found to equal phytogenic Si pool quantities in soils. With my contribution I would like to encourage further field and laboratory research to verify this assumption and gain a deeper understanding of Si cycling by testate amoebae in terrestrial ecosystems.

How to cite: Puppe, D.: It is not plants alone – Protozoic silica and its role in terrestrial silicon cycling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2679, https://doi.org/10.5194/egusphere-egu21-2679, 2021.

Félix de Tombeur et al.

Silicon (Si) is widely recognized as an important regulator of the global carbon (C) cycle via its effect on diatom productivity in oceans and the weathering of silicate minerals on continents. Si is also a beneficial plant nutrient, improving resistance to herbivory and pathogens and mitigating the negative effects of several abiotic stresses, including nutrient limitation. However, changes in Si sources and cycling during long-term development of terrestrial ecosystems remain poorly understood. We studied Si in soils and plants along two 2-Ma coastal dune chronosequences in southwestern Australia (Jurien Bay and Guilderton). Soil development along these chronosequences includes carbonate leaching in Holocene soils, formation of secondary Si-bearing minerals in Mid-Pleistocene soils, followed by their loss via dissolution, to yield quartz-rich soils of Early-Pleistocene age. The chronosequences also exhibit an extreme gradient of soil fertility in terms of rock-derived nutrients, and shifts from nitrogen (N) to phosphorus (P) limitation of plant productivity as soils age. Along each chronosequence, we quantified the pools of reactive Si-bearing phases and plant-available Si in the soils, and physically extracted soil phytoliths (amorphous silica formed in plant tissues). We also quantified Si, macronutrients and total phenols in the most abundant plants growing along the best-studied of the two chronosequences (Jurien Bay). We found that plant-available Si was lowest in young and carbonate-rich soils, because carbonates weathering reduces the weathering of silicate minerals by consuming protons, and Si is strongly sorbed by secondary minerals in alkaline soils. Plant-available Si increased in intermediate-age soils during the formation of secondary minerals (kaolinite), and finally decreased in old, quartz-rich soils, due to continuous desilication. As pedogenic Si pools became depleted with increasing soil age, Si availability was increasingly determined by soil phytoliths. At Jurien Bay, foliar Si increased continuously as soils aged, in contrast with foliar macronutrients that declined markedly in strongly weathered soils. Finally, foliar phenol concentrations declined with increasing soil age and were negatively correlated with foliar Si at the community and individual species level, suggesting a tradeoff between these two leaf defense strategies. Our results highlight a nonlinear response of plant-available Si to long-term pedogenesis, with an increase during carbonate loss and a decrease in the silicates weathering domain. They also demonstrate that the retention of Si by plants during ecosystem retrogression sustains its terrestrial cycling by leveraging the high reactivity of soil phytoliths compared with soil-derived aluminosilicates. Moreover, the continuous increase of plant Si concentrations as rock-derived nutrients are depleted suggests important plant benefits associated with Si in P-impoverished environments. This is in line with the resource availability hypothesis, which predicts that plants adapted to infertile soils have high levels of anti-herbivore leaf defenses. In particular, old and P-depleted soils increased the relative expression of Si-based defenses, while young soils where plant productivity is limited by N promoted leaf phenol accumulation. Overall, our results demonstrate that long-term ecosystem and soil development strongly influence soil-plant Si dynamics, with cascading effects on plant ecology and global Si and C biogeochemistry.

How to cite: de Tombeur, F., Turner, B., Laliberté, E., Lambers, H., Mahy, G., Faucon, M.-P., Zemunik, G., and Cornélis, J.-T.: Long-term silicon dynamics in terrestrial ecosystems: insights from 2-million years soil chronosequences, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1105, https://doi.org/10.5194/egusphere-egu21-1105, 2021.

Zhaoliang Song and Yuntao Wu

Phytoliths in most terrestrial plant tissues as a result of silica biomineralization may occlude 0.1–6% of organic carbon (C). Phytolith-occluded carbon (PhytOC) comes mainly from photosynthesis and can be stable in soil and sediment environments for several hundred to thousand years. Phytolith turnover may influence terrestrial biogeochemical C cycle either directly through phytolith C sequestration or indirectly through regulating plant biomass C composition and accumulation, and soil organic carbon (SOC) stability. Phytolith C sequestration rates in terrestrial ecosystems of China increase in the following order: grasslands < forests < croplands. Active management practices including cultivation of silicon (Si)-rich plants and amendment of Si-rich materials (e.g., basalt powder and biochar) to increase aboveground net primary productivity (ANPP) and Si supply can significantly increase phytolith C sequestration. The dissolved Si from silicate weathering and phytolith dissolution can decrease plant lignin content and increase the accumulation of plant biomass C through mitigating abiotic and biotic stresses and improving stoichiometry of C, nitrogen (N) and phosphorus (P). The recovery of plant biomass C in response to Si accumulation usually exhibits an S-shaped curve under biotic stress and a bell-shaped curve under abiotic stresses. Generally, Si can recover approximately 30 to 40% of plant biomass C under abiotic and biotic stresses. Phytolith and related dissolved Si in soils can increase SOC stability through phytolith adsorption, Si and aluminum interaction, and Si and iron interaction.

