Phytolith Accumulation Research Articles

Controls for phytolith accumulation in Moso bamboo leaves across China

Phytoliths are amorphous silica formed gradually in plant tissue, which have great potential to mitigate climate change due to their resistance to decomposition and their ability to occlude organic carbon. The accumulation of phytoliths is regulated by multiple factors. However, the factors controlling its accumulation remain unclear. Here, we investigated phytolith content in Moso bamboo leaves of different ages collected from 110 sampling sites of their main distribution regions across China. The controls for phytolith accumulation were studied by correlation and random forest analyses. Our results showed that phytolith content is leaf age-dependent (16-month-old leaf >4-month-old leaf >3-month-old leaf). Phytolith accumulation rate in Moso bamboo leaves is significantly correlated with mean monthly temperature (MMT) and mean monthly precipitation (MMP). About 67.1 % of the variance of the phytolith accumulation rate could be explained by multiple environmental factors, mainly MMT and MMP. Therefore, we conclude that the weather is the major driver that regulates the phytolith accumulation rate. Our study provides a unique dataset for estimating phytolith production rate and the potential carbon sequestration of phytolith through climatic factors.

Microbiomorphs of the soddy solodic planosol and buried organic-accumulative quasi-clay soil of West Siberia

The purpose of the study. Reconstruction of the conditions of solodic soils formation in the forest-steppe zone using soil characteristics and microbiomorphic analysis. Location and time of the study. The study was conducted in the forest-steppe zone (Kulunda, Novosibirsk region, Russia) where in the birch grove a pedocomplex consisting of a surface turf soddy soil and a buried soil. Soil samples were collected in 2014. Methods. Phytolith and some other microbiomorphs morphology, composition and relative abundance were analysed and their soil profile changes accessed. Results. Several peaks of the maximum accumulation of phytoliths were found in the microbiomorphic profile of the soddy solodic planosol. The largest number of phytoliths was found in the eluvial horizon. Phytoliths of steppe gramineous plants and elongated forms of dicotyledonous grasses (forbs, legumes, etc.) accounted for a significant proportion. Diatoms were present throughout the entire soil profile; sponge spicules were rare. Conclusion. At the first stage of its formation the buried soil went through the steppe stage of development (predominance of steppe grasses), followed by overgrowing of the steppe soil with meadow-forest vegetation at the current stage (increased share of forest and meadow grasses). The presence of diatomic shells is typical for soils experiencing recurrent (seasonal) flooding of the birch groves: a lot of snow usually accumulates there, and after the snowmelt water stays for a long time in summer. During wet years, when the groundwater level rises and merges with the surface waters, the phytolith forms characteristic of reeds, sponge spicules, and other indicators of increased moisture increased. Thus, the microbiomorphic composition of the buried organo-accumulative soil reflected its formation.

Effect of Soil Water Contents on Arsenic Accumulation in Phytoliths of Pteris multifida and Phragmites australis

The accumulation of metal(loid)s in phytoliths can physically immobilize the toxic materials and reduce toxicity in plant bodies and soil. Spider brake (Pteris multifida) is a well-known As hyperaccumulator that also harbors phytolith. However, As accumulation in phytoliths has not yet been studied with P. multifida. Soil water content is considered the main factor influencing phytolith accumulation. In this study, the As concentration in the phytoliths of P. multifida was compared with that in common reed (Phragmites australis) phytoliths with various soil water content. The range of As concentration in the phytoliths of P. multifida was 414.70–1610.74 mg kg−1, and the range for P. australis phytoliths was 41.67–126.54 mg kg−1. In P. multifida, higher soil water content increased As accumulation in the phytolith but did not affect the phytolith content in the plant. In P. australis, the higher soil water content increased phytolith content in the plant but decreased As concentration in phytoliths. This study suggests that P. multifida has higher As content in phytoliths than P. australis, and this accumulation can be affected by soil water content. The current findings provide how As encapsulated in phytolith and detoxified in different plants and conditions.

