Geochronology, Petrogenesis and Oxidation State of the Northparkes Igneous Suite, New South Wales, Australia: Implications for Magma Fertility

2021 ◽  
Author(s):  
Hongda Hao ◽  
Ian H. Campbell ◽  
David R. Cooke ◽  
Eizo Nakamura ◽  
Chie Sakaguchi
Keyword(s):  
Water Content ◽  
Oxidation State ◽  
Geochemical Data ◽  
Island Arcs ◽  
Sulfide Saturation ◽  
Nd Isotope ◽  
Fluid Saturation ◽  
South Wales ◽  
Fluid Release ◽  
Water Contents

Abstract New geochronological and geochemical data for the barren and ore-associated suites from the Northparkes porphyry Cu-Au deposits, Australia, have implications for magma fertility. The Goonumbla and Wombin Volcanics and intrusions are barren in the Northparkes area. A sample from Wombin suite yielded a zircon U-Pb age of 433.8 ± 3.1 Ma, whereas the ore-associated porphyries yielded ages between 441.8 ± 3.7 and 436.3 ± 4.5 Ma. The bulk of the mineralization at Northparkes is associated with a K-feldspar-phyric quartz monzonite porphyry (K-QMP), which gave U-Pb zircon ages of 441.8 ± 3.7 and 441.1 ± 2.5 Ma. Whole-rock Sr-Nd isotope compositions of the Goonumbla, Wombin, and ore-associated suites are similar, with (87Sr/86Sr)i = 0.704112 to 0.704424 and εNd = 5.6 to 6.9, which is typical of primitive intraoceanic island arcs, and their Pb isotope values lie within the MORB array. Most of the zircons from the Wombin and ore-associated suites have arc mantle-like O-Hf isotope compositions, with δ18O values that vary from 6.13 to 4.95, and εHf(t) from 11.5 to 6. These results suggest that the Goonumbla, Wombin, and ore-associated suites originated from typical arc mantle. The magmas that produced the Goonumbla and Wombin suites were dominated by plagioclase-pyroxene fractionation, and the Wombin suite has a low oxidation state with ΔFMQ between ~0 and 1.5. They were relatively reduced and dry. This combination resulted in early sulfide saturation, probably without reaching fluid saturation. Trace element modeling shows that plagioclase-amphibole dominated the later stages of fractionation of the ore-associated suite, implying that it had a higher water content than the barren suites. It was also more oxidized (ΔFMQ from ~0 to 4). The result was late sulfide saturation, which was followed shortly thereafter by voluminous fluid release. As a consequence, the ore-forming fluid effectively transferred Cu and Au from the magma to the site of hydrothermal ore deposition. We suggest that the higher water content and oxidation state of the ore-associated suite was due to the deep underlying magma chamber, which was recharged by many more pulses of magma than the chamber that underlay the barren suites. This is more effective in raising the concentration of incompatible water and ferric iron in the residual melt than straight fractional crystallization. High oxygen fugacities and water contents played a significant role in determining the timing of sulfide and fluid saturation, respectively, and as a result, they had a critical influence on magma fertility.

The Ludicovian of the Raahe–Ladoga Zone of the Fennoscandian Shield (Isotope-Geochemical Composition and Geodynamic Nature)

2021 ◽  
Vol 62 (10) ◽  
pp. 1089-1106
Author(s):  
A.B. Vrevskii
Keyword(s):  
Isotope Composition ◽  
Geochemical Data ◽  
Island Arcs ◽  
Karelian Craton ◽  
Geochemical Composition ◽  
Nd Isotope ◽  
Tectonic Model ◽  
Isotope System ◽  
Nd Isotope Composition

