Characterization of sp<Superscript>2</Superscript>- and sp<Superscript>3</Superscript>-bonded carbon in wood charcoal

Japanese cedar (Cryptomeria japonica) preheated at 700°C was subsequently heated to 1800°C and characterized by electron microscopy, X-ray diffraction, and micro-Raman spectroscopy. The degree of disorder of carbon crystallites and the amount of amorphous phase decreased considerably with an increase in heat treatment temperature to 1400°C, while carbon crystallites clearly developed above this temperature, showing that the microstructure of carbonized wood undergoes drastic changes around 1400°C. Besides showing the bands for sp²-bonded carbon, the Raman spectra showed a shoulder near 1100 cm⁻¹ assigned to sp³-bonded carbon. With an increase of heat treatment temperature, the peak position of the Raman sp³ band shifted to a lower frequency from 1190 to 1120 cm⁻¹, which is due to the transformation of sp³-bonded carbon from an amorphous phase to a nanocrystalline phase. These data showed that the microstructure of carbonized wood from 700° to 1800°C consisted of the combination of sp²- and sp³-bonded carbon, which is probably due to the disordered microstructure of carbonized wood. It is suggested that the sp³-bonded carbon is transformed from an amorphous structure to a nanocrystalline structure with the growth of polyaromatic stacks at temperatures above 1400°C.     

Tillage effect on C stocks of a clayey Oxisol under a soybean-based crop rotation in the Brazilian Cerrado region

A large area (180 Mha) of central Brazil is occupied by a savanna biome known as the Cerrado. Annual rainfall in this region varies from 1200 to 2000 mm, although there is a long (5 month) dry season with almost no rain. This region is regarded by Brazilians as their agricultural frontier and there is a steady growth in the area dedicated to permanent cropping in the region, which today is estimated to occupy 14 Mha. Owing to the dearth of long-term experiments, the impact of continuous cropping on soil carbon stocks remains unclear. The objective of this study was to evaluate the effects of different tillage systems (zero till (ZT) and conventional tillage (CT)) on the change in soil carbon stocks over a 20-year period of the same crop sequence compared to that under a neighbouring area of native vegetation (NV). Only approximately 10 Mg ha⁻¹ of soil carbon in the 0–100 cm depth interval was lost under continuous ZT. However, under CT systems losses were greater (up to 30 Mg C ha⁻¹) when the mouldboard plough was used and/or tillage was performed twice a year. We did not have access to instrumentation to accurately assess soil charcoal but the C/N data and peroxide and dichromate oxidative techniques suggested that 40% of soil C was in this form. The ¹³C natural abundance of soil profiles indicated that residues of crops (maize) and the spontaneous annual fallow of Brachiaria spp. resulted in integration of significant C₄ residues to a depth of at least 40 cm. It would appear that zero tillage, which is already widely adopted in the Cerrado region of Brazil, will have only a small negative long-term impact on soil C stocks, but ploughing, especially more than once a year, will lead to considerably larger soil C losses.     

Charcoal mineralisation potential of microbial inocula from burned and unburned forest soil with and without substrate addition

Effects of fire on the functioning of the soil microbial community are largely unknown. In this study, we addressed the charcoal mineralisation potential of microbial inocula extracted from burned and unburned soil. The mineralisation of charcoal was analysed during a 1 month incubation experiment under controlled conditions with and without substrate addition. The aim of the study was to elucidate (1) the indirect effect of fire on the functioning of the soil microbial community in terms of charcoal degradation and (2) the possibility to stimulate this degradation by addition of two substrates of increasing complexity. Our conceptual approach included the monitoring of CO₂ emission from microcosms containing laboratory-made charcoal and microbial inocula from burned and unburned soil with and without ¹³C labelled glucose and cellulose.Our results showed higher charcoal mineralisation without substrate addition in microcosms with the inocula from unburned soil compared to burned soil. Charcoal mineralisation was stimulated by the addition of glucose, whereas cellulose addition did not induce a priming effect. We observed a higher stimulation of charcoal mineralisation induced by glucose for the inoculum from burned soil compared to the inoculum from unburned soil. We concluded that fire did affect the functioning of the soil microbial community in terms of charcoal degradation and that the important priming effect induced by glucose may be explained by an increase of the overall microbial activity, rather than selective stimulation of charcoal degrading microbial communities.     

Refinement of shed-microspore culture protocol to increase normal embryos production in hot pepper (Capsicum annuum L.)