How to cite: Song, Z. and Wu, Y.: Phytolith biogeochemistry and silicon regulation of terrestrial biogeochemical carbon cycle, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2004, https://doi.org/10.5194/egusphere-egu21-2004, 2021.

Lin Xu et al.

Forest ecosystem has a high carbon sequestration capacity and plays a crucial role in maintaining global carbon balance and climate change. Phytolith-occluded carbon (PhytOC), a promising long-term biogeochemical carbon sequestration mechanism, has attracted more attentions in the global carbon cycle and the regulation of atmospheric CO2. Therefore, it is of practical significance to investigate the PhytOC accumulation in forest ecosystems. Previous studies have mostly focused on the estimation of the content and storage of PhytOC, while there were still few studies on how the management practices affect the PhytOC content. Here, this study focused on the effects of four management practices (compound fertilization, silicon fertilization, cut and control) on the increase of phytolith and PhytOC in Moso bamboo forests. We found that silicon fertilization had a greater potential to significantly promote the capacity of carbon sequestration in Moso bamboo forests. this finding positively corresponds recent studies that the application of silicon fertilizers (e.g., biochar) increase the Si uptake1 to promote phytolith accumulation and its PhytOC sequestration in the plant-soil system2. Of course, the above-mentioned document2 also had their own shortcomings, i.e., the experimental research time was not long, lacking long-term follow-up trial and the bamboo forest parts were also limited, so that the test results lack certain reliability. We have set up a long-term experiment plot to study the effects of silicon fertilizer on the formation and stability of phytolith and PhytOC in Moso bamboo forests. But anyway, different forest management practices, especially the application of high-efficiency silicon-rich fertilizers1, may be an effective way to increase the phytolith and PhytOC storage in forest ecosystems, and thereby improve the long-term CO2 sequestration capacity of forest ecosystems. Research in this study provides a good "forest plan" to achieve their national voluntary emission reduction commitments and achieves carbon neutrality goals for all over the world.


1Li et al., 2019. Plant and soil, 438(1-2), pp.187-203.

2Huang et al., 2020, Science of The Total Environment, 715, p.136846.

How to cite: Xu, L., Shi, Y., Lv, W., Niu, Z., Yuan, N., and Zhou, Y.: Effect of forest management on the formation and stability of phytolith and PhytOC in forest ecosystem, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-573, https://doi.org/10.5194/egusphere-egu21-573, 2021.

Vidusanka Thilakanayaka et al.

Silicon is important as a nutrient for phytoplankton (diatom, radiolarian, silicoflagellates and sponges) and for the phytolith production by terrestrial vegetation. Silicon also contributes in removing carbon dioxide from the atmosphere through silicate weathering.  Hence it is important to understand the behavior of the silicon cycle throughout earth history. Silica is the second most abundant element in the earth's crust and the concentration of silicic acid in the marine environment has not changed since the past 10,000 years. Phytolith plays an important role in the silicon cycle. While the phytoplankton in marine environment bioengineers silica within the water column, phytolith transports terrestrial biogenic silica into the marine environment and act as a silicon sink. Though astonishingly, very few researches have been carried out in the field of marine phytolith sink and also on the phytoliths in the marine environment.

For this study, we have chosen the world highest terrestrial sediment receiving submarine fan, the Bengal fan. The core sample was extracted at a water depth of 3520m at 85.960985 N, 9.99351 E. 24 phytolith types were identified and all the morphotypes were counted dividing into three size classes. These size classes were specific to considering morphotypes. Most related simple geometries were used to calculate the volume of phytolith cells and these volume data were used in calculating the total volume of phytolith in one gram of sediment by combining with an absolute abundance of phytolith data for each size class, which were later used to calculate the total weight of phytolith in one gram of marine sediment. According to the results in deep oceanic sediment at the core, the location contains ⁓0.15mg/g phytolith during the low phytolith flux periods (ex. Late Holocene) and ⁓2.678mg/g of phytolith during the high phytolith flux periods such as 25ka to 30ka B.P. and around the beginning of deglaciation. After removing 10% from the total weight as phytolith occluded carbon (PhytOC), phytolith derived biogenic silica content in sediment varies from ⁓0.135mg/g - ⁓2.41mg/g. Thus, phytolith in marine sediment contributes as a permanent silicon and carbon sink. By considering average marine sediment density as 1.7g/cm3, in a 1cm thick, one square km sediment layer contains ⁓2 to 40 metric tons of biogenic silica derived from phytolith, during low and high phytolith flux periods. This study serves as the pioneer of this field of study and further it is important to investigate the release of biogenic silica in to marine environment by phytolith and PhytOC content in different morphotypes and in different geological regions, for better understanding the contribution of phytolith to the biogenic silicon cycle in the marine environment.

