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Anne Alexandre - One of the best experts on this subject based on the ideXlab platform.

  • Effects of leaf length and development stage on the triple oxygen isotope signature of grass leaf water and Phytoliths: insights for a proxy of continental atmospheric humidity
    Biogeosciences, 2019
    Co-Authors: Anne Alexandre, Elizabeth Webb, Amaelle Landais, Clément Piel, Sebastien Devidal, Corinne Sonzogni, Martine Couapel, Jean-charles Mazur,, Monique Pierre, Frederic Prie
    Abstract:

    Continental relative humidity (RH) is a key climate parameter, but there is a lack of quantitative RH proxies suitable for climate model-data comparisons. Recently, a combination of climate chamber and natural transect calibrations have laid the groundwork for examining the robustness of the triple oxygen isotope composition (delta O-'18 and O-17-excess) of Phytoliths, that can preserve in sediments, as a new proxy for past changes in RH. However, it was recommended that besides RH, additional factors that may impact delta'O-18 and O-17-excess of plant water and Phytoliths be examined. Here, the effects of grass leaf length, leaf development stage and day-night alternations are addressed from growth chamber experiments. The triple oxygen isotope compositions of leaf water and Phytoliths of the grass species F. arundinacea are analysed. Evolution of the leaf water delta'O-18 and O-17-excess along the leaf length can be modelled using a string-of-lakes approach to which an unevaporated-evaporated mixing equation must be added. We show that for Phytoliths to record this evolution, a kinetic fractionation between leaf water and silica, increasing from the base to the apex, must be assumed. Despite the isotope heterogeneity of leaf water along the leaf length, the bulk leaf phytolith delta'O-18 and O-17-excess values can be estimated from the Craig and Gordon model and a mean leaf water-phytolith fractionation exponent (lambda(Phyto-LW)) of 0.521. In addition to not being leaf length dependent, delta'O-18 and O-17-excess of grass Phytoliths are expected to be impacted only very slightly by the stem vs. leaf biomass ratio. Our experiment additionally shows that because a lot of silica polymerises in grasses when the leaf reaches senescence (58 % of leaf Phytoliths in mass), RH prevailing during the start of senescence should be considered in addition to RH prevailing during leaf growth when interpreting the O-17-excess of grass bulk Phytoliths. Although under the study conditions O-17-excess(Phyto) do not vary significantly from constant day to day-night conditions, additional monitoring at low RH conditions should be done before drawing any generalisable conclusions. Overall, this study strengthens the reliability of the O-17-excess of Phytoliths to be used as a proxy of RH. If future studies show that the mean value of 0.521 used for the grass leaf water-phytolith fractionation exponent lambda(Phyto-LW) is not climate dependent, then grassland leaf water O-17-excess obtained from grassland phytolith O-17-excess would inform on isotope signals of several soil-plant-atmosphere processes.

  • effects of leaf length and development stage on the triple oxygen isotope signature of grass leaf water and Phytoliths insights for a proxy of continental atmospheric humidity
    Biogeosciences, 2019
    Co-Authors: Anne Alexandre, Amaelle Landais, Clément Piel, Sebastien Devidal, Corinne Sonzogni, Martine Couapel, Jean-charles Mazur,, Monique Pierre, Elizabeth A Webb, Frederic Prie
    Abstract:

    Abstract. Continental relative humidity (RH) is a key climate parameter, but there is a lack of quantitative RH proxies suitable for climate model–data comparisons. Recently, a combination of climate chamber and natural transect calibrations have laid the groundwork for examining the robustness of the triple oxygen isotope composition ( δ′18 O and 17 O-excess) of Phytoliths, that can preserve in sediments, as a new proxy for past changes in RH. However, it was recommended that besides RH, additional factors that may impact δ′18 O and 17 O-excess of plant water and Phytoliths be examined. Here, the effects of grass leaf length, leaf development stage and day–night alternations are addressed from growth chamber experiments. The triple oxygen isotope compositions of leaf water and Phytoliths of the grass species F. arundinacea are analysed. Evolution of the leaf water δ′18 O and 17 O-excess along the leaf length can be modelled using a string-of-lakes approach to which an unevaporated–evaporated mixing equation must be added. We show that for Phytoliths to record this evolution, a kinetic fractionation between leaf water and silica, increasing from the base to the apex, must be assumed. Despite the isotope heterogeneity of leaf water along the leaf length, the bulk leaf phytolith δ′18 O and 17 O-excess values can be estimated from the Craig and Gordon model and a mean leaf water–phytolith fractionation exponent ( λPhyto-LW) of 0.521. In addition to not being leaf length dependent, δ′18 O and 17 O-excess of grass Phytoliths are expected to be impacted only very slightly by the stem vs. leaf biomass ratio. Our experiment additionally shows that because a lot of silica polymerises in grasses when the leaf reaches senescence (58 % of leaf Phytoliths in mass), RH prevailing during the start of senescence should be considered in addition to RH prevailing during leaf growth when interpreting the 17 O-excess of grass bulk Phytoliths. Although under the study conditions 17 O-excess Phyto do not vary significantly from constant day to day–night conditions, additional monitoring at low RH conditions should be done before drawing any generalisable conclusions. Overall, this study strengthens the reliability of the 17 O-excess of Phytoliths to be used as a proxy of RH. If future studies show that the mean value of 0.521 used for the grass leaf water–phytolith fractionation exponent λPhyto-LW is not climate dependent, then grassland leaf water 17 O-excess obtained from grassland phytolith 17 O-excess would inform on isotope signals of several soil–plant-atmosphere processes.

  • from radiocarbon analysis to interpretation a comment on phytolith radiocarbon dating in archaeological and paleoecological research a case study of Phytoliths from modern neotropical plants and a review of the previous dating evidence journal of archaeological science 2015 doi 10 1016 j jas 2015 06 002 by dolores r piperno
    Journal of Archaeological Science, 2016
    Co-Authors: Guaciara M Santos, Anne Alexandre, Christine Prior
    Abstract:

    The paper "Phytolith Radiocarbon Dating in Archaeological and Paleoecological Research: A Case Study of Phytoliths from Modern Neotropical Plants and a Review of the Previous Dating Evidence" by Dolores R. Piperno presents radiocarbon analysis of Phytoliths from modern Neotropical plants collected between 1964 and 2013. The analyses presented were intended to rebut the emerging hypothesis that invokes root-plant uptake, transport and reallocation of soil organic carbon into Phytoliths that has been recently put forward as an explanation for the anomalous radiocarbon (14 C) ages (of hundreds to thousands of years old) reported for modern grass Phytoliths in Santos et al. (2010a, 2012a,b). We believe that the results presented in Piperno (2015) lack methodological rigor, mostly due to the absence of any procedural blank assessment, and that the attempts to disprove the hypothesis of uptake of soil organic matter (SOM) by Phytoliths in Santos et al. (2012a) are not supported by a careful analysis. Rather than supporting the position that 100% of the carbon in Phytoliths is of photosynthetic origin, which allows the use of phytolith carbon (or phytC) as a dating tool, the analysis of 14 C in Phytoliths from modern Neotropical plants presented in the study shows that the 14 C ages are strongly affected by other sources of carbon. In this comment, we carefully reassess the 14 C results in Phytoliths from modern Neotropical plants presented in Piperno (2015) in the context of the 14 C bomb-pulse methodology, SOM ages and turnover rates, and offer an alternative interpretation of the experimental results.

  • a phytolith index as a proxy of tree cover density in tropical areas calibration with leaf area index along a forest savanna transect in southeastern cameroon
    Global and Planetary Change, 2005
    Co-Authors: Laurent Bremond, Anne Alexandre, Christelle Hely, Joel Guiot
    Abstract:

    The aim of the study is to calibrate the phytolith index of tree cover density, D/P (the ratio of ligneous dicotyledons Phytoliths (D) over Poaceae Phytoliths (P)) with Leaf Area Index (LAI) measurements. LAI is the vertically integrated surface of leaves per unit of ground area (m(2) leaves/m(2) ground). Modern soil samples from southeastern Cameroon, collected along a continuous forest-savarina transect, have been analyzed for Phytoliths. Phytolith assemblages and D/P index clearly record the physiognomy of the forest and savanna communities and of the transition between both of them. A highly significant relationship was obtained between D/P and LAI. The relationship between phytolith data and the vegetation transect is also discussed and compared with existing palynological results obtained along the same transect. (c) 2004 Elsevier B.V All rights reserved.