Abstract —In the northern Ladoga area, the age of the Sortavala Group rocks in the southeast of the Raahe–Ladoga zone of junction of the epi-Archean Fenno-Karelian Craton and the Paleoproterozoic Svecofennian province, their relationship with dome granitoids, the age of the provenances, and the time of metamorphic processes were estimated. The study was focused on the Nd isotope composition of rocks, the geochemical and isotope-geochronological parameters of zircon from the granite-gneisses of the Kirjavalakhti dome, the basal graywackes of the lower unit and the trachytes of the middle unit of the Sortavala Group, and the plagio- and diorite-porphyry dikes cutting the volcanosedimentary units of this group. The new isotope-geochemical data show a Neoarchean age of the granitoids of the Kirjavalakhti dome (2695 ± 13 Ma) and their juvenile nature (εNd(T) = +1.5). The granitoids underwent tectonometamorphic transformations (rheomorphism) in the Paleoproterozoic (Sumian) (2.50–2.45 Ga), which are recorded in the U–Th–Pb isotope system of the rims of the ancient cores of zircon crystals. The volcanosedimentary complex of the Sortavala Group formed on the heterogeneous polychronous (3.10–2.46 Ga) continental crust of the epi-Archean Fenno-Karelian Craton. With regard to the errors in determination of the age of clastic zircon, the minimum concordant U–Th–Pb ages of 1940–1990 Ma of detrital zircon from volcanomictic graywackes of the Pitkyaranta Formation can be taken as the upper age bound of terrigenous rocks, which agrees with the maximum age of the Sortavala Group rocks estimated from the U–Th–Pb (SIMS) age of 1922 ± 11 Ma of the Tervaoya diorites (Matrenichev et al., 2006). According to the proposed new tectonic model, the accumulation of the volcanosedimentary complex of the Sortavala Group, its metamorphism, erosion, and overlapping by the Ladoga Group turbidites had already occurred in the pericratonic part of the epi-Archean Fenno-Karelian Craton by the time of the Svecofennian continent–island arc collision, subduction, and formation of bimodal volcanoplutonic complexes of the young Pyhäsalmi island arcs and felsic volcanics of the Savo schist belt (1920–1890 Ma).

MITIGATION YIELD SCALED METHANE EMISSION FROM RICE GROWN IN WATER STRESS CONDITIONS WITH BIOCHAR AND SILICATE AMENDMENTS

2021 ◽  
Author(s):  
MUHAMMAD ASLAM ALI ◽  
SANJIT CHANDRA BARMAN ◽  
MD. ASHRAFUL ISLAM KHAN ◽  
MD. BADIUZZAMAN KHAN ◽  
HAFSA JAHAN HIYA
Keyword(s):  
Water Stress ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Field Capacity ◽  
Saturated Soil ◽  
Rice Grain ◽  
Standing Water ◽  
Water Contents ◽  
Soil Water Contents

Climate change and water scarcity may badly affect existing rice production system in Bangladesh. With a view to sustain rice productivity and mitigate yield scaled CH4 emission in the changing climatic conditions, a pot experiment was conducted under different soil water contents, biochar and silicate amendments with inorganic fertilization (NPKS). In this regard, 12 treatments combinations of biochar, silicate and NPKS fertilizer along with continuous standing water (CSW), soil saturation water content and field capacity (100% and 50%) moisture levels were arranged into rice planted potted soils. Gas samples were collected from rice planted pots through Closed Chamber technique and analyzed by Gas Chromatograph. This study revealed that seasonal CH4 emissions were suppressed through integrated biochar and silicate amendments with NPKS fertilizer (50–75% of the recommended doze), while increased rice yield significantly at different soil water contents. Biochar and silicate amendments with NPKS fertilizer (50% of the recommended doze) increased rice grain yield by 10.9%, 18.1%, 13.0% and 14.2%, while decreased seasonal CH4 emissions by 22.8%, 20.9%, 23.3% and 24.3% at continuous standing water level (CSW) (T9), at saturated soil water content (T10), at 100% field capacity soil water content (T11) and at 50% field capacity soil water content (T12), respectively. Soil porosity, soil redox status, SOC and free iron oxide contents were improved with biochar and silicate amendments. Furthermore, rice root oxidation activity (ROA) was found more dominant in water stress condition compared to flooded and saturated soil water contents, which ultimately reduced seasonal CH4 emissions as well as yield scaled CH4 emission. Conclusively, soil amendments with biochar and silicate fertilizer may be a rational practice to reduce the demand for inorganic fertilization and mitigate CH4 emissions during rice cultivation under water stress drought conditions.

scholarly journals Effect of Nano-Carbon on Water Holding Capacity in a Sandy Soil of the Loess Plateau

2017 ◽  
Vol 21 (4) ◽  
pp. 189-195 ◽  
Author(s):  
Beibei Zhou ◽  
Xiaopeng Chen
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Loess Plateau ◽  
Sandy Soil ◽  
Water Retention ◽  
Soil Mixture ◽  
Cumulative Infiltration ◽  
Nano Carbon ◽  
Water Contents ◽  
Soil Water Contents

