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71.
REYNALDO LUIZ VICTORIA FERNANDO FERNANDES† LUIZ ANTONIO MARTINELLI MARISA DE CÁSSIA PICCOLO PLINIO BARBOSA DE CAMARGO SUSAN TRUMBORE‡ 《Global Change Biology》1995,1(3):165-171
Measurements of the organic carbon inventory, its stable isotopic composition and radiocarbon content were used to deduce vegetation history from two soil profiles in arboreal and grassy savanna ecotones in the Brazilian Pantanal. The Pantanal is a large floodplain area with grass-dominated lowlands subject to seasonal flooding, and arboreal savanna uplands which are only rarely flooded. Organic carbon inventories were lower in the grassy savanna site than in the upland arboreal savanna site, with carbon decreasing exponentially with depth from the surface in both profiles. Changes in 13C of soil organic matter (SOM) with depth differed markedly between the two sites. Differences in surface SOM 13C values reflect the change from C3 to C4 plants between the sites, as confirmed by measurements of 13C of vegetation and the soil surface along a transect between the upland closed-canopy forest and lowland grassy savanna. Changes of 13C in SOM with depth at both sites are larger than the 3–4 per mil increases expected from fractionation associated with organic matter decomposition. We interpret these as recording past changes in the relative abundance of C3 and C4 plants at these sites. Mass balances with 14C and 13C suggest that past vegetational changes from C3 to C4 plants in the grassy savanna, and in the deeper part of the arboreal savanna, occurred between 4600 and 11 400 BP, when major climatic changes were also observed in several places of the South American Continent. The change from C4 to C3, observed only in the upper part of the arboreal savanna, was much more recent (1400 BP), and was probably caused by a local change in the flooding regime. 相似文献
72.
The distribution and abundance of Thelypteris limbosperma, Athyrium distentifolium, and Matteuccia struthiopteris are modelled statistically in relation to 14 environmental variables along the major climatic, topographic, and edaphic gradients in western Norway. The data are from 624 stands from which measurements or estimates of mean January and mean July temperatures, humidity, altitude, aspect, and slope are available. From 182 of these stands eight soil variables have also been measured. The species responses are quantified by two numerical methods: Gaussian logit regression and weighted averaging (WA) regression. The estimated WA optima suggest that A. distentifolium has an ecological preference for low July and January temperatures, high altitudes, and soils of low-medium pH and base content. The species shows statistically significant Gaussian responses with summer temperature, humidity (= Martonnes humidity index), altitude, slope, aspect, pH, cation exchange capacity, and base saturation with optima of 8.7 °C, 188.9, 1220 m, 28°, 29°, 4.8, 13.77 mEq 100 g dry soil-1, and 13.4%, respectively. These suggest that the occurrence and relative abundance of A. distentifolium are well predicted by summer temperature, topography, and soil pH and base status. T. limbosperma has WA optima that suggest that it favours moderately high winter and summer temperatures, high humidity, medium altitude, and soils of low pH and base content. It has significant Gaussian responses to summer temperature (optimum =12.6 °C), winter temperature (-1.8 °C), humidity (179.2), altitude (459.5 m), slope (22.5°), and Na (0.7 mg 100 g dry soil-1). These suggest that climatic factors, altitude, and slope are significant predictors for its occurrence and abundance. M. struthiopteris has high WA optima for summer temperature, pH, Ca, Mg, K, Na, cation exchange capacity (CEC), and base saturation, and a low optima for humidity and winter temperature. Of these, summer temperature (16.0 °C), Ca (63.1 mg 100 g dry soil-1), Mg (41.0 mg 100 g dry soil-1), K (23.6 mg 100 g dry soil-1), Na (5.0 mg 100 g dry soil-1), CEC (60.7 mEq 100 g dry soil-1), and base saturation (56.3%) have significant Gaussian logit responses, as do aspect (150.2°) and loss-on-ignition (9.4%). These results suggest that the occurrence and relative abundance of M. struthiopteris are well predicted by high soil base cations, a generally southern aspect, low organic content in the soil, and high July temperatures. 相似文献
73.
东北地区生态环境中的Se及其生态效应 总被引:3,自引:3,他引:0
对东北地区不同环境要素Se的分布与转化规律的研究表明,基岩、土壤、粮食和动物毛Se含量分别为0.12、0.150-0.540、0.0096-0.0765和0.0405-0.1414μg.g^-1;城市和农村儿童发Se含量为0.460和0.182μg.g^-1。根据不同要素Se含量和生态效应,可将该区分为Se适宜区、缺乏区和过渡区3个1级区,每个1级区又分为高Se源区的低Se源区。 相似文献
74.
75.
Prediction of the Reaction Equilibrium of Biocatalytic Reactions in Aqueous-Organic Two-Phase Systems 总被引:1,自引:0,他引:1
Anja E. M. Janssen Albert Van Der Padt Klaas Van't Riet 《Biocatalysis and Biotransformation》1995,12(4):223-240
Biocatalytic reactions can be carried out in aqueous-organic two-phase systems. Several models to describe the thermodynamically-determined equilibrium position in such systems have appeared in the literature. Some of these models are only valid for dilute systems, whereas others can also be used for nondilute systems. In this paper, these models are described and compared. It is explained in what way the equilibrium constants of each model can be used to predict the product concentration in different organic solvents. 相似文献
76.