Effect of Soil Characteristics on Arsenic Accumulation in Phytolith of Gramineae (Phragmites japonica) and Fern (Thelypteris palustris) Near the Gilgok Gold Mine

In South Korea, most metal mines were abandoned and caused contamination for more than 30 years. Even the soil is highly contaminated with trace elements, plants still grow in the area and can affect the contamination. Phytolith is amorphous silica in the plant body. Phytolith is resistant to decomposition, and the stabilization of carbon, nutrients, and toxic substances accumulated in the phytolith is being studied. In this study, the Gilgok gold mine, which is contaminated with arsenic was selected as the research site. We selected Phragmites japonica and Thelypteris palustris as targets for the analysis of arsenic accumulation in plants and phytolith. Plants accumulate more phytolith at the riverside. The higher water content of soil increased the Arsenic (As) concentration in the frond of the T. palustris. Soil available silicon (Si) did not affect phytolith accumulation but increased As accumulation in the plant and phytolith. The research result showed that P. japonica and T. palustris have the ability to accumulate As in phytolith and the accumulation can be changed with soil characteristics and plant species. This As accumulation in phytolith can affect plant tolerance in contaminated areas and change the As availability in the soil. The result of the research can be used as a database to build a sustainable environment.

Pen management and livestock activities based on phytoliths, dung spherulites, and minerals from Cova Gran de Santa Linya (Southeastern pre-Pyrenees)

The archaeological evidence from Cova Gran de Santa Linya suggests that during the Late Neolithic and Early Bronze Age, the site was used as a livestock enclosure where the accumulated excrements were burned, generating a sequence known by the term fumier. Here we present the results of an integrated study of silica phytoliths, dung spherulites, and mineral composition of sedimentary matrix from the remaining Holocene sequence. The use of fire to sanitize the space had important consequences for the preservation of dung spherulites and the accumulation of phytoliths. Phytolith assemblages indicate that the animals enclosed in the cave were mostly sheep that exploited the pastures nearby the site during the year. In this sense, the results from our modern plant reference collection challenge the assumption that grass inflorescence phytolith can be used as a seasonality indicator.

Effects of Silicon Fertilization on Soil Chemical Properties and Phytolith Formation of Phyllostachys pubescens

Silicon is benefit to Gramineae plants in growth and resistance to various stresses. However, the effect of silicon fertilizer application on Phyllostachys pubescens is still not investigated yet. Phyllostachys pubescens Mazel ex J. Houz is one kind of Gramineae plants which distributes in a large area. In this study, a field experiment with five Si fertilizer application rates (0, 125, 250, 375, and 500 kg ha-1) was setup in a Phyllostachys pubescens forest in China to examine the effects of Si fertilizer on bamboo Si and phytolith accumulation in fresh leaf and leaf litter. Results showed that Si application increased soil available Si content in deep layers. Si content of leaf-litter increased with the increasing level of Si fertilizer application rate, with the value ranging from 114.3 g kg−1 to 172.7 g kg−1, however, no significant difference was observed in fresh leaf, with the value ranging from 84.0 g kg−1 to 115.0 g kg−1. The phytolith contents of leaf-litter and fresh leaf were consistent with the Si contents, the phytolith content in leaf-litter of T4 (500 kg ha-1) was 48.4% higher than the control, suggesting Phyllostachys pubescens exhibited an increasing carbon sink in phytolith when Si fertilizer applied, which is an effective way to increase long-term soil organic carbon storage in Phyllostachys pubescens forests with a suitable Si fertilization.

Silicon Fertilizer Application Promotes Phytolith Accumulation in Rice Plants.