Keywords: Marine phytolith, Deep oceanic sediment, Silicon cycle, Phytolith Flux, Silicon sink.


This work was funded by the National Natural Science Foundation of China (NSFC 41876062) and Key Special Project for Introduced Talents Team of Southern Marine Science and EngineeringGuangdong Laboratory (Guangzhou) (GML2019ZD0206).


How to cite: Thilakanayaka, V., Chuanxiu*, L., and Xiang, R.: Contribution of terrestrially derived phytolith as a marine silicon sink, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3989, https://doi.org/10.5194/egusphere-egu21-3989, 2021.

Fikadu Biru et al.

Silicon (Si) has important role in mitigating diverse biotic and abiotic stresses, mainly via silicification of plant tissues. However, environmental changes such as reduced atmospheric CO2 concentrations may affect grass Si concentration which, in turn, can alter herbivore performance. Recently, we demonstrated that pre-industrial atmospheric CO2 increased Si accumulation in a grass, however, how Si is deposited and whether this affects insect herbivores performance is unknown. We, therefore, investigated how pre-industrial (reduced) (rCO2, 200 ppm), ambient (aCO2, 410 ppm) and elevated (eCO2, 640 ppm) CO2 concentrations and Si-treatments (Si+ or Si-) affect Si accumulation in the model grass, Brachypodium distachyon and its subsequent effects on the performance of the global insect, Helicoverpa armigera. rCO2 caused Si concentrations to increase by 29% and 36% compared to aCO2 and eCO2, respectively. Furthermore, increased Si accumulation under rCO2 decreased herbivore relative growth rate (RGR) by 120% relative to eCO2, whereas rCO2 caused herbivore RGR to decrease by 26% compared to eCO2. Moreover, Si supplementation increased the density of trichomes, silica and prickle cells, and these changes in leaf surface morphology reduced larval feeding performance. The observed negative correlation between macrohair density, silica cell density, prickle cell density and herbivore RGR supports this. To our knowledge, this is the first study to demonstrate that increased Si accumulation under pre-industrial CO2 environment reduced the performance of this generalist insect herbivore performance. Contrastingly, we found  reduced Si accumulation under higher CO2, which suggests  that some grasses might become more susceptible to insect herbivore under the projected climate change scenarios.

How to cite: Biru, F., Islam, T., Cibils-Steward, X., Cazzonelli, C., Elbaum, R., and Johnson, S.: Anti-herbivore silicon defences in a model grass are greatest under Miocene levels of atmospheric CO2, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9709, https://doi.org/10.5194/egusphere-egu21-9709, 2021.

Julia Cooke

Estimates of silicon (Si) pools and fluxes in diverse extant ecosystems have been published, including for grasslands, and deciduous and evergreen forests.  These illustrate diversity in dominant pools of biogenic Si in soils versus living biomass, reflecting the vegetation type and variation in Si accumulation of plant groups. This presentation will explore potential to estimate Si pools and fluxes for a selection of past environments, based on the species recorded in fossil records teamed with Si accumulation data from extant relatives. Where possible, changes over time will also be considered incluing impacts of vegetation on weathering and other envrionmental feedbacks.

How to cite: Cooke, J.: Terrestrial ecosystem Si budgets, past and present, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16003, https://doi.org/10.5194/egusphere-egu21-16003, 2021.

Camille Delvigne et al.

One of the most puzzling properties of silicon (Si) is its differential absorption by plants. Depending on the plant species, water and soil Si availability, environmental factors such as grazing and temperature, plant Si contents can vary from 0.1 % to 10 %(on a dry weight basis). Advances in genomics improved our understanding of biochemical and molecular mechanisms underlying plant Si uptake providing a framework to explain the variability of Si in plants and its distribution. Yet complex Si roles in plant strategies, its dependence on environmental factors and in mediating interactions with their environments and other organisms remain misunderstood. How is plant Si uptake affected by soil Si availability and how is Si distribution between tissue types controlled? It is hard for us to answer those questions even if Si plant traits are an indicator of the soil Si status. For example, a few studies showed that Si content and phytolith distribution are mainly controlled by Si availability. In this study, a pot experiment was conducted in a greenhouse where wheat (Triticum turgidum L.) was grown on three different soils: an aric podzol, an andosol and a calcosol. These soils are contrasted in term of clay size distribution, SiO2 concentrations and organic matter content and are presumed to reflect French soils variability in term of Si dynamics. Here, we focus on how plant Si patterns, both Si content and Si isotopes, are linked to soil Si availability leading to new insights to the mechanisms underlying the different Si uptake and translocation strategies. This work is supported by the BIOSiSOL project (ANR-14-CE01-0002).

How to cite: Delvigne, C., Keller, C., Guihou, A., Basile-Doelsch, I., Angeletti, B., Deschamps, P., and Meunier, J.-D.: Silicon isotopes: linking soil Si availability and plant Si strategies, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12083, https://doi.org/10.5194/egusphere-egu21-12083, 2021.