A low percentage of normal-looking embryos (20%) is still a problem in an efficient shed-microspore culture of hot pepper (Capsicum annuum L.) and it is more a serious problem in other androgenesic culture systems of pepper. Therefore, several factors were investigated to refine the protocol in order to increase the percentage of normal-looking embryos. The most important factors which improved the protocol and resulted in a significantly higher percentage of normal-looking embryos produces (>50%), were delayed enrichment of the liquid upper layer medium with 2.5 μM Zeatin and 5 μM IAA, and reduced incubation temperature from 28 °C to 21 °C, both after 3 weeks of culture. Addition of 1% activated charcoal in the solid lower layer of the medium enhanced the total embryo yield only, while an application of abscisic acid and increased osmolality medium had a detrimental effect on embryo production. The use of doubled haploid lines as anther donor plants has clearly decreased the variability and improved the statistical analysis of treatment effects. A higher percentage of normal embryos are produced with this refined protocol, and is therefore more suitable for implementation in the breeding programs of hot pepper.     

Black carbon in a temperate mixed-grass savanna

Black carbon (BC) or charcoal is thought to represent an important component of the carbon cycle, but has seldom been quantified in soils. We quantified soil BC in a temperate mixed-grass savanna in the southern Great Plains using benzenecarboxylic acids as molecular markers for BC. Soils were collected from four fire treatments (repeated summer fires in 1992 and 1994; repeated winter fires in 1991, 1993 and 1995; alternate-season fires in winter 1991, summer 1992, and winter 1994; and unburned control) at 0-10 and 10-20 cm depth in 1996. Black carbon concentrations ranged from 50 to 130 g BC kg⁻¹ of soil organic carbon (SOC), or from 0.55 to 1.07 g BC kg⁻¹ of whole soil in this mixed grass savanna. The BC contribution to SOC increased significantly with soil depth (P<0.05). Repeated fires increased BC slightly compared to the unburned controls; however, the effects of repeated fires on BC were not statistically significant in this mixed-grass savanna. Results of this study provide estimates of BC concentrations for native, uncultivated mixed-grass savanna, and indicate that 2-3 fires have little effect on the size of the soil BC pool in this region.     

Biochar mediated alterations in herbicide breakdown and leaching in soil

Biochar application to soil has been proposed as a mechanism for improving soil quality and the long term sequestration of carbon. The implications of biochar on pesticide behavior, particularly in the longer term, however, remains poorly understood. Here we evaluated the influence of biochar type, time after incorporation into soil, dose rate and particle size on the sorption, biodegradation and leaching of the herbicide simazine. We show that typical agronomic application rates of biochar (10-100 t ha⁻¹) led to alterations in soil water herbicide concentrations, availability, transport and spatial heterogeneity. Overall, biochar suppressed simazine biodegradation and reduced simazine leaching. These responses were induced by a rapid and strong sorption of simazine to the biochar which limits its availability to microbial communities. Spatial imaging of ¹⁴C-labeled simazine revealed concentrated hotpsots of herbicide co-localized with biochar in the soil profile. The rate of simazine mineralization, amount of sorption and leaching was inversely correlated with biochar particle size. Biochar aged in the field for 2 years had the same effect as fresh biochar on the sorption and mineralization of simazine, suggesting that the effects of biochar on herbicide behavior may be long lasting. We conclude that biochar application to soil will reduce the dissipation of foliar applied pesticides decreasing the risk of environmental contamination and human exposure via transfer in the food chain, but may affect the efficacy of soil-applied herbicides.     