In this study, a pot experiment was designed to elucidate the effect of varying dosages of silicon (Si) fertilizer application in Si-deficient and enriched paddy soils on rice phytolith and carbon (C) bio-sequestration within phytoliths (PhytOC). The maximum Si fertilizer dosage treatment (XG3) in the Si-deficit paddy soil resulted in an increase in the rice phytolith content by 100.77% in the stem, 29.46% in the sheath and 36.84% in the leaf compared to treatment without Si fertilizer treatment (CK). However, the maximum Si fertilizer dosage treatment (WG3) in the Si -enriched soil increased the rice phytolith content by only 32.83% in the stem, 27.01% in the sheath and 32.06% in the leaf. Overall, Si fertilizer application significantly (p < 0.05) increased the content of the rice phytoliths in the stem, leaf and sheath in both the Si-deficient and enriched paddy soils, and the statistical results showed a positive correlation between the amount of Si fertilizer applied and the rice phytolith content, with correlation coefficients of 0.998 (p < 0.01) in the Si-deficient soil and 0.952 (p < 0.05) in the Si-enriched soil. In addition, the existence of phytoliths in the stem, leaf, and sheath of rice and its content in the Si-enriched soil were markedly higher than that in the Si-deficient soil. Therefore, Si fertilizer application helped to improve the phytolith content of the rice plant.

Conversion from tussock grassland to pine forest: effect on soil phytoliths and phytolith-occluded carbon (PhytOC)

Photolith morphotypes differ between plant species which can be utilized to reconstruct past vegetation. More recently, the role of phytoliths in soil carbon (C) storage and soil C and silicon (Si) cycling has received increasing attention. The aim of this study was to investigate the impact of recent land cover change on soil phytolith assemblage, soil phytolith concentration, and phytolith-occluded carbon (PhytOC) storage. Mineral soil samples (0–10 cm) were collected from a tussock grassland (n = 18) and an adjacent 32-year-old pine forest (n = 21) in Otago, New Zealand. The pine forest was established on tussock grassland. Microwave digestion was followed by sedimentation and flotation procedures to obtain a purified phytolith extract to identify soil phytolith morphotypes by microscopy and to quantify PhytOC concentrations using an elemental analyzer. Soil phytolith assemblage was similar under tussock grassland and pine forest. Bulliform and short cells which were derived from grass species accounted for more than 80% of the phytoliths. Woody plant-derived phytoliths found under tussock grassland (1) may originate from shrubs which are encroaching into the tussock grassland and/or (2) are a legacy of the past woody-dominated vegetation. Soil phytolith concentration ranged between 1 and 3%. Soil PhytOC storage was 0.15 kg C/m2 and 0.14 kg C/m2 under tussock grassland and pine forest, respectively, and accounted for around 3% of total soil carbon storage. Soil phytolith assemblage, soil phytolith concentration, and soil PhytOC storage did not differ significantly between the tussock grassland and the pine forest that was converted from tussock grassland recently. The dominance of grass-derived phytoliths under the pine forest may reflect the legacy of the tussock vegetation which dominated the study site before the afforestation with pine in 1992. This study also revealed that the intrinsic feature of tussock grass species and the accumulation of phytoliths over centuries is likely the cause for the high soil phytolith and PhytOC concentrations.

Phytolith accumulation in broadleaf and conifer forests of northern China: Implications for phytolith carbon sequestration

Carbon (C) occlusion within phytoliths (PhytOC) has a significant potential for long-term C sequestration in forest ecosystems. To unravel the role of forest composition on phytolith production, soil phytolith distribution, and phytolith C sequestration in soils, we investigated community composition and examined phytoliths and PhytOC of mature leaves or needles of dominant trees and understory herbs, as well as soil profiles (50cm depth) within Quercus, Betula, Larix and Pinus forest ecosystems of northern China. Results showed that herb layers contributed 72%, 52%, 40%, and 5% to the flux of phytolith production within Betula forest (18.0±1.26kgha−1yr−1), Quercus forest (28.5±0.77kgha−1yr−1), Larix forest (37.7±1.80kgha−1yr−1) and Pinus forest (16.9±0.30kgha−1yr−1), respectively. The distribution pattern of soil phytoliths from topsoil to subsoil could be classified into three types: significantly decreasing pattern (Betula forest and Quercus forest), non-significantly decreasing pattern (Larix forest), and initially increasing and then decreasing pattern (Pinus forest). Within 0–50cm soil depth, the PhytOC storage of Betula forest, Quercus forest, Larix forest and Pinus forest were 0.29±0.02tha−1, 0.67±0.03tha−1, 0.46±0.03tha−1 and 0.37±0.02tha−1, respectively. Moreover, the soil PhytOC turnover times of these four forest types were estimated to be 537,503,363 and 560year, respectively, which were at least 8–20 times slower than soil organic carbon contributing to climate change mitigation. Overall, our findings indicate that composition of the forest community controls the production flux of phytoliths and the distribution of soil phytoliths, and influences the biogenic silica and its coupled carbon cycles.