Takashi Yamanaka 《Mycoscience》1995,36(1):17-23
Organic matter composition (lignin, holocellulose, 50% (v/v) methanol extract, water-soluble carbohydrate (WSC) and phenolics (WSP), petroleum ether extract, and ash) of A0 layer soil treated with 700 g/m2 of urea to promote ammonia fungi was investigated in a Japanese red pine (Pinus densiflora) forest. Nine species of fungi were found during the study period of 18 months after the treatment. Of these, seven species belong to the ammonia fungi. WSC content of the treated soil was lower than that of the control. Methanol extract content increased initially after the treatment, then decreased to below the control level. There were no consistent differences in other components between the treated plot and the control. The abilities to decompose cellulose, lignin, chitin, protein and lipid in 18 strains in 10 species of the ammonia fungi were also screened. Cellulose was not lysed byPseudombrophila deerata, Hebeloma spp. andLaccaria bicolor. Strong lignolytic activity was shown byLyophyllum tylicolor, Coprinus echinosporus andP. deerata. Chitin was decomposed byAmblyosporium botrytis, L. tylicolor, C. echinosporus andHebeloma vinosophyllum. All strains possessed proteolytic and lipolytic activities. Supply of glucose to the culture media resulted in weaker enzyme activities except for lignolytic ability. 相似文献
77.
Subtilisin Carlsberg was covalently attached to five macroporous acrylic supports of varying aquaphilicity (a measure of hydrophilicity). Kinetic parameters of the transesterification of S and R enantiomers of secphenethyl alcohol with vinyl butyrate, catalyzed by various immobilized subtilisins, were determined in anhydrous dioxane and acetonitrile. Enzyme enantioselectivity in acetonitrile, but not in dioxane, correlated with the aquaphilicity of the support; a mechanistic rationale for this phenomenon was proposed. Although the catalytic activity of immobilized subtilisin in anhydrous solvents strongly depended on enzyme pretreatment, the enantioselectivity was essential conserved. (c) 1994 John Wiley & Sons, Inc. 相似文献
78.
The application of liquid membrane extraction to the recovery of lactic acid from model systems and fermentation media was investigated. An experimental study of the facilitated transport of lactic acid using ALIQUAT 336 as a mobile carrier in a stirred transfer cell is reported. The effect of stirring speed, initial lactic acid concentration, carrier concentration, and NaCl as a reagent in the acceptor phase are considered. (c) 1994 John Wiley & Sons, Inc. 相似文献
79.
We report here on the characterization and isolation of two ecotypes of Chlorella vulgaris Beyerinck that coexist in wastewater reservoirs. One ecotype (C1) contains high amounts of chlorophyll b, is capable of autotrophic growth, and can utilize only a few organic solutes for growth. The second ecotype (C2) contains low amounts of chlorophyll b, requires vitamin B12, and can support its growth with a broad range of organic compounds. Of the two ecotypes, the latter showed slower growth rates when light was the sole source of energy. Cells of C2-type Chlorella attained higher photosynthetic activities than C1-type cells at saturating irradiances. However, their low chlorophyll b content and lower light utilization efficiency suggest that C2-type Chlorella contains relatively low amounts of light-harvesting antennae, a disadvantage in severely light-limited ecosystems like wastewater reservoirs. We hypothesize that the two Chlorella types coexist by adopting different lifestyles: C1-type cells rely largely on their photosynthetic potential for energy conservation and growth, whereas C2-type cells may exploit their heterotrophic properties for this purpose. 相似文献
80.
Changes in carbon storage in temperate humic loamy soils after forest clearing and continuous corn cropping in France 总被引:3,自引:0,他引:3
Soil samples from forest and agricultural sites in three areas of southwest France were collected to determine the effect
of forest conversion to continuous intensive corn cropping with no organic matter management on soil organic carbon (C) content.
Soils were humic loamy soils and site characteristics that may affect soil C were as uniform as possible (slope, elevation,
texture, soil type, vegetation).
Three areas were selected, with adjacent sites of various ages of cultivation (3 to 35 yr), and paired control forest sites.
The ploughed horizon (0-Dt cm) and the Dt-50 cm layer were collected at each agricultural site. In forest sites, each 10 cm
layer was collected systematically down to 1 meter depth. Carbon concentrations were converted to total content to a given
depth as the product of concentration, depth of sample and bulk density, and expressed in units of kg m-2. For each site and each sampled layer, the mineral mass of soil was calculated, in order to base comparisons on the same
soil mass rather than the same depth.
The pattern of C accumulation in forest soils showed an exponential decrease with depth. Results suggested that soil organic
carbon declined rapidly during the first years of cultivation, and at a slower rate thereafter. This pattern of decrease can
be fitted by a bi-exponential model assuming that initial soil organic carbon can be separated into two parts, a very labile
pool reduced during the first rapid decline and more refractory fractions oxidizing at a slower rate. Sampling to shallow
depths (0-Dt cm) resulted in over-estimation of the rate of carbon release in proportion to the initial amount of C, and in
under-estimation of the total loss of C with age. The results for the 0–50 cm horizon indicated that losses of total carbon
average about 50% in these soils, ranging in initial carbon content from 19 to 32.5 kg m-2. Carbon release to the atmosphere averaged 0.8 kg m-2 yr-1 to 50 cm depth during the first 10 years of cultivation. The results demonstrate that temperate soils may also be an important
source of atmospheric carbon, when they are initially high in carbon content and then cultivated intensively with no organic
matter management. 相似文献