The poor water retention capacity of sandy soils commonly aggregate soil erosion and ecological environment on the Chinese Loess Plateau. Due to its strong capacity for absorption and large specific surface area, the use of nanocarbon made of coconut shell as a soil amendment that could improve water retention was investigated. Soil column experiments were conducted in which a layer of nanocarbon mixed well with the soil was formed at a depth of 20 cm below the soil surface. Four different nanocarbon contents by weight (0%, 0.1%, 0.5%, and 1%) and five thicknesses of the nanocarbon- soil mixture layer ranging from 1 to 5 cm were considered. Cumulative infiltration and soil water content distributions were determined when water was added to soil columns. Soil Water Characteristic Curves (SWCC) were obtained using the centrifuge method. The principal results showed that the infiltration rate and cumulative infiltration increased with the increases of nanocarbon contents, to the thicknesses of the nano carbon-soil mixture layer. Soil water contents that below the soil-nano carbon layer decreased sharply. Both the Brooks-Corey and van Genuchten models could describe well the SWCC of the disturbed sandy soil with various nano carbon contents. Both the saturated water content (θs), residual water content (θr) and empirical parameter (α) increased with increasing nano carbon content, while the pore-size distribution parameter (n) decreased. The available soil water contents were efficiently increased with the increase in nanocarbon contents.

Origin of the Ordovician Mansehra granite in the NW Himalaya, Pakistan: constraints from Sr–Nd isotopic data, zircon U–Pb age and Hf isotopes

2018 ◽  
Vol 481 (1) ◽  
pp. 277-298 ◽  
Author(s):  
Masatsugu Ogasawara ◽  
Mayuko Fukuyama ◽  
Rehanul Haq Siddiqui ◽  
Ye Zhao
Keyword(s):  
Granitic Magma ◽  
Geochemical Data ◽  
Large Contribution ◽  
Crustal Material ◽  
Sr Isotope ◽  
Nw Himalaya ◽  
Nd Isotope ◽  
Isotope Data ◽  
Late Neoproterozoic ◽  
T Values

AbstractThe Mansehra granite in the NW Himalaya is a typical Lesser Himalayan granite. We present here new whole-rock geochemistry, Rb–Sr and Sm–Nd isotope data, together with zircon U–Pb ages and Hf isotope data, for the Mansehra granite. Geochemical data for the granite show typical S-type characteristics. Zircon U–Pb dating yields 206Pb/238U crystallization ages of 483–476 Ma. The zircon grains contain abundant inherited cores and some of these show a clear detrital origin. The 206Pb/238U ages of the inherited cores in the granite cluster in the ranges 889–664, 1862–1595 and 2029 Ma. An age of 664 Ma is considered to be the maximum age of the sedimentary protoliths. Thus the Late Neoproterozoic to Cambrian sedimentary rocks must be the protolith of the Mansehra granitic magma. The initial Sr isotope ratios are high, ranging from 0.7324 to 0.7444, whereas the εNd(t) values range from −9.2 to −8.6, which strongly suggests a large contribution of old crustal material to the protoliths. The two-stage Nd model ages and zircon Hf model ages are Paleoproterozoic, indicating that the protolith sediments were derived from Paleoproterozoic crustal components.

scholarly journals Synchrotron FTIR imaging of OH in quartz mylonites

Solid Earth ◽  
2017 ◽  
Vol 8 (5) ◽  
pp. 1025-1045 ◽  
Author(s):  
Andreas K. Kronenberg ◽  
Hasnor F. B. Hasnan ◽  
Caleb W. Holyoke III ◽  
Richard D. Law ◽  
Zhenxian Liu ◽  
...  
Keyword(s):  
Water Content ◽  
Point Defects ◽  
Fluid Inclusions ◽  
Hanging Wall ◽  
Molecular Water ◽  
Main Central Thrust ◽  
Absorption Bands ◽  
Uniform Equilibrium ◽  
Quartz Grains ◽  
Water Contents