Jamie Waterman et al.

1) Crop loss due to insect herbivory is one of the largest challenges facing the agricultural industry. As herbivore populations continue to grow in light of global change, securing crop resources is becoming increasingly critical. Silicon (Si) has been shown to effectively mitigate the adverse effects of herbivores such as the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae), in crop species (namely grasses), that have evolved the ability to uptake large amounts of Si through their roots and accumulate it in aboveground tissues. Nevertheless, the effectiveness of Si accumulation as a plant defence against herbivory in the short term, and its consequential effects on alternative defence responses, remain unclear.
2) We conducted two discrete experiments to determine the short-term dynamics of Si, chemical defences and resistance to herbivory in the model grass, Brachypodium distachyon: 1) Both Si-supplemented (+Si) and control (-Si) plants were treated with methyl jasmonate (MeJA) as a form of simulated herbivory and we measured the interplay of Si accumulation, the phytohormones jasmonic acid (JA) and salicylic acid (SA), and carbon-based defences over 24 hr. 2) We exposed H. armigera larvae to B. distachyon plants grown under three conditions: +Si, -Si, or treated with Si only once H. armigera feeding began. We measured the effect of short-term plant exposure to Si on H. armigera performance and plant resistance.
3) MeJA-induced Si accumulation occurred as early as 6 hr after treatment via increased JA concentrations. Si supplementation decreased SA concentrations, which could have implications on additional downstream defences. We show a trade-off between Si and phenolics in untreated plants, but this relationship was weakened upon MeJA treatment. Although foliar Si concentrations remained lower, within 72 hr of exposure to Si, plants obtained virtually the same level of resistance to H. armigera as plants exposed to Si for over 30 days. H. armigera feeding also accelerated Si deposition after 6 hr of exposure to Si, however, in as little as 24 hr, levels of Si deposition were similar to plants exposed to Si long term.
4) In addition to its well-documented role as a long-term defence against herbivores, we demonstrate that, over short-term temporal scales, Si accumulation responds to herbivore signals and impacts on plant defence machinery. Further, we provide novel evidence that plants can rapidly incorporate Si into their tissues to mitigate the adverse effects of herbivory as effectively as plants exposed to Si long term.

How to cite: Waterman, J., Cibils-Stewart, X., Hall, C., Mikhael, M., Cazzonelli, C., Hartley, S., and Johnson, S.: Rapid silicon accumulation affects carbon-based plant defences and enhances plant resistance to a global insect pest , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3733, https://doi.org/10.5194/egusphere-egu21-3733, 2021.

Ximena Cibils-Stewart et al.

Grasses accumulate large concentrations of silicon (Si) which alleviates a range of stresses including defence against herbivores. Likewise, grasses symbiotically associate with foliar Epichloë-fungal endophytes which provide herbivore defence, mainly via the production of alkaloids. Some Epichloë-endophytes increase foliar Si concentrations, particularly in tall fescue (Festuca arundinacea) but also in perennial ryegrass (Lolium perenne); it is unknown whether this impacts herbivores. Likewise, while Si is primarily a physical defence against herbivores, it can also affect defensive secondary metabolites; Si supply might therefore also affect alkaloids produced by Epichloë-endophytes, however, this remains untested. We grew tall fescue and perennial ryegrass in a factorial combination with or without Si supplementation, in the absence or presence of a chewing herbivore; Helicoverpa armigera. Grasses were associated with four different Epichloë-endophyte strains (tall fescue: AR584; perennial ryegrass: AR37, AR1, or wild type) or as Epichloë-free controls. Specifically, we assessed how Si supply and Epichloë-endophyte presence impacts plant growth and chemistry, and how their interaction with herbivory affects foliar Si concentrations and alkaloid production. Subsequently, their effects on H. armigera relative growth rates (RGR) were evaluated. In Fescue, the AR584-endophyte increased constitutive (herbivore-free) and induced (herbivore-inoculated) silicon concentrations when Si was supplied. In perennial ryegrass, AR37-endophyte increased constitutive and induced silicon concentration, meanwhile, AR1-endophyte increased constitutive levels only. Si supply and herbivory did not affect alkaloids produced by AR584- or AR1/Wt-endophyte in tall fescue and perennial ryegrass, respectively. However, Si suppressed herbivore-induced production of alkaloids in the AR37-endophyte perennial ryegrass association. Si was a more effective defence in tall fescue than perennial ryegrass, significantly reducing H. armigera RGR. Our results suggest that Si reduced herbivore performance to such an extent in tall fescue that it was operating at maximum effect and endophyte-mediated increases in Si concentration made no further difference. Si had a more modest impact on herbivores in perennial ryegrass, potentially linked to silicon decreasing herbivore feeding and thus, suppressing herbivore-induced alkaloids. We provide novel evidence that increased Si concentrations in some cases interact with endophyte-produced chemical defences, which could ultimately impact plant resistance to herbivores.   