Effect of phytoliths for mitigating water stress in durum wheat

The role of silicon (Si) in alleviating biotic and abiotic stresses in crops is well evidenced by empirical studies; however, the mechanisms by which it works are still poorly known. The aim of this study is to determine whether or not phytolith composition and distribution in wheat are affected by drought and, if so, why. Durum wheat was grown using hydroponics in the presence of polyethylene glycol (PEG)-6000 to perform a water-stress simulation. We developed an original method for insitu analysis of phytoliths in leaves via X-ray imaging. PEG was efficient in inhibiting water uptake by roots and creating stress, and prevented a small fraction of Si from being accumulated in the shoots. The application of Si with PEG maintained shoot and root fresh weights (FW) and relative water content at higher values than for plants without Si, especially at PEG 12%. Our data show that, under water stress in the presence of Si, accumulation of phytoliths over the veins provides better support to the leaf, thus allowing for a better development of the whole plant than in the absence of Si. The development of silicified trichomes in durum wheat depends primarily on the availability of Si in soil and is not an adaptation to water stress.

The accumulation of phytolith-occluded carbon in soils of different grasslands

A better understanding of the role of grassland systems in producing and storing phytolith-occluded carbon (PhytOC) will provide crucial information in addressing global climate change caused by a rapid increase in the atmospheric CO2 concentration. Soil samples of typical steppe, meadow steppe, and meadow in Inner Mongolia, China, were taken at 0–10-, 10–20-, 20–40-, and 40–60-cm depths in July and August of 2015. The soil phytoliths were isolated by heavy liquid (ZnBr2), and the soil PhytOC was determined by the traditional potassium dichromate method. The results of our study showed that the storage of soil phytoliths was significantly higher in the meadow (33.44 ± 0.91 t ha−1) cf. meadow steppe (26.8 ± 0.98 t ha−1) and typical steppe (21.19 ± 4.91 t ha−1), which were not different. The soil PhytOC storage was significantly different among grassland types, being: meadow (0.39 ± 0.01 t ha−1) > meadow steppe (0.29 ± 0.02 t ha−1) > typical steppe (0.23 ± 0.02 t ha−1). PhytOC storage in typical steppe soil within the 0–60-cm soil layer is the lowest and that in meadow soils is the highest. The grassland type and the soil condition play significant roles in accumulation of phytoliths and PhytOC in different grassland soils. We suggest that the aboveground net primary productivity (ANPP) is important in soil phytolith accumulation and PhytOC content. Phytolith and PhytOC storages in grassland soil are influenced by factors such as grass type, local climate and soil conditions, and management practices. Management practices to increase grass biomass production can significantly enhance phytolith C sequestration.

Functions of phytoliths in vascular plants: an evolutionary perspective

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.