Abstract. Previous measurements of water in deformed quartzites using conventional Fourier transform infrared spectroscopy (FTIR) instruments have shown that water contents of larger grains vary from one grain to another. However, the non-equilibrium variations in water content between neighboring grains and within quartz grains cannot be interrogated further without greater measurement resolution, nor can water contents be measured in finely recrystallized grains without including absorption bands due to fluid inclusions, films, and secondary minerals at grain boundaries.Synchrotron infrared (IR) radiation coupled to a FTIR spectrometer has allowed us to distinguish and measure OH bands due to fluid inclusions, hydrogen point defects, and secondary hydrous mineral inclusions through an aperture of 10 µm for specimens > 40 µm thick. Doubly polished infrared (IR) plates can be prepared with thicknesses down to 4–8 µm, but measurement of small OH bands is currently limited by strong interference fringes for samples < 25 µm thick, precluding measurements of water within individual, finely recrystallized grains. By translating specimens under the 10 µm IR beam by steps of 10 to 50 µm, using a software-controlled x − y stage, spectra have been collected over specimen areas of nearly 4.5 mm2. This technique allowed us to separate and quantify broad OH bands due to fluid inclusions in quartz and OH bands due to micas and map their distributions in quartzites from the Moine Thrust (Scotland) and Main Central Thrust (Himalayas).Mylonitic quartzites deformed under greenschist facies conditions in the footwall to the Moine Thrust (MT) exhibit a large and variable 3400 cm−1 OH absorption band due to molecular water, and maps of water content corresponding to fluid inclusions show that inclusion densities correlate with deformation and recrystallization microstructures. Quartz grains of mylonitic orthogneisses and paragneisses deformed under amphibolite conditions in the hanging wall to the Main Central Thrust (MCT) exhibit smaller broad OH bands, and spectra are dominated by sharp bands at 3595 to 3379 cm−1 due to hydrogen point defects that appear to have uniform, equilibrium concentrations in the driest samples. The broad OH band at 3400 cm−1 in these rocks is much less common. The variable water concentrations of MT quartzites and lack of detectable water in highly sheared MCT mylonites challenge our understanding of quartz rheology. However, where water absorption bands can be detected and compared with deformation microstructures, OH concentration maps provide information on the histories of deformation and recovery, evidence for the introduction and loss of fluid inclusions, and water weakening processes.

Effects of differential drying rates on viability retention of recalcitrant seeds of Ekebergia capensis

1998 ◽  
Vol 8 (4) ◽  
pp. 463-471 ◽  
Author(s):  
N. W. Pammenter ◽  
Valerie Greggains ◽  
J. I. Kioko ◽  
J. Wesley-Smith ◽  
Patricia Berjak ◽  
...  
Keyword(s):  
Water Content ◽  
Exponential Function ◽  
Time Course ◽  
Drying Rate ◽  
Recalcitrant Seeds ◽  
Tissue Water ◽  
Initial Water ◽  
Viability Loss ◽  
Drying Rates ◽  
Water Contents

AbstractThe drying rate of whole seeds of Ekebergia capensis (Meliaceae) was shown to influence the response to desiccation, with rapidly dried seeds surviving to lower water contents. Short-term rapid drying (to water contents higher than those leading to viability loss) actually increased the rate of germination. The form of the time course of decline of axis water content varied with drying rate; slow drying could be described by an exponential function, whereas with rapid drying initial water loss was faster than predicted by an exponential function. These observations suggest that slow drying brought about homogeneous dehydration and that the rapid drying was uneven across the tissue. This raised the possibility that the different responses to dehydration were a function of different distributions of water in the axis tissue under the two drying regimes. However, ultrastructural observations indicated that different deleterious processes may be occurring under the different drying treatments. It was tentatively concluded that a major cause of viability loss in slowly dried material was likely to be a consequence of aqueous-based processes leading to considerable membrane degradation. Uneven distribution of tissue water could not be rejected as a contributory cause of the survival of rapidly dried seeds to low bulk water contents. The differential response to dehydration at different drying rates implies that it is not possible to determine a ‘critical water content’ for viability loss by recalcitrant seeds.

scholarly journals An empirical model for describing the influence of water content and concentration of sulfamethoxazole (antibiotic) in soil on the total net CO2 efflux

2020 ◽  
Vol 68 (4) ◽  
pp. 351-358
Author(s):  
Miroslav Fér ◽  
Radka Kodešová ◽  
Barbora Kalkušová ◽  
Aleš Klement ◽  
Antonín Nikodem
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Solution Treatment ◽  
Soil Microbial Activity ◽  
Soil Samples ◽  
Co2 Efflux ◽  
The Impact ◽  
Water Contents ◽  
Soil Water Contents