How to cite: Cibils-Stewart, X., Mace, W. J., Popay, A. J., Hartley, S. E., Lattanzi, F. A., Hall, C. R., Powell, J. R., and Johnson, S. N.: Epichloë-endophytes increase constitutive and herbivore-induced silicon defences in grasses but do not directly increase grass resistance to a chewing insect herbivore, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10431, https://doi.org/10.5194/egusphere-egu21-10431, 2021.

Tarikul Islam et al.

In recent years, silicon (Si) has been increasingly linked to biotic stress management in plants including insect herbivory. The effectiveness of Si against chewing insects is now well recognized. Silicification of plant tissues makes them abrasive and tougher, reducing their masticability and digestibility to insect herbivores. This can cause mandibular wearing of chewers and affect their growth and feeding. Although there has been extensive research on the effects of Si on plant defences (i.e. antixenosis and antibiosis), it remains unclear how feeding on silicified plants affects insect defences to their natural enemies. Insect herbivores show morphological and behavioural defences when encountering predators and parasitoids. For example, lepidopteran larvae can regurgitate, twist the body, or even drop off the plants when attacked by natural enemies. Moreover, insects possess innate immunity (physiological defence) against the attackers, demonstrating cellular and humoral responses upon attack. Notably, there could be potential trade-offs between different defence and immunity traits. Given that feeding on Si-rich plants affects insect growth rates, this could impact their relative investment in different defences, thereby making insects more susceptible to their enemies. We are investigating the effects of Si on plant resistance and tolerance to herbivory and its cascading effects on insect defences to their enemies. We have been growing the model grass, Brachypodium distachyon, a high Si-accumulator, hydroponically with or without Si and examining the effects of Si against the global insect herbivore, Helicoverpa armigera. Our preliminary results suggest that Si supplementation enhances plant antixenotic and antibiotic traits and increases plant tolerance to herbivory. We are currently exploring insect defence and immunity traits when fed on silicified versus non-silicified plants. Our study would shed light on the impacts of Si on insects’ susceptibility to biocontrol agents and provide a better understanding of the effects of Si on insect-plant-natural enemy interactions.

How to cite: Islam, T., Moore, B. D., and Johnson, S. N.: Is silicon a double-edged sword against insect herbivores? , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10497, https://doi.org/10.5194/egusphere-egu21-10497, 2021.

Rencheng Li et al.

Abstract: 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 Dendrocalamus ronganensis 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). 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.

Keywords: Dendrocalamus ronganensis; phytolith; phytolith-occluded carbon; soil drought

How to cite: Li, R., Wen, M., Tao, X., Vachula, R. S., Tan, S., Dong, H., and Zhou, L.: Drought influences the phytolith morphology variation and its occluded carbon of leaves in Dendrocalamus Ronganensis during growing season, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-180, https://doi.org/10.5194/egusphere-egu21-180, 2020.

Ryosuke Nakamura et al.

Decomposition of plant leaves is influenced by multiple traits, however, discrete structures of Si such as silicious trichomes on the leaf surface have been overlooked, although similarly to defense against insect herbivores, trichomes are thought to protect leaves from decomposers. This study hypothesized that silicious trichomes slow down leaf decomposition by soil meso- and macrofauna. We used two mesh bags (<0.2 mm and 5 mm) and examined ash-free mass loss of green leaves of Broussonetia papyrifera and Morus australis, closely related Moraceae species apparently different in trichome size and density, after 25 days of decomposition in a common garden. We also measured 10 traits of initial leaves and performed microscopic observation of the leaf surface with an energy dispersive X-ray analyzer. Of the leaf traits, trichome density on the lower leaf surface differed greatly between the two species. Our microscopic observation showed that short trichomes densely arranged on the lower leaf surface of B. papyrifera were highly silicified and that some of long trichomes were also composed of calcium. Ash-free mass loss of M. australis was greater in 5-mm mesh bag than in <0.2-mm mesh bag, while that of B. papyrifera did not differ by mesh size, which represents a suppressive effect of silicious trichomes on decomposition by meso- and macrofauna. The trichomes of B. papyrifera remained apparently intact on the decomposed surface, supporting a view of their continuously deferring influence on the large decomposers during the experimental period. For the meso- and macro-detritivore community, three taxa (Acari, Collembola and Isopoda) showed high population density in the common garden. Overall, our results suggest that distinct forms of Si bodies in plants such as trichomes are worth considering in better understanding of leaf decomposition by meso- and macrofauna.

How to cite: Nakamura, R., Amada, G., Kajino, H., Morisato, K., Kanamori, K., and Hasegawa, M.: How do silicious trichomes influence leaf decomposition by meso- and macrofauna?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-643, https://doi.org/10.5194/egusphere-egu21-643, 2021.

Thomas Guzman et al.