  • Grass water stress estimated from Phytoliths in West Africa
    Journal of Biogeography, 2005
    Co-Authors: Laurent Bremond, Odile Peyron, Anne Alexandre, Joel Guiot
    Abstract:

    Aim This study calibrates the relationship between phytolith indices, modern vegetation structure, and a climate parameter (AET/PET, i.e. the ratio of annual actual evapotranspiration to annual potential evapotranspiration), in order to present new proxies for long-term Quaternary climate and vegetation changes, and model/data comparisons. Location Sixty-two modern soil surface samples from West Africa (Mauritania and Senegal), collected along a latitudinal transect across four bioclimatic zones, were analysed. Methods Two phytolith indices are defined as normalized data: (1) humidity-aridity index [Iph (%) ¼ saddle vs. cross + dumbbell + saddle], and (2) water stress index [fan-shaped index (Fs) (%) ¼ fan-shaped vs. sum of characteristic Phytoliths]. Vegetation structures are delimited according to Iph and Fs boundaries. Bootstrapped regression methods are used for evaluating the strength of the relationship between the two phytolith indices and AET/PET. Additional modern phytolith assemblages, from Mexico, Cameroon and Tanzania are extracted in order to test the calibration established from the West African samples. Accuracy of the AET/PET phytolith proxy is compared with equivalent pollen proxy from the same area. Results Characterization of the grass cover is accurately made through Iph. A boundary of 20 ± 1.4% discriminates tall grass savannas from short grass savannas. Water stress and transpiration experienced by the grass cover can be estimated through Fs. AET/PET is accurately estimated from Phytoliths by a transfer function: AET/PET ¼)0.605 Fs) 0.387 Iph + 0.272 (Iph-20) 2 (r ¼ 0.80 ± 0.04) in the application domain (AET/PET ranging from 0.1 ± 0.04 to 0.45 ± 0.04). Phytolith and pollen estimate with similar precision (r pollen ¼ 0.84 ± 0.04) the AET/PET in the studied area. Conclusions This study demonstrates that we can rely on the phytolith indices Iph and Fs to distinguish the different grasslands in tropical areas. Moreover, a new phytolith proxy of AET/PET, linked to water availability, is presented. We suggest from these results that combining phytolith and pollen proxies of AET/ PET would help to constrain this climate parameter better, especially when phytolith assemblages are dominated by Panicoideae and Chloridoideae C 4-grass Phytoliths, are devoid of Pooideae C 3-grass Phytoliths, and occur with a few tropical ligneous woody dicotyledon Phytoliths. As AET/PET is a bioclimatic indicator commonly used in vegetation models, such a combination would help to make model/data comparisons more efficient.

Zhaoliang Song - One of the best experts on this subject based on the ideXlab platform.

  • a review of carbon isotopes of Phytoliths implications for phytolith occluded carbon sources
    Journal of Soils and Sediments, 2020
    Co-Authors: Shilei Yang, Qian Hao, Hailong Wang, Lukas Van Zwieten, Taoze Liu, Xiaomin Yang, Xiaodong Zhang, Zhaoliang Song
    Abstract:

    Phytolith-occluded carbon (PhytOC) is mainly derived from the products of photosynthesis, which can be preserved in soils and sediments for hundreds-to-thousands of years due to the resilient nature of the amorphous phytolith silica. Therefore, stable and radioactive carbon (C) isotopes of Phytoliths can be effectively utilized in paleoecological and archeological research. However, there still exists debate about the applicability of C isotopes of Phytoliths, as a “two-pool” hypothesis to characterize PhytOC sources has been proposed, whereby a component of the PhytOC is derived from soil organic matter (SOM) absorbed through plant roots. Therefore, it is necessary to review this topic to better understand the source of PhytOC. We introduce the stable and radioactive C isotopic compositions of PhytOC, present the impacts of different extraction methods on the study of PhytOC, and discuss the implications of these factors for determining the sources of PhytOC. Based on this review, we suggest that organic matter synthesized by photosynthesis is the main source of PhytOC. However, it is important to make clear whether and how SOM-derived C present in Phytoliths influence the controversial “too-old” skew and isotopic fractionation. Though the two-pool hypothesis has been proved by many researches, the carbon isotopes of Phytoliths still have potential in paleoecology and archeology, because the main source is photosynthesis and many previous studies put forward the availability of these parameters. This review also shows that phytolith C isotopes may vary with different organic C compounds within Phytoliths, which needs further study at the molecular scale. Different phytolith extraction methods can influence 14C dating results.

