Jeffrey F Parr

13C-depleted charcoal from C4 grasses and the role of occluded carbon in phytoliths

The δ13C values of plants and corresponding charred materials from wood, C3 and C4 grasses, derived from natural burning and laboratory combustion were obtained to determine whether there was a significant difference in δ13C of grass-derived char (C3 and C4) compared with wood-derived (C3) char. Our data showed that there is an up to 8‰ 13C-depletion in C4-derived chars from natural burning but there was no significant isotopic change in chars from wood or C3 grasses. We suggest that this 13C-depletion in C4-derived chars is due to protected organic matter in silicate structures (phytoliths), which were found to be depleted by up to 9‰. Analysis of this protected carbon by Py-GCMS indicated the presence of low relative amounts of n-alkanes. However, 13C-NMR data suggested that a significant portion of the phytolith-occluded material was composed of simple carbohydrates (O-alkyl carbon) and that alkyl carbon (lipid material) constituted a minor fraction. These isotopic and spectroscopic data have important implications for the calculation of the proportions of C3- versus C4-derived charred organic matter in modern as well as geological studies.

A microwave digestion method for the extraction of phytoliths from herbarium specimens

Abstract The extraction of phytoliths from herbarium and/or fresh plant material to obtain a suite of comparative reference samples is an essential component of palaeobotanical studies for the accurate interpretation of fossil phytolith assemblages. A number of established methods have been employed to extract phytoliths from plant material including dry ashing and acid digestion. However, while these methods produce good results, they can be time consuming and have the potential to produce results with some cross-contamination if not monitored closely. In this study, we trial an alternative method using microwave digestion, and compare the results to those produced using a conventional dry ashing method. The results of this study indicate that the microwave digestion technique is quick, eliminates concerns of cross-contamination and produces comparable phytolith assemblages to those of the conventional dry ashing method.

A comparison of heavy liquid floatation and microwave digestion techniques for the extraction of fossil phytoliths from sediments

Abstract This paper reports the results of a comparative analysis of two techniques used for the extraction of fossil phytoliths from sediments. The first is a standard heavy liquid floatation extraction technique that has been successfully used and proven to provide reliable phytolith assemblage data. A second technique using a Perkin-Elmer Multiwave Microwave Sample Preparation System is introduced, and the results are compared to those of the conventional technique. Results for both techniques, as well as the advantages and disadvantages of their use are discussed. This study provides an introduction to an alternative technique for the extraction of fossil phytoliths and possibly starch grains from sediments. The microwave technique is fast, inexpensive, omits the need for heavy liquid floatation and most importantly results in the appropriation of interpretable and replicable fossil phytolith assemblage data.

Sugarcane phytoliths: Encapsulation and sequestration of a long-lived carbon fraction

The potential to reduce emissions from agriculture and increase the amount of carbon captured in soils is currently being examined by researchers in a number of countries. This paper describes a process of carbon capture and long-term storage using silica phytoliths and, provides the results of a study of this process on newly planted and ratooned sugarcane varieties. Our results indicate that a) there was significant variation in the phytolith occluded carbon (PhytOC) content of different varieties, b) this did not appear to be directly related to the quantity of silica in the plant but rather the efficiency of carbon encapsulation by individual varieties and c) it was possible to accurately quantify this carbon fraction prior to its incorporation into soil. The carbon content of the varieties tested under the particular suite of environmental conditions for which they were grown ranged from 0.12 te-CO2 ha-y−1 to 0.36 te-CO2 ha-y−1. This PhytOC process provides an approach which reduces emissions from agriculture for the long-term (millennia), as opposed to many other soil organic carbon fractions that may decompose over a much shorter time. Moreover, the ability to quantify PhytOC prior to its incorporation into the soil will provide a distinct practical advantage for the quantification of this carbon form over other soil carbon fractions in emerging emissions trading and offset markets.

Raman, infrared and XPS study of bamboo phytoliths after chemical digestion

Raman, infrared and X-ray photoelectron spectroscopies have been used to examine the effect of various chemical digestion methods on the composition of bamboo phytoliths. Intact bilobate phytoliths, suitable for interrogation by Raman microprobe analysis, were isolated by a microwave wet ashing technique using hydrogen peroxide with nitric and hydrochloric acids. The occluded phytolith carbon presented evidence of cellulose, lignin and carboxylic acids. Nitrate from the nitric acid used in the digestion was observed in homogenized samples of the isolated phytoliths; in addition to nitrogen of plant origin occluded within the phytolith, which was observed as amine nitrogen and ammonia. Intact bilobate phytoliths were not observed following an exothermic hydrogen peroxide/sulfuric acid digest, suggesting that these structures ruptured during this digestion procedure. The silicate network was significantly altered during isolation using the exothermic hydrogen peroxide/sulfuric digest, with surface hydroxyls undergoing condensation to form a SiO(3) ring structure.