Intraspecific biogenic silica variations in the grass species Pennisetum pedicellatum along an evapotranspiration gradient in South Niger

Climate influences terrestrial Si and C cycles. To evaluate how drought influences Si dynamics in African savannahs we studied 12 sites along a climatic gradient of precipitation and drought-stress in South Niger. We analysed plant traits and Si (phytolith) content in 12 specimens of a drought adapted grass species (Pennisetum pedicellatum Trin.), and in surface soils. Phytolith/amorphous silica (ASi) was quantified by the 1%Na2CO3 (nc) digestion method, and the acid plus heavy-liquid extraction method (bz). Phytolith morphotypes were also analysed under the microscope. Our results show that with increasing drought-stress (decreasing AET/PET and precipitation, and increasing temperature), ASi in P. pedicellatum (ApSinc and ApSibz) increases, while ASi in soils (AsSibz) decreases. ApSinc shows higher correlation with precipitation of the wettest month (Pwet, r=−0.84, p<0.001), AET/PET (r=−0.73, p<0.01) and length of dry season (r=0.83, p<0.001) than with AsSibz (r=−0.59, p<0.05). Plant height increases with increasing precipitation (r=0.61, p<0.05). Leaf area is positively correlated with AsSibz (r=0.81, p<0.01). Bulliform phytoliths in P. pedicellatum growing under driest climate represent up to 12% of the leaf phytolith assemblage and just 2% in specimens sampled south of ∼13°N at more humid sites. Thus, the abundance of silicified bulliform cells is strongly negatively correlated with Pwet (r=−0.92, p<0.001) and AET/PET (r=−0.93, p<0.001). Other intra-specific variations, e.g. the length of bilobate phytoliths, are not observed along the climatic gradients documented here. We conclude that drought and evapotranspiration rates influence plant height and leaf size, increase Si uptake by the C4 grass P. pedicellatum, and favour silicification of the bulliform (motor) cells triggering leaf movements. In surface soils, greater phytolith accumulation is likely due to higher plant productivity and weaker soil erosion at humid sites.

Dynamics of production and accumulation of phytolith assemblages in the Restinga of Maricá, Rio De Janeiro, Brazil

Abstract The Marica “restinga”, located on the eastern part of Rio de Janeiro State (Brazil), corresponds to one of the few remaining preserved areas of the state's coastal plain. This coastline presents two sand barriers separated by a depression where there is a freshwater swamp and different plant communities distributed in areas of high ecological diversity accompanying the local topography and the range of marine spray. This paper is a study of the soil phytolith assemblages in the Marica restinga, with the intent of establishing reference collections for paleoenvironmental studies of this coastal area during the Quaternary. Phytoliths were chosen as proxies, but their use for reconstruction of this type of vegetation is pioneer research, so it was essential to characterize the phytolith assemblages for each plant community through the identification of the main morphotypes and whether or not they are preserved in coastal depositional environments under the effect of geomorphology and salinity. Eight plant communities, distributed almost parallel to the coastline over sandy barriers, lagoonal plain, lagoon margin and weathered basement were identified: Halophile-psamophile, near the beach; two Scrub communities, one over the Holocene barrier and the other over the Pleistocene barrier; two Herbaceous swamps, one between the two sand barriers, the other behind the Pleistocene barrier; Slack, in front of the Pleistocene barrier; Shrubby vegetation on the shore of Marica lagoon and Dry forest, over the weathered Pre-Cambrian basement. In general, it was found that this type of environment is not very favorable for the formation and accumulation of phytoliths. Restinga plants did not prove to be large producers of phytoliths, except those known as such, as in the case of Poaceae and Cyperaceae. It was also observed that the permanence of phytoliths in sediments is strongly influenced by its particle size and organic matter content. The largest stocks of phytoliths were found in swamp communities, due to the presence of organic matter and low energy dynamics, and in dry forests, where a process of pedogenesis already occurs. Despite the low phytolith stocks present in modern assemblages, they show a high degree of conservation, which enabled significant results for the study of this type of vegetation. The calculated phytolith indices (tree density and water stress) consistently expressed, in detail, the environment of each community analyzed from the point of view of the type of vegetation cover and the conditions of water availability to plants.