It is widely observed that silicon availability (Si) can enhance plant growth and increase the tolerance of plants to a range of biotic and abiotic stresses, although the specific mechanisms underlying these positive effects are not always understood. Silicon is acquired by plants both actively via transporters located in roots and/or passively as plants transport water during transpiration. The relative importance of each of these mechanisms depends strongly on the plant species and the level of stress experienced by the plant. Currently there is a lively debate in the literature regarding the relationship between plant Si accumulation and transpiration rates. Rates of transpiration can affect the amount of Si moving through a plant and in turn the concentration of available Si in soils can make the plant less vulnerable to the effects of drought stress. In order to better understand these relationships between plant water fluxes and Si accumulation in leaves, nine angiosperm tree species (from five families including both deciduous and evergreen species) were grown in a greenhouse and exposed to contrasting watering treatments. For each species, three trees were well watered throughout the growing season whilst three others were exposed to water stress. Whole plant transpiration fluxes were monitored continuously with balances, and pre-dawn leaf water potentials were measured regularly during the experiment. In addition the foliar Si concentrations of each plant were measured by ICP-AES after alkaline fusion both at the beginning and the middle of the growing season. In this presentation, we show our first results examining the relationship between leaf Si concentrations and plant water fluxes in contrasting species. We tested the hypothesis that drought stress significantly decreased the foliar Si concentration in all of the species measured and that foliar Si concentrations were correlated with the cumulative transpiration rates of plants and thus expected to increase significantly over the growing season. 

How to cite: Guzman, T., Burlett, R., Delvigne, C., Parise, C., Dubois, S., Martin-Gomez, P., Opfergelt, S., and Wingate, L.: Impact of transpiration rates on foliar silicon concentrations across a range of angiosperm species exposed to water stress., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7891, https://doi.org/10.5194/egusphere-egu21-7891, 2021.

Alin Song et al.

Returning crop straw into soil is an important practice to balance biogenic and bioavailable silicon (Si) pool in paddy, which is crucial for rice healthy growth. However, it remains elusive how straw return affects Si bioavailability, its uptake, and rice yield, owing to little knowledge about soil microbial communities responsible for straw degradation. Here, we investigated the change of soil Si fractions and microbial community in a 39-year-old paddy field amended by a long-term straw return. Results showed that rice straw-return significantly increased soil bioavailable Si and rice yield to from 29.9% to 61.6% and from 14.5% to 23.6%, respectively, compared to NPK fertilization alone. Straw return significantly altered soil microbial community abundance. Acidobacteria was positively and significantly related to amorphous Si, while Rokubacteria at the phylum level, Deltaproteobacteria and Holophagae at the class level were negatively and significantly related to organic matter adsorbed and Fe/Mn-oxide combined Si in soils. Redundancy analysis of their correlations further demonstrated that Si status significantly explained 12% of soil bacterial community variation. These findings suggest that soil bacteria community and diversity interact with Si mobility via altering its transformation, resulting in the balance of various nutrient sources to drive biological silicon cycle in agroecosystem.

How to cite: Song, A., Li, Z., and Fan, F.: Soil bacterial communities interact with silicon fraction transformation and promote rice yield after long-term straw return, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-760, https://doi.org/10.5194/egusphere-egu21-760, 2021.

Dongmei Jie et al.

  Phytolith provides a new preconstruction and interpretation of palaeovegetation in either forest or grassland regions. In particular, the phytolith reliability records in both vegetation types should be assessed when they are employed on palaeovegetation reconstruction in north temperate region. Yet this issue has not been clearly investigated. Being two vegetation types (including forest and grassland) in northeast China (NE China) where it is an integrated physical geography unit, they provide some crucial references regarding the phytolith reliability. Thus, we firstly focused the study site of NE China to collect 108 topsoil samples from five dominant community types in forest region and 154 topsoil samples from four dominant community types in grassland region, respectively, to their phytolith assemblages. This study was to establish the reference databases of modern soil phytolith to demonstrate their record reliability. These phytolith data thus better serve palaeovegetation reconstruction in sedimentary sequences using their corresponding vegetation types in two selected regions.

    Analytical results showed that topsoil phytolith assemblages and their phytolith indices (Iw, Ic and W/G) varied substantially with different vegetation types in NE China; phytolith indices were also variations aligned with vegetation compositions. These finding suggest that phytolith is a reliable proxy using reconstructing palaeovegetation.

  The palaeovegetation reconstruction based on these phytolith reference databases indicated that NE China had experienced substantial vegetation changes since the late-glacial period. Community types in forest region may have experienced a succession sequence from the open Larix mixed forest to the open woodland, then turning to the closed broadleaf forest, and finally to the closed Pinus koraiensis mixed forest. In particular, we found that vegetation types in grassland region was dominated by a flourish C3 grass steppe since late-glacial period, with a total coverage higher than 50%. The coverage of C3 grass and C4 grass were higher than 25% and 16%, respectively.