  • Phytoliths and phytolith carbon occlusion in aboveground vegetation of sandy grasslands in eastern inner mongolia china
    Science of The Total Environment, 2018
    Co-Authors: Xiaomin Yang, Zhaoliang Song, Qian Hao, Hongyan Liu, Xu Liu
    Abstract:

    Abstract Grasslands play a crucial role in the coupled biogeochemical cycles of carbon (C) and silicon (Si) because they have a large biogenic Si pool (i.e. Phytoliths). In recent decades, desertification has occurred extensively in sandy grasslands due to human activities and to increased aridity as a consequence of climate change. The present study determined the contents of Phytoliths and C occlusion within Phytoliths (PhytOC) in sandy grassland with different vegetation coverage from eastern Inner Mongolia, China and preliminarily assessed the effects of desertification on Phytoliths and PhytOC production. Our results showed that the phytolith and PhytOC contents among different plant species varied from 0.68 to 9.23% and 0.03 to 1.13‰, respectively. However, the community-weighted means of the phytolith and PhytOC contents for the total aboveground vegetation were only 1.13–3.61% and 0.09–0.35‰, respectively, and their respective production fluxes ranged from 8.94 to 47.8 kg ha−1 year−1 and from 0.06 to 0.48 kg ha−1 year−1, respectively. As desertification progressed, the total contents of Phytoliths and PhytOC in aboveground vegetation did not change significantly, whereas the production fluxes of Phytoliths and PhytOC were markedly reduced. This study indicates that grassland desertification decreases the range of the total contents of phytolith and PhytOC by reducing species richness, and decreases the production fluxes of Phytoliths and PhytOC by reducing aboveground biomass. Grassland restoration can theoretically enhance the production fluxes of Phytoliths and PhytOC ~ five-fold.

  • functions of Phytoliths in vascular plants an evolutionary perspective
    Functional Ecology, 2016
    Co-Authors: Caroline A E Stromberg, Zhaoliang Song, Veronica S Di Stilio
    Abstract:

    Summary Solid biosilica (Phytoliths) deposited in plant tissues is thought to function as structural support, as a cost-effective alternative to lignin, and in herbivore defence, by limiting nutrient access/extraction and abrading herbivore mouthparts. It has been assumed that active phytolith accumulation evolved for these purposes, but these hypotheses remain untested. For example, an influential idea holds that grasses became so silica-rich through antagonistic co-evolution with mammalian grazers during the Cenozoic. We examine whether Phytoliths fulfil criteria established for adaptations, focusing on three aspects. First, we evaluate the recent debate concerning whether plant silica wears herbivore mouthparts/teeth. Secondly, we test whether the evolutionary pattern of phytolith accumulation is consistent with adaptive hypotheses by mapping silica content onto time-calibrated land plant and grass phylogenies. Thirdly, we compare with palaeontological evidence for the timing of the ‘demand’ for the hypothesized function (structural support, herbivore defence). Our survey demonstrates that Phytoliths meet several criteria for adaptations, but key aspects require further study. For example, Phytoliths wear teeth but are likely less important than dietary grit, suggesting that silica deterrence is ineffective against large mammalian grazers. Mapping analysis indicates that active silica accumulation evolved numerous times, rather than being ancestral in land plants. However, a clear temporal link between these events and hypothesized functional ‘demands’ is still missing. For example, we find no convincing evidence for Cenozoic grass-grazer co-evolution. Synthesis. Phytoliths help support and defend plants today, but the adaptive origin of this trait requires further testing. Such tests should integrate the phylogenetic distributions of Phytoliths with ecology and biomechanics and use fossil evidence to evaluate the correlation between functional ‘demand’ and plant evolution.