Response of Vertisols, Andosols, and Alisols to paddy management

Interchanging submergence and drainage in paddy soils induce alternating redox conditions. It is known that this causes changes in organic carbon stocks, in amounts and crystallinity of Fe oxides as well as transformation of clay minerals and subsequent changes in cation exchange capacity (CEC). However, the influence of the initial soil type on the extent of these changes is not yet well understood. Therefore, we studied paddy soils that derived from three different soil types (Vertisols, Andosols, Alisols) on volcanic parent material in Java (Indonesia). To account for the variability in parent materials, we additionally sampled sandstone-derived Alisols in China. Adjacent non-paddy soils were sampled as references. Samples were analyzed for texture, bulk density, clay mineral composition, total element content, pH, CEC, phosphorus retention, organic carbon (OC), and acid oxalate- (Feox) and dithionite–citrate–bicarbonate-extractable Fe (FeDCB).Only the Alisol-derived paddy soil in China showed textural changes, compared to the non-paddy soil. Evidence for paddy management induced ferrolysis was not found. The smaller topsoil clay content in the paddy soil is most probable caused by clay migration. Only minor differences in clay minerals were found; topsoils of Andosol-derived paddy soils, however, tend to be less desilicated, indicating phytolith accumulation. Except for Vertisols, paddy management caused significant depletion in Fe oxides in the topsoils (puddled layer and plow pan) due to redox processes. The extent to which the reduced Fe was leached or re-oxidized as short range-ordered Fe oxides depended on the soil texture. Andosols and sandy Alisols facilitated leaching, clayey Alisols re-oxidation. In either case, the stocks of crystalline Fe oxides diminished, causing increased proportions of short range-ordered Fe oxides. Retention of phosphorus was directly related to changes in the absolute amounts of short range-ordered Fe oxides. An accumulation of Fe oxides in paddy subsoils was not found. Lateral transport with drainage water might be a reason. In highly permeable soils with large vertical water fluxes (e.g., Andosols under paddy management), colloidal transport might also play a role. Despite losses in potential OC storage capacity (i.e., Fe oxides, clay minerals, allophane), paddy soils derived from Andosols and sandy Alisols in China had larger OC concentrations in the puddled topsoil, whereby the other soils showed no increase in OC under paddy management. Therefore, paddy management does not necessarily enhance carbon sequestration. Rather, differences in organic matter input between non-paddy and paddy soils seem to determine whether OC is accumulated under paddy management or not. Effects of paddy management on CEC were little and mainly due to OC accumulation and Fe oxide coating removal from clay minerals.Overall, paddy management-induced changes were partly influenced by the original soil and the parent material. In turn, the main characteristics of the initial soil type were preserved and not overridden by paddy management.

稻田生态系统中植硅体的产生与积累——以嘉兴稻田为例

Phytolith,the opal of amorphous silica formed in plant tissues( e. g.,cell walls,cell luminas,and intercellular spaces typically near evaporating surfaces),presents in most plants. This study selected plants of five rice cultivars of Jiahua11,Zhejing37, Ning81, Xianghu301, Xiushui09 and their corresponding surface soils( 0—10 cm) at the experiment base of Hangjiahu plain in Jiaxing,to investigate the fluxes of the phytolith production and accumulation in rice ecosystems. The main purpose of this study is to provide scientific reference for understanding the role of phytoliths in biogeochemical cycles of silicon and carbon. Results showed that the phytolith content varied from 40. 54 to 51. 40 g / kg, with an average of 46. 54 g / kg,being higher in Jiahua11,Ning81 and Xianghu 301 than that in Zhejing37 and Xiushui09 It decreased in the following order among different organs: sheath leaf stem root grains. There was a positive correlation between phytolith content and total SiO 2 in rice and soil,R2= 0. 8156( P0. 01) and R2= 0. 355( P0. 05), respectively. The total production flux of phytoliths for whole plants was 1269. 59 kg hm-2a-1. The aboveground and underground phytolith production flux was 1203. 44 and 66. 15 kg hm-2a-1,respectively. The flux of phytolith production differed in different rice cultivars. The flux of aboveground and underground phytolith production in Jiahua11 was higher than that of the other. The flux of phytolith production from root,stem,sheath,leaf and grains is 66. 15,131. 65, 491. 08,185. 36 and 395. 35 kg hm-2a-1,respectively. In rice ecosystems with 50 years of cultivation,the phytolith accumulation flux in surface soil( 0—10 cm) was 40. 38 kg hm-2a-1,which was equivalent to the flux of root phytolith production,implying that the rice straws are rarely returned to the paddy soil. The production flux of rice phytolith to sequestrate the atmospheric CO 2 was 46. 55—279. 31 kg hm-2a-1and the accumulation flux of paddy soil phytolith sequestrate the atmospheric CO 2 was 1. 48—8. 88 kg hm-2a-1. It was promising to improve the fluxes of phytolith production and the phytolith to sequestrate CO 2 by selecting high phytolith content rice varities such as Jiahua11.