  The palaeovegetation interpretation using these phytolith reference databases since the late-glacial period were consistent with that reconstructed using pollen assemblages in the same stratigraphic profile, confirming the phytolith reliability for reconstructing vegetation type and community type in the NE China. Phytolith record analysis also provided some detailed vegetation information such as the vegetation composition of the understory and Larix abundance in forest region, and the proportion of C3/C4 grass, their biomass and community coverage in grassland region.

  Thus, this study demonstrates the phytolith reliability to provide new perspectives on palaeovegetation reconstruction in northern temperate regions. Furthermore, this finding acts as a potential reference for exploring the relationship between phytolith and (palaeo)vegetation in other temperate regions.

(Supported by the National Natural Science Foundation of China (Grant No.41971100,41771214 )

How to cite: Jie, D., Gao, G., and Li, D.: Reliability of phytoliths for reconstructing vegetation dynamics in northeast China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-308, https://doi.org/10.5194/egusphere-egu21-308, 2020.

Rocky Putra et al.

Plants associate with bacteria over the course of evolution. For example, leguminous plants (Leguminosae/Fabaceae) have evolved a distinct symbiosis with nitrogen-fixing bacteria (rhizobia) about 60 million years ago. Rhizobia are housed in specialised root structures, the nodules, and provide the host plants with available nitrogen. In exchange, the host plant rewards rhizobia with carbon-based compounds. The legume-rhizobia symbiosis differs from being mutualistic to somewhat parasitic. One of the driving factors of that is soil nutrients, e.g. silicon (Si). Yet, the functional role of Si in legumes is largely overlooked.

Previous studies suggest that Si has positive impacts on the legume-rhizobia symbiosis. For example, existing literature demonstrates that Si alleviates a broad range of environmental stresses. Crucially, there is a growing number of studies reporting that Si promotes symbiotic traits, such as increased root nodulation and nitrogen fixation across several leguminous species. To better understand this, a conceptual framework was recently proposed. It is hypothesised that Si uptake and accumulation (silicification) in plant tissues may compensate the high metabolic expenditure of carbon in cell wall formation, accelerate solute transport and gas exchange in the nodules, and protect the plants against stresses.

To investigate the impacts of Si enrichment on functional traits in legumes, a glasshouse experiment was conducted with a model legume, barrel medic (Medicago truncatula) associated with a rhizobial (Ensifer meliloti) strain SM1021. Three plant genotypes were either enriched with Si (+Si) or untreated (-Si). Furthermore, a suite of key functional traits broadly grouped as plant growth, physiology, elemental chemistry, nodule activity and nitrogen fixation were quantified using several analytical/chemical techniques. Si enrichment altered several traits depending on plant genotype and symbiosis with rhizobia. For example, nodule activity was generally promoted in +Si relative to -Si plants, but with a more profound impact in one specific genotype (Sephi). This promotion was correlated positively with silicification either in the foliar or nodule depending on plant genotype.

To examine a context dependency of Si impacts in legumes, a full-factorial experiment in a glasshouse was undertaken with the same model legume (two genotypes) and two rhizobial strains, i.e. SM1021 and SM1022, which the former strain is less effective than the latter. Each host-rhizobial association was supplemented with and without Si and challenged with the foliar-chewing cotton bollworm (Helicoverpa armigera) for a 5-day larval infestation (+herbivore and -herbivore). At 30-day post infestation, plants were harvested and further analysed for nodule traits and plant chemistry. Silicon enrichment strongly increased nodule numbers in both rhizobial strains but only in -herbivore plants and this impact was wiped out in +herbivore plants. However, foliar Si was induced only in +Si relative to -Si in +herbivore plants and the reverse was true for foliar C that might indicate a trade-off between Si and C following herbivory. In addition, Si enrichment generally promoted total soluble protein. Finally, when foliar amino acids (AAs) were clustered into essential, non-essential and total compounds, Si enrichment consistently promoted AAs only when herbivory was absent and shifted to a lesser extent when herbivory was present.

How to cite: Putra, R., Powell, J. R., Hartley, S. (. E., and Johnson, S. N.: Overlooked interactions between the leguminous plant and silicon: Concepts, contexts and consequences, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13562, https://doi.org/10.5194/egusphere-egu21-13562, 2021.

Jinqi Dai et al.

Crop dispersal has long been recognised as an important topic in agricultural archaeology and food globalisation. One of most pressing questions facing archaeologists is determining when and where millet arrived in the South China Coast. Our study focused on the millet phytoliths remains from three Neolithic sites in southeast coastal Fujian. Multiple dating methods, including charred carbon dating, phytolith carbon dating, and optically stimulated luminescence were used to construct the chronologies of the sites. The dating results showed that BTS was initially occupied at approximately 5,500 cal a BP. The millet phytoliths recovered in this study are likely the earliest millet remains found in Fujian, suggesting that millet arrived in the South China Coast at least 5,500 years ago. However, questions about whether millet agriculture in northern China dispersed southward through the inland or coastal routes remain unanswered. Given that millet remains were found in Jiangxi and northern Fujian – two important gaps in the inland route – no earlier than 5,000 cal a BP, it seems that the millet remains recovered from the coastal sites of Fujian might have dispersed following a coastal route from northern China. Nevertheless, Fujian is an important junction of the coastal route for the dispersal of millet from northern China. These findings not only provide new insights to millet dispersal routes in China, but also have significant implications for crop communications between Taiwan and mainland China during the Neolithic age.