  • occurrence turnover and carbon sequestration potential of Phytoliths in terrestrial ecosystems
    Earth-Science Reviews, 2016
    Co-Authors: Zhaoliang Song, Hailong Wang, Kim Mcgrouther
    Abstract:

    Abstract Carbon sequestered in Phytoliths, the silicified features of plants, may accumulate in soils and sediments for several hundreds to thousands of years depending mainly on the morphology and chemical composition of Phytoliths and environmental conditions. Phytolith carbon sequestration is thought to be one of the key biogeochemical carbon sequestration mechanisms. This review summarizes the current state of understanding of occurrence, turnover and carbon sequestration potential of Phytoliths in terrestrial ecosystems. The accumulation rate of Phytoliths in soils is controlled not only by plant litter inputs but also by geochemical stability and turnover of Phytoliths. Most of the organic carbon in Phytoliths is from photosynthesis of atmospheric carbon dioxide (CO 2 ) during formation of Phytoliths. Phytolith carbon sequestration in terrestrial ecosystems is a promising biogeochemical carbon sequestration mechanism and may contribute to the mitigation of global climate warming. Further questions such as the turnover of Phytoliths with different properties and under different environmental conditions, the relative contribution of different ecosystems to the global terrestrial phytolith carbon sequestration, and the cost and potential of each management measure to enhance phytolith carbon sequestration should be investigated.

  • impact of rice cultivar and organ on elemental composition of Phytoliths and the release of bio available silicon
    Frontiers in Plant Science, 2014
    Co-Authors: Zhaoliang Song, Jeanthomas Cornelis
    Abstract:

    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.

Dolores R Piperno - One of the best experts on this subject based on the ideXlab platform.

  • phytolith radiocarbon dating in archaeological and paleoecological research a case study of Phytoliths from modern neotropical plants and a review of the previous dating evidence
    Journal of Archaeological Science, 2016
    Co-Authors: Dolores R Piperno
    Abstract:

    Abstract Recent carbon-14 studies of Phytoliths from modern plants collected from extra-tropical regions of the world have yielded dates that are too old by several hundred to thousands of years. These findings have prompted questions about the suitability of phytolith-derived carbon for dating in archaeological and paleo-environmental research. In this paper, phytolith 14 C ages are determined from a number of modern Neotropical plant taxa collected between 1964 and 2013. The specimens studied are maize ( Zea mays L.), two squash species ( Cucurbita ecuadorensis H.C.Cutler & Whitaker and C. ficifolia Bouche), and two trees common in Neotropical forest, Hirtella americana L. and Socratea durissima (Oersted) H. Uendl. They represent families, genera, and species that are well-represented in Neotropical archaeological and paleoecological sediments. Every phytolith sample returned a post-bomb 14 C phytolith age reflecting collection after 1955, with the exception of a herbarium specimen that was treated with chemicals containing radiocarbon-dead carbon. The phytolith dates do not indicate a source of extraneous old or young carbon occurring on the surfaces or inside of Phytoliths that bias their ages. Such findings are also reflected by previous phytolith 14 C studies of ancient Neotropical sites. Possible reasons for the differences in results between these and other studies and varying interpretations of soil and sediment phytolith 14 C analyses by different investigators are discussed.

  • Phytoliths a comprehensive guide for archaeologists and paleoecologists
    2006
    Co-Authors: Dolores R Piperno
    Abstract:

    1 The Production, Deposition, and Dissolution of Phytoliths 2 Phytolith Morphology 3 Phytoliths in Domesticated Plants and Their Wild Ancestors 4 Field Techniques and Research Design 5 Laboratory Techniques 6 The Interpretation of Phytolith Assemblages: Method and Theory 7 The Role of Phytoliths in Archaeological Reconstruction 8 The Role of Phytoliths in Paleoecology

  • evidence for the control of phytolith formation in cucurbita fruits by the hard rind hr genetic locus archaeological and ecological implications
    Proceedings of the National Academy of Sciences of the United States of America, 2002
    Co-Authors: Dolores R Piperno, Irene Holst, Linda Wesselbeaver, Thomas C Andres
    Abstract:

    Many angiosperms, both monocotyledons and dicotyledons, heavily impregnate their vegetative and reproductive organs with solid particles of silicon dioxide (SiO2) known as opaline Phytoliths. The underlying mechanisms accounting for the formation of Phytoliths in plants are poorly understood, however. Using wild and domesticated species in the genus Cucurbita along with their F1 and F2 progeny, we have demonstrated that the production of large diagnostic Phytoliths in fruit rinds exhibits a one-to-one correspondence to the lignification of these structures. We propose that phytolith formation in Cucurbita fruits is primarily determined by a dominant genetic locus, called hard rind (Hr), previously shown to code for lignin deposition. If true, this evidence represents a demonstration of genetic control over phytolith production in a dicotyledon and provides considerable support to hypotheses that silica Phytoliths constitute another important system of mechanical defense in plants. Our research also identifies Hr as another single locus controlling more than one important phenotypic difference between wild and domesticated plants, and establishes rind tissue cell structure and hardness under the effects of Hr as an important determinant of phytolith morphology. When recovered from pre-Columbian archaeological sites, Cucurbita Phytoliths represent genetically controlled fossil markers of exploitation and domestication in this important economic genus.

  • Phytoliths in cucurbita and other neotropical cucurbitaceae and their occurrence in early archaeological sites from the lowland american tropics
    Journal of Archaeological Science, 2000
    Co-Authors: Dolores R Piperno, Thomas C Andres, Karen E Stothert
    Abstract:

    Cucurbita spp. (squashes and gourds), together with bottle gourd (Lagenaria siceraria), were among the earliest plants manipulated and domesticated in the Americas. Although at least one squash species,Cucurbita moschata , was domesticated in the lowland Neotropics, little is known about its history because preservation of plant remains in sites from the tropical forest is poor. Phytolith analysis has the potential to help in our understanding of early cultural uses of Cucurbita and other important Cucurbitaceae in the American tropical forest. Phytoliths from the fruits of three modern domesticated Cucurbita species were compared with seven wild species of Cucurbita and 41 species of cucurbits from 22 other genera in the Cucurbitaceae. Cucurbita and Lagenaria Phytoliths are distinctive and they have been recovered from archaeological deposits in the lowland Neotropics dating to the terminal Pleistocene and early Holocene periods. Phytolith evidence indicates that a domesticated Cucurbita was present on the northern South American landscape by at least 7000 bp, and quite possibly by 9000 bp.

  • Phytoliths in the reproductive structures of maize and teosinte implications for the study of maize evolution
    Journal of Archaeological Science, 1993
    Co-Authors: Dolores R Piperno, Deborah M Pearsall
    Abstract:

    Abstract Analysis of Phytoliths from the reproductive structures of maize, teosinte, and Tripsacum indicates that teosinte produces Phytoliths differentiable from both of its near relatives. Phytoliths from the cobs of Argentine popcorn, a primitive race thought to more closely resemble the earliest archaeological maize from the Tehuacan Valley, Mexico, than any extant race thus far examined, provide signatures that may be unique to maize. Phytoliths from reproductive structures in Zea should provide a means of discrimination between teosinte and maize in the archaeological record and study of the earliest evolution of maize. Such aspects as loci of cellular silicification and consequent phytolith morphology in teosinte fruitcases and maize cobs support hypotheses of maize evolution that call for morphological change of fruitcases into cobs under human selection.

Frederic Prie - One of the best experts on this subject based on the ideXlab platform.

  • Effects of leaf length and development stage on the triple oxygen isotope signature of grass leaf water and Phytoliths: insights for a proxy of continental atmospheric humidity
    Biogeosciences, 2019
    Co-Authors: Anne Alexandre, Elizabeth Webb, Amaelle Landais, Clément Piel, Sebastien Devidal, Corinne Sonzogni, Martine Couapel, Jean-charles Mazur,, Monique Pierre, Frederic Prie
    Abstract:

    Continental relative humidity (RH) is a key climate parameter, but there is a lack of quantitative RH proxies suitable for climate model-data comparisons. Recently, a combination of climate chamber and natural transect calibrations have laid the groundwork for examining the robustness of the triple oxygen isotope composition (delta O-'18 and O-17-excess) of Phytoliths, that can preserve in sediments, as a new proxy for past changes in RH. However, it was recommended that besides RH, additional factors that may impact delta'O-18 and O-17-excess of plant water and Phytoliths be examined. Here, the effects of grass leaf length, leaf development stage and day-night alternations are addressed from growth chamber experiments. The triple oxygen isotope compositions of leaf water and Phytoliths of the grass species F. arundinacea are analysed. Evolution of the leaf water delta'O-18 and O-17-excess along the leaf length can be modelled using a string-of-lakes approach to which an unevaporated-evaporated mixing equation must be added. We show that for Phytoliths to record this evolution, a kinetic fractionation between leaf water and silica, increasing from the base to the apex, must be assumed. Despite the isotope heterogeneity of leaf water along the leaf length, the bulk leaf phytolith delta'O-18 and O-17-excess values can be estimated from the Craig and Gordon model and a mean leaf water-phytolith fractionation exponent (lambda(Phyto-LW)) of 0.521. In addition to not being leaf length dependent, delta'O-18 and O-17-excess of grass Phytoliths are expected to be impacted only very slightly by the stem vs. leaf biomass ratio. Our experiment additionally shows that because a lot of silica polymerises in grasses when the leaf reaches senescence (58 % of leaf Phytoliths in mass), RH prevailing during the start of senescence should be considered in addition to RH prevailing during leaf growth when interpreting the O-17-excess of grass bulk Phytoliths. Although under the study conditions O-17-excess(Phyto) do not vary significantly from constant day to day-night conditions, additional monitoring at low RH conditions should be done before drawing any generalisable conclusions. Overall, this study strengthens the reliability of the O-17-excess of Phytoliths to be used as a proxy of RH. If future studies show that the mean value of 0.521 used for the grass leaf water-phytolith fractionation exponent lambda(Phyto-LW) is not climate dependent, then grassland leaf water O-17-excess obtained from grassland phytolith O-17-excess would inform on isotope signals of several soil-plant-atmosphere processes.

  • effects of leaf length and development stage on the triple oxygen isotope signature of grass leaf water and Phytoliths insights for a proxy of continental atmospheric humidity
    Biogeosciences, 2019
    Co-Authors: Anne Alexandre, Amaelle Landais, Clément Piel, Sebastien Devidal, Corinne Sonzogni, Martine Couapel, Jean-charles Mazur,, Monique Pierre, Elizabeth A Webb, Frederic Prie
    Abstract:

    Abstract. Continental relative humidity (RH) is a key climate parameter, but there is a lack of quantitative RH proxies suitable for climate model–data comparisons. Recently, a combination of climate chamber and natural transect calibrations have laid the groundwork for examining the robustness of the triple oxygen isotope composition ( δ′18 O and 17 O-excess) of Phytoliths, that can preserve in sediments, as a new proxy for past changes in RH. However, it was recommended that besides RH, additional factors that may impact δ′18 O and 17 O-excess of plant water and Phytoliths be examined. Here, the effects of grass leaf length, leaf development stage and day–night alternations are addressed from growth chamber experiments. The triple oxygen isotope compositions of leaf water and Phytoliths of the grass species F. arundinacea are analysed. Evolution of the leaf water δ′18 O and 17 O-excess along the leaf length can be modelled using a string-of-lakes approach to which an unevaporated–evaporated mixing equation must be added. We show that for Phytoliths to record this evolution, a kinetic fractionation between leaf water and silica, increasing from the base to the apex, must be assumed. Despite the isotope heterogeneity of leaf water along the leaf length, the bulk leaf phytolith δ′18 O and 17 O-excess values can be estimated from the Craig and Gordon model and a mean leaf water–phytolith fractionation exponent ( λPhyto-LW) of 0.521. In addition to not being leaf length dependent, δ′18 O and 17 O-excess of grass Phytoliths are expected to be impacted only very slightly by the stem vs. leaf biomass ratio. Our experiment additionally shows that because a lot of silica polymerises in grasses when the leaf reaches senescence (58 % of leaf Phytoliths in mass), RH prevailing during the start of senescence should be considered in addition to RH prevailing during leaf growth when interpreting the 17 O-excess of grass bulk Phytoliths. Although under the study conditions 17 O-excess Phyto do not vary significantly from constant day to day–night conditions, additional monitoring at low RH conditions should be done before drawing any generalisable conclusions. Overall, this study strengthens the reliability of the 17 O-excess of Phytoliths to be used as a proxy of RH. If future studies show that the mean value of 0.521 used for the grass leaf water–phytolith fractionation exponent λPhyto-LW is not climate dependent, then grassland leaf water 17 O-excess obtained from grassland phytolith 17 O-excess would inform on isotope signals of several soil–plant-atmosphere processes.