A 340,000 year continental climate record from tropical Africa – news from opal phytoliths from the equatorial Atlantic

Information on the tropical African continental climate and vegetation during the last 340 kyr is derived from a detailed study of opal phytoliths at the eastern equatorial Atlantic site M16772 (1°21′S, 11°58′W). Total phytoliths as well as C 3 and C 4 grass phytoliths are compared to the distribution pattern of other continental climate proxies (freshwater and limnobiontic diatoms). Total phytolith accumulation rate is dominated by C 4 grasses and their variability confirms the cold stages and interstadials as times of arid conditions in the southern Sahara and Sahel regions, and indicates an increase in aridness from Termination II to Termination I. The good agreement between the total phytoliths and freshwater diatom records observed for most of the 340 kyr is interpreted as indicative of atmospheric dust as the main source of both sediment constituents to this core site. Exceptionally higher land rainfall and river input to the eastern equatorial Atlantic are suggested by the excess of freshwater diatoms over total phytoliths and the limnobiontic diatoms observed during ice growth phases of oxygen isotopic interglacial stages 9, 7 and the 5/4 transition. Major alterations in continental aridity and/or wind strength conditions over north Africa, as reflected by the total and arid phytolith frequency spectrum, appear clearly determined by global ice volume and the 100 kyr cycle characteristic for high-latitude climate change. Limnobiontic diatoms, which reflect lake desiccation, respond also to the 41 kyr obliquity cycle. Freshwater diatoms, on the other hand, contain significant variance at 23 kyr periodicities, reflecting the precessional forcing of the African monsoons which determine the precipitation level over the south Saharan and Sahelian source regions. Rapid hydrological fluctuations, as depicted by the changes in the relative contribution of C 3 and C 4 grasses to the total phytoliths, appear to respond to higher than 19 kyr frequencies, which are observable in all but the aridity index spectra.

PRAIRIE SOIL DEVELOPMENT IN NORTHWESTERN PENNSYLVANIA

Prairies have been noted in several areas of Pennsylvania since the time of European settlement. Because very little is known about the soils of these areas, a prairie area in northwestern Pennsylvania was studied. The A horizon of the soils of this area is thick (mean of 55 cm), and many areas have colors dark enough to qualify as mollic or umbric epipedons. The organic matter content for the top meter of the soils was greater than reported for midwestern prairie soils of similar texture and drainage and probably reflects greater plant growth and/or a lower rate of decomposition as a result of cooler and more moist climatic conditions in northwestern Pennsylvania. The average opal phytolith content for the top 15 cm of the prairie soils was 21.1 Mg ha -1 . The age of these soils, estimated from phytolith accumulation, is 2000 to 6000 years. This would indicate that prairie occupation and soil formation started during the late Hypsithermal (3000 to 7000 years ago) interval. The characteristics of these soils indicate an apparent developmental continuum, extending from the midwest to Pennsylvania, of increasing organic matter accumulation and leaching under prairie vegetation. Although developed under prairie grass, these soils do not meet the base saturation classification requirements of Mollisols and would be classified as Inceptisols (Umbrepts).