How to cite: Dai, J., Cai, X., Jin, J., Ge, W., Huang, Y., Wu, W., Xia, T., Li, F., and Zuo, X.: Millet arrived in the South China Coast around 5,500 years ago, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8311, https://doi.org/10.5194/egusphere-egu21-8311, 2021.

Vincent Ayieko and Rivka Elbaum

Plants produce silica in large quantities, up to 2-10% per dry weight, depending on growth conditions and plant species. The roots absorb monosilicic acid from the soil, and it is transported with water and distributed in nearly all plant tissues. With evapotranspiration, the silicic acid solution is concentrated, and eventually silica forms at leaf epidermis. Nonetheless, the distribution of silica deposits is not uniform within plant tissues. This suggests that there are biological processes that control the deposition of the mineral. In a recent work, the protein Siliplant1 (Slp1) was discovered to precipitate silica in plants. Slp1 is expressed in sorghum leaf epidermal cells called silica cells. Biological molecules active in silica formation typically present positive charge moieties and form some 3D aggregation pattern that allows monosilicic acid to condense into bigger organized structures. Slp1 contains a 24 amino acid N-terminal signal peptide, followed by 124 amino acid linking sequence and a 7-repeat sequence. Slp1 without the signal peptide and a short, conserved peptide appearing five times in Slp1 precipitate silica in vitro. However, the activity of other parts of Slp1 in silica precipitation remains unknown. To analyze sequence motifs that precipitate silica, we synthesized segments of the repeating sequence in Slp1, and characterized the precipitation reactions by yield and spectroscopy. Thermal gravimetric and electron microscopy analyses are planned. Preliminary results show that the most conserved region in the repeating sequence precipitates silica at a concentration range of 1-1.5 mg/mL in a 100 mM silicic acid solution. Under buffered conditions, this peptide is positively charged, precipitating silica at pH between 6 and 7. In contrast, silica-gel formed at pH 8 or 5 after overnight incubation. In comparison, the full length Slp1 (missing the signal peptide) precipitates silica at an estimated concentration of 2.9 mg/mL and pH 6-8. Peptides flanking the conserved sequence did not precipitate silica. Precipitation reactions with combinations of peptides precipitated silica only when the conserved peptide was mixed with the peptide following it at a 1:1 ratio. This part of Slp1 presents –OH moieties that may interact with silica. The reaction produced silica gel as well as silica. When the conserved region was mixed with a preceding peptide, only silica-gel formed. This region presents acidic groups that may block the positive charge on the conserved region. We conclude that the conserved peptide is the only part of the Slp1 repeating region that actively precipitates silica. The peptides flanking the conserved region are not directly involved in silica precipitation.  However, they may allow silica precipitation at increased pH, as seen in the full length Slp1. Further investigation is planned to understand their roles in silica formation.

How to cite: Ayieko, V. and Elbaum, R.: Learning Principles in the Biochemistry of Plant Silica Precipitation , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10976, https://doi.org/10.5194/egusphere-egu21-10976, 2021.

Nerya Zexer and Rivka Elbaum

Silicon oxides are the most abundant mineral group in soils. Therefore, plant roots are always exposed to some silicic acid (Si(OH)4), which is the soluble form of silicates. Monosilicic acid molecules are taken up by roots, carried in the xylem, and subsequently polymerize to silica in varied silicifying target sites. This biogenic silica (SiO2·nH2O) can constitute several percent by dry weight in certain plant taxa. However, the mechanisms of its formation remain mostly unknown. In the roots of sorghum (Sorghum bicolor), silica aggregates form in an orderly pattern along the cell walls of endodermis cells. To investigate the structure and composition of root silica aggregates, we studied their development along roots of hydroponically grown sorghum seedlings. By using Raman micro-spectroscopy, auto-fluorescence, and scanning electron microscopy, we found that putative silica aggregation loci could be identified in roots grown under Si starvation. These micrometer-scale spots were constructed of tightly packed modified lignin and were capable of nucleating trace concentrations of silicic acid. Substantial variation in cell wall auto-fluorescence between roots grown with and without silicic acid demonstrated the impact of silicon on cell wall chemistry. Taken together, this work demonstrates a high degree of control over lignin and silica deposition in cell walls. Such regulation implies an important, yet unknown, function for silicon in plant biology.

How to cite: Zexer, N. and Elbaum, R.: Silica formation in sorghum (Sorghum bicolor) roots, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12176, https://doi.org/10.5194/egusphere-egu21-12176, 2021.

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