Biochar effects on soil biota - A review

Soil amendment with biochar is evaluated globally as a means to improve soil fertility and to mitigate climate change. However, the effects of biochar on soil biota have received much less attention than its effects on soil chemical properties. A review of the literature reveals a significant number of early studies on biochar-type materials as soil amendments either for managing pathogens, as inoculant carriers or for manipulative experiments to sorb signaling compounds or toxins. However, no studies exist in the soil biology literature that recognize the observed large variations of biochar physico-chemical properties. This shortcoming has hampered insight into mechanisms by which biochar influences soil microorganisms, fauna and plant roots. Additional factors limiting meaningful interpretation of many datasets are the clearly demonstrated sorption properties that interfere with standard extraction procedures for soil microbial biomass or enzyme assays, and the confounding effects of varying amounts of minerals. In most studies, microbial biomass has been found to increase as a result of biochar additions, with significant changes in microbial community composition and enzyme activities that may explain biogeochemical effects of biochar on element cycles, plant pathogens, and crop growth. Yet, very little is known about the mechanisms through which biochar affects microbial abundance and community composition. The effects of biochar on soil fauna are even less understood than its effects on microorganisms, apart from several notable studies on earthworms. It is clear, however, that sorption phenomena, pH and physical properties of biochars such as pore structure, surface area and mineral matter play important roles in determining how different biochars affect soil biota. Observations on microbial dynamics lead to the conclusion of a possible improved resource use due to co-location of various resources in and around biochars. Sorption and thereby inactivation of growth-inhibiting substances likely plays a role for increased abundance of soil biota. No evidence exists so far for direct negative effects of biochars on plant roots. Occasionally observed decreases in abundance of mycorrhizal fungi are likely caused by concomitant increases in nutrient availability, reducing the need for symbionts. In the short term, the release of a variety of organic molecules from fresh biochar may in some cases be responsible for increases or decreases in abundance and activity of soil biota. A road map for future biochar research must include a systematic appreciation of different biochar-types and basic manipulative experiments that unambiguously identify the interactions between biochar and soil biota.     

Evaluation of Cluster Bean Genotypes for Resistance to Charcoal Rot Caused by Macrophomina phaseolina Using Different Host Inoculation Methods

Abstract

Ten different isolates of Macrophomina phaseolina from cluster bean (Cyamopsis tetragonoloba) selected on the basis of wide geographical distance and potassium chlorate sensitivity, showed remarkable variation in virulence on the susceptible cluster bean genotype, FS 277. Four different host inoculation techniques were employed for resistance screening of six elite cluster bean genotypes under artificial infection conditions using the most pathogenic isolate, MP-6D. The symptoms induced in the plant tissues from seedling to maturity following artificial inoculation clearly simulated lesions produced under natural conditions. Both greenhouse and field experiments demonstrated significant differences in all parameters-plant weight, plant death, root lesion length and stem lesion length-in all the genotypes tested from seedling stage to pod set. The host inoculation methods described in this study might be useful for screening and analysis of crop varieties' resistance to various other disease infestations. The present investigation involved evaluation of pathogenicity of isolates of M. phaseolina as well as a critical examination of occurrence of resistance to charcoal rot in selected cluster bean genotypes. This is the first report on cluster bean resistance to M. phaseolina.     

Forest fires and vegetation during the Holocene in central Yakutia, eastern Siberia

In order to investigate the relationship between vegetation change and fire history in the Siberian boreal forest, fossil pollen and charcoal from two lakes in central Yakutia, eastern Siberia, were analyzed. The vegetation change inferred from the pollen analysis was similar to that found in previous research in the region. Open larch forest covered this region during the late Glacial and early Holocene periods. Later, during the mid-Holocene, Scots pine expanded its range. The low levels of charcoal in the lake deposits represent surface forest fires, suggesting that the present-day surface fire regime has been taking place since at least 6,500 calibrated years before the present (cal yr BP) and that stand-replacing fire has not occurred during the Holocene. Larch and Scots pine forests, which are characterized by surface fire regimes, have been predominant since the early Holocene.     

Molecular mapping of genomic regions harboring QTLs for stalk rot resistance in sorghum

Stalk rot, also called as charcoal rot in India, caused by Macrophomina phaseolina, is an economically important, soil borne disease in major sorghum growing areas across the world. A population of F₉ generation recombinant inbred lines (RILs), derived from IS22380 (susceptible) × E36-1 (resistant), along with parents were phenotyped in sick plots at two locations (Dharwad and Bijapur, Karnataka, India). A total of 85 polymorphic marker loci (62 nuclear and 4 genic SSRs, 19 RAPDs) was available for the construction of genetic map, spanning 650.3 cM in all the ten linkage groups. Analysis with QTL Cartographer (2.5b), adopting composite interval mapping method (LOD > 2.0) at both locations, revealed 5 QTLs at Dharwad and 4 QTLs at Bijapur locations for the component traits of charcoal rot disease resistance. QTLs for number of internodes crossed, length of infection and per cent lodging accounted for 31.83, 10.76 and 18.90 per cent at Dharwad location and 14.87, 10.47 and 26.44 per cent phenotypic variability at Bijapur location, respectively. The QTLs for number of internodes crossed by the rot, length of infection and percent lodging were common across two locations. These QTLs, consistent over environments for the component traits, are likely to assist in marker-assisted selection (MAS) for charcoal rot resistance in sorghum.