AbstractThe aim of the study was to describe the impact of the soil water content and sulfamethoxazole, SUL, (antibiotic) concentration in soil on the net CO2 efflux. Soil samples were taken from topsoils of a Haplic Fluvisol and Haplic Chernozem. Soil samples were packed into the steel cylinders. The net CO2 efflux was measured from these soil columns after application of fresh water or SUL solution at different soil water contents. The experiments were carried out in dark at 20°C. The trends in the net CO2 efflux varied for different treatments. While initially high values for water treatment exponentially decreased in time, values for solution treatment increased during the first 250–650 minutes and then decreased. The total net CO2 effluxes measured for 20 hours related to the soil water content followed the second order polynomial functions. The maximal values were measured for the soil water content of 0.15 cm3 cm−3 (Haplic Fluvisol with water or solution, Haplic Chernozem with solution) and 0.11 cm3 cm−3 (Haplic Chernozem with water). The ratios between values measured for solution and water at the same soil water contents exponentially increased with increasing SUL concentration in soils. This proved the increasing stimulative influence of SUL on soil microbial activity.

scholarly journals REGRESSÃO QUADRÁTICA PARA TEORES DE ÁGUA EM FUNÇÃO DA COMPACTAÇÃO DO SOLO

Irriga ◽  
2021 ◽  
Vol 26 (1) ◽  
pp. 186-194
Author(s):  
Barbara Barreto Fernandes ◽  
Indiamara Marasca ◽  
Murilo Battistuzzi Martins ◽  
Jefferson Sandi ◽  
Kleber Pereira Lanças
Keyword(s):  
Water Content ◽  
Clayey Soil ◽  
Superficial Layer ◽  
Mechanical Resistance ◽  
Mato Grosso ◽  
Randomized Design ◽  
Influence Of Water ◽  
E Mail ◽  
Mato Grosso Do Sul ◽  
Water Contents

REGRESSÃO QUADRÁTICA PARA TEORES DE ÁGUA EM FUNÇÃO DA COMPACTAÇÃO DO SOLO     Barbara Barreto Fernandes¹; Indiamara Marasca²; Murilo³ Battistuzzi Martins; Jefferson Sandi4 e Kleber Pereira Lanças5   1 Engenheira agrônoma, Rua Luis Carlos Da Silveira, 345, Tenis Clube, 19806-370, Assis – SP, Brasil. E-mail: [email protected] 2 Engenheira agrônoma, Fazenda Cachoeira do Montividiu – 75915-000, Montividiu – GO, Brasil. E-mail: [email protected] 3 Universidade Estadual de Mato Grosso do Sul – Unidade de Cassilândia. Rodovia MS 306 - km 6,4; 79540-000, Cassilândia, MS, Brasil. E-mail:  [email protected] 4 Universidade La Salle de Lucas do Rio Verde. Av. Universitária, 1000, Parque das Emas - 78455-000, Lucas do Rio Verde, MT, Brasil. E-mail: [email protected] 5 Departamento de Engenharia Rural na FCA/UNESP, Av. Universitária, 3780 - Altos do Paraíso, 18610-034, Botucatu, SP, Brasil. E-mail: [email protected]     1 RESUMO   O trabalho teve por objetivo avaliar a influência do teor de água na avaliação de resistência mecânica a penetração do solo, medida através do índice de cone. O experimento foi realizado na UNESP/FCA, Botucatu-SP, sendo selecionadas duas classes de solo: o Nitossolo Vermelho distroférrico e o Latossolo Vermelho. Utilizou-se o delineamento inteiramente casualizado, com os seguintes tratamentos de compactação: T0 = 0; T1 = 1; T2 = 2; T3 = 3; T4=5 e T5 = 10 passadas consecutivas de um trator agrícola. Utilizou-se um penetrômetro hidráulico-eletrônico para a amostragem da resistência mecânica do solo à penetração nas camadas de: 0,00 - 0,10; 0,10 - 0,20; 0,20 - 0,30; 0,30 - 0,40 m em quatro condições de teor de água. Com o aumento do tráfego, maior foi a compactação. Porém para o solo argiloso, a partir de uma passada do trator, os valores de resistência à penetração tiveram pouco aumento, não diferindo estatisticamente para a camada mais superficial (0-0,20 m) e para a camada de 0,20-0,40 m a partir de duas passadas. Para o solo de textura média, este comportamento foi observado a partir de uma passada para a camada mais superficial (0-0,20 m) e de cinco passadas para a camada de 0,20-0,40m.   Palavras-chave: resistência do solo, umidade, agregação.     FERNANDES, B. B.; MARASCA, I.; MARTINS, M. B.; SANDI, J.; LANÇAS, K. P. QUADRACTIC REGRESSION FOR WATER CONTENTS IN THE FUNCTION OF SOIL COMPACTION     2 ABSTRACT   The objective of this work was to evaluate the influence of water content in the evaluation of mechanical resistance to soil penetration, measured through the cone index. The experiment was conducted at UNESP/FCA, Botucatu - SP, being selected two classes of soil: a Nitossolo Vermelho distroférrico and a Latosolo Vermelho. A completely randomized design was used, with the following compaction treatments: T0 = 0; T1 = 1; T2 = 2; T3 = 3; T4 = 5 and T5 = 10 consecutive passes of an agricultural tractor. A hydraulic-electronic penetrometer was used to sample the mechanical resistance of the soil to penetrate the layers; 0.00 – 0.10; 0.10 - 0.20; 0.20 - 0.30; 0.30 - 0.40 m in four water content conditions. With the increase in traffic, greater was the compression. However, for the clayey soil, from a tractor pass, the penetration resistance values ​​had a small increase, not differing statistically for the most superficial layer (0 - 0.20m) and for the 0.20 - 0.40 m layer from two passes. For medium textured soil, this behavior was observed from one pass to the most superficial layer (0 - 0.20 m) and five passes to the 0.20 - 0.40 m layer.   Keywords: soil resistance; moisture; aggregation.      