Changsui Wang - One of the best experts on this subject based on the ideXlab platform.

  • point count estimation of articulated husk Phytoliths of foxtail millet and its prospective use in agricultural archaeology
    Quaternary International, 2016
    Co-Authors: Xue Shang, Xin Wang, Pengfei Sheng, Changsui Wang
    Abstract:

    Abstract Many researchers have focused on the precise identification of Phytoliths extracted from archaeological samples, and on the extraction methods of phytolith from all kinds of samples as well. Additionally, it is important to perfect the scientific method of phytolith quantification. Phytoliths, especially from the husk, are easily broken after being long-buried or during extraction treatment. These can result in uncertainties about quantification of grain numbers and varies under different conditions. Here we introduce a method of point count estimation of articulated millet husk Phytoliths, and evaluate its accuracy. As a result, we successfully used the point count method into estimating the area of husk phytolith in unit weight of modern millet samples, which will broaden the available data in archaeobiological research. We suggest precise estimations can therefore be done with this method.

  • comparison of dry ashing and wet oxidation methods for recovering articulated husk Phytoliths of foxtail millet and common millet from archaeological soil
    Journal of Archaeological Science, 2014
    Co-Authors: Xin Wang, Hongen Jiang, Xue Shang, Weilin Wang, Yan Wu, Pengcheng Zhang, Changsui Wang
    Abstract:

    Phytolith research on foxtail and common millets represent one of the keys to explore early agricultural activities in the Yellow River basin in China. However, the Phytoliths of these two millets easily disintegrate during burial and the extraction process. In this paper, both dry ashing and wet oxidation methods were applied to determine the effects on phytolith extraction from archaeological soil samples. The results indicated that the dry ashing method had two significant advantages over wet oxidation: (1) the morphology of husk Phytoliths was retained to a greater extent; and (2) nearly all the charcoalified tissues were removed successfully. The dry ashing method proved to be a better method for phytolith extraction of both foxtail millet as well as common millet from archaeological samples. (C) 2014 Elsevier Ltd. All rights reserved.

  • comparison of dry ashing and wet oxidation methods for recovering articulated husk Phytoliths of foxtail millet and common millet from archaeological soil
    Journal of Archaeological Science, 2014
    Co-Authors: Xin Wang, Hongen Jiang, Xue Shang, Weilin Wang, Pengcheng Zhang, Tao Wang, Changsui Wang
    Abstract:

    Abstract Phytolith research on foxtail and common millets represent one of the keys to explore early agricultural activities in the Yellow River basin in China. However, the Phytoliths of these two millets easily disintegrate during burial and the extraction process. In this paper, both dry ashing and wet oxidation methods were applied to determine the effects on phytolith extraction from archaeological soil samples. The results indicated that the dry ashing method had two significant advantages over wet oxidation: (1) the morphology of husk Phytoliths was retained to a greater extent; and (2) nearly all the charcoalified tissues were removed successfully. The dry ashing method proved to be a better method for phytolith extraction of both foxtail millet as well as common millet from archaeological samples.

  • comparing dry ashing and wet oxidation methods the case of the rice husk oryza sativa l
    Microscopy Research and Technique, 2012
    Co-Authors: Yan Wu, Changsui Wang, David V Hill
    Abstract:

    Experiments were conducted to determine the effects that different methods for the preparation of modern plant samples have on the resulting Phytoliths using rice husks (Oryza sp.). The methods that are commonly used in phytolith extraction include (1) dry ashing, (2) acid extraction (3) a combination of both techniques. The results showed that processing methods have an impact on the morphology of two subspecies of rice Phytoliths, dry ashing producing more conjoined cell Phytoliths or multicells Phytoliths than acid extraction. Using a combination of both methods resulted in the presence of fewer conjoined cells than dry ashing alone, but more conjoined cells than acid extraction. Alternative explanations are proposed to explain the formation of conjoined phytolith cells. Microsc. Res. Tech. 75:12721276, 2012. (C) 2012 Wiley Periodicals, Inc.