Comparison of two methods for the isolation of phytolith occluded carbon from plant material

Background and aimsPhytolith occluded carbon (PhytOC) is of interest for isotope studies, dating of sediments and the capture and storage of carbon. Many methodologies have been used for the isolation of phytoliths from plant material; however, there are wide disparities in the PhytOC contents when determined by different methodologies. In this study we examine the utility of the two main methods used for quantifying PhytOC.MethodsThese methods are: (1) a microwave digestion followed by a Walkley-Black digestion, and (2) H2SO4/H2O2.ResultsMethod (1) produced PhytOC values over 50 times higher than those acquired by method (2). SEM examination indicated that the differences were likely due to shattering of the phytoliths by method (2) allowing consumption by the acid and peroxide of PhytOC .ConclusionThese results indicate that for the samples analysed here: 1] the modified microwave method allowed the total PhytOC to be measured, 2] the H2SO4/H2O2 method allowed the PhytOC within the tightly packed silica matrix to be measured, and 3] the PhytOC retained within the phytolith cavities could possibly be calculated by subtracting 2] from 1]. For the samples analysed here most of the PhytOC resided in the phytolith cavities.

Potential of global cropland phytolith carbon sink from optimization of cropping system and fertilization.

The occlusion of carbon (C) by phytoliths, the recalcitrant silicified structures deposited within plant tissues, is an important persistent C sink mechanism for croplands and other grass-dominated ecosystems. By constructing a silica content-phytolith content transfer function and calculating the magnitude of phytolith C sink in global croplands with relevant crop production data, this study investigated the present and potential of phytolith C sinks in global croplands and its contribution to the cropland C balance to understand the cropland C cycle and enhance long-term C sequestration in croplands. Our results indicate that the phytolith sink annually sequesters 26.35±10.22 Tg of carbon dioxide (CO2) and may contribute 40±18% of the global net cropland soil C sink for 1961–2100. Rice (25%), wheat (19%) and maize (23%) are the dominant contributing crop species to this phytolith C sink. Continentally, the main contributors are Asia (49%), North America (17%) and Europe (16%). The sink has tripled since 1961, mainly due to fertilizer application and irrigation. Cropland phytolith C sinks may be further enhanced by adopting cropland management practices such as optimization of cropping system and fertilization.

Diatom community response to climate variability over the past 37,000 years in the sub-tropics of the Southern Hemisphere.

Climate change is impacting global surface water resources, increasing the need for a deeper understanding of the interaction between climate and biological diversity. This is particularly the case in the Southern Hemisphere sub-tropics, where little information exists on the aquatic biota response to climate variations. Palaeolimnological techniques, in particular the use of diatoms, are well established and can significantly contribute to the understanding of climatic variability and the impacts that change in climate have on aquatic ecosystems. A sediment core from Lake McKenzie, Fraser Island (Australia), was used to investigate interactions between climate influences and aquatic ecosystems. This study utilises a combination of proxies including biological (diatom), geochemical and chronological techniques to investigate long-term aquatic changes within the perched-dune lake. A combination of (210)Pb and AMS (14)C dates showed that the retrieved sediment represented a history of ca. 37,000 cal.yBP. The sedimentation rate in Lake McKenzie is very low, ranging on average from 0.11 mm to 0.26 mm per year. A sediment hiatus was observed between ca. 18,300 and 14,000 cal.yBP suggesting a period of dry conditions at the site. The diatom record shows little variability over the period of record, with benthic, freshwater acidic tolerant species dominating. Relative abundance of planktonic species and geochemical results indicates a period of increased water depth and lake productivity in the early Holocene and a gradual decrease in effective precipitation throughout the Holocene. Results from this study not only support earlier work conducted on Fraser Island using pollen reconstructions but also demonstrate that diatom community diversity has been relatively consistent throughout the Holocene and late Pleistocene with only minor cyclical fluctuation evident. This record is consistent with the few other aquatic palaeoecological records from the Southern Hemisphere sub-tropics.

Once, twice maybe, but not three times: Reheating Xanthorrhoea australis resin

Hafting is a process in which a handle is attached to a stone tool adding to its functionability and/or ease of use. This was normally achieved by using a resinous plant exudate as a fixative (Flood 1995:270) which was heated and then fashioned into place (Cribb and Cribb 1982:89). The resin may also have been reinforced with other materials such as grass, beeswax and fine sand (Cribb and Cribb 1982:89).

Implications of phytolith and diatom assemblages in the cultural layers of prehistoric archaeological sites of Ban Non Wat and Nong Hua Raet in Northeast Thailand

The Mun River valley is an imortant prehistoric archaeological region in Northeast Thailand and represents a rich and long period of occupation spanning two millennia during the Neolithic, Bronze and Iron ages. Extensive archaeological investigation provides a rich picture of the day-to-day life of the inhabitants of the many sites scattered throughout the region.