Influence of Water Content of Soil to Strength of Unfired Soil Lime Bricks

2015 ◽  
Vol 719-720 ◽  
pp. 187-192
Author(s):  
Heru Purnomo ◽  
Rahmat N.D. Syah ◽  
Mochammad R. Syaifulloh ◽  
Srikandi W. Arini ◽  
Essy Arijoeni Basoenondo ◽  
...  
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Modulus Of Rupture ◽  
Bending Test ◽  
Physical Change ◽  
Three Point Bending ◽  
Mass Proportion ◽  
Influence Of Water ◽  
Water Contents

The paper discusses strength-time relation of unfired soil-lime bricks in presence of different water content of soil as one of principal materials for the brick making. Two batches of soil-lime bricks were made with a mixture of lime, soil and water with a mass proportion of 1: 5.7: 1. Water contents of the first and second batch of soil are 30% and 40.581% respectively. Both batches of brick underwent compression and three point bending test. Absorption and physical change of bricks were also evaluated. Experimental investigation reveals that for both batches of bricks, up to 90 days compressive strength decreases a little but modulus of rupture rapidly decreases with time. The study shows that unfired soil-lime bricks with lower soil water content resulted in better strength performances compared to those with higher soil water content.

Desiccation sensitivity and activities of free radical-scavenging enzymes in recalcitrant Theobroma cacao seeds

1999 ◽  
Vol 9 (3) ◽  
pp. 209-217 ◽  
Author(s):  
Changrun Li ◽  
Wendell Q. Sun
Keyword(s):  
Lipid Peroxidation ◽  
Superoxide Dismutase ◽  
Water Content ◽  
Theobroma Cacao ◽  
Radical Scavenging ◽  
Free Radical Scavenging ◽  
Desiccation Sensitivity ◽  
Critical Water Content ◽  
Scavenging Enzymes ◽  
Water Contents

AbstractMature and immature axes of Theobroma cacao (cocoa) seeds tolerated desiccation under a rapid-drying regime to critical water contents of 1.0 and 1.7 g g-1 dw, respectively. These critical water contents corresponded to water contents below which activities of free radical-scavenging enzymes (ascorbate peroxidase, peroxidase and superoxide dismutase) decreased rapidly during desiccation. The decline in axis viability below the critical water content was correlated with sharp increases in lipid peroxidation and cellular leakage. Cotyledon tissues were more desiccation-tolerant than axes, with a low critical water content of 0.24 g g–1dw. Desiccation sensitivity in cotyledon tissues was also correlated with the decrease in superoxide dismutase activity and increased lipid peroxidation products. However, in the cotyledons, no ascorbate peroxidase activity was detected at any water content, and peroxidase activity was gradually reduced as desiccation proceeded. Cocoa embryonic axes contained large amounts of sucrose, raffinose and stachyose but only traces of reducing monosaccharides. Desiccation sensitivity of recalcitrant cocoa axes did not appear to be due to the lack of sugar-related protective mechanisms during desiccation, and it was more likely related to the decrease of enzymic protection against desiccation-induced oxidative stresses.

Sign in / Sign up

Export Citation Format

Share Document