Consistent land- and atmosphere-based U.S. carbon sink estimates.
(65/2707)
For the period 1980-89, we estimate a carbon sink in the coterminous United States between 0.30 and 0.58 petagrams of carbon per year (petagrams of carbon = 10(15) grams of carbon). The net carbon flux from the atmosphere to the land was higher, 0.37 to 0.71 petagrams of carbon per year, because a net flux of 0.07 to 0.13 petagrams of carbon per year was exported by rivers and commerce and returned to the atmosphere elsewhere. These land-based estimates are larger than those from previous studies (0.08 to 0.35 petagrams of carbon per year) because of the inclusion of additional processes and revised estimates of some component fluxes. Although component estimates are uncertain, about one-half of the total is outside the forest sector. We also estimated the sink using atmospheric models and the atmospheric concentration of carbon dioxide (the tracer-transport inversion method). The range of results from the atmosphere-based inversions contains the land-based estimates. Atmosphere- and land-based estimates are thus consistent, within the large ranges of uncertainty for both methods. Atmosphere-based results for 1980-89 are similar to those for 1985-89 and 1990-94, indicating a relatively stable U.S. sink throughout the period. (+info)
Bioremediation (natural attenuation and biostimulation) of diesel-oil-contaminated soil in an alpine glacier skiing area.
(66/2707)
We investigated the feasibility of bioremediation as a treatment option for a chronically diesel-oil-polluted soil in an alpine glacier area at an altitude of 2,875 m above sea level. To examine the efficiencies of natural attenuation and biostimulation, we used field-incubated lysimeters (mesocosms) with unfertilized and fertilized (N-P-K) soil. For three summer seasons (July 1997 to September 1999), we monitored changes in hydrocarbon concentrations in soil and soil leachate and the accompanying changes in soil microbial counts and activity. A significant reduction in the diesel oil level could be achieved. At the end of the third summer season (after 780 days), the initial level of contamination (2,612 +/- 70 microg of hydrocarbons g [dry weight] of soil(-1)) was reduced by (50 +/- 4)% and (70 +/- 2)% in the unfertilized and fertilized soil, respectively. Nonetheless, the residual levels of contamination (1,296 +/- 110 and 774 +/- 52 microg of hydrocarbons g [dry weight] of soil(-1) in the unfertilized and fertilized soil, respectively) were still high. Most of the hydrocarbon loss occurred during the first summer season ([42 +/- 6]% loss) in the fertilized soil and during the second summer season ([41 +/- 4]% loss) in the unfertilized soil. In the fertilized soil, all biological parameters (microbial numbers, soil respiration, catalase and lipase activities) were significantly enhanced and correlated significantly with each other, as well as with the residual hydrocarbon concentration, pointing to the importance of biodegradation. The effect of biostimulation of the indigenous soil microorganisms declined with time. The microbial activities in the unfertilized soil fluctuated around background levels during the whole study. (+info)
Enhanced tolerance of transgenic poplar plants overexpressing gamma-glutamylcysteine synthetase towards chloroacetanilide herbicides.
(67/2707)
A wild-type poplar hybrid and two transgenic clones overexpressing a bacterial gamma-glutamylcysteine synthetase in the cytosol or in the chloroplasts were exposed to the chloroacetanilide herbicides acetochlor and metolachlor dispersed in the soil. The transformed poplars contained higher gamma-glutamylcysteine and glutathione (GSH) levels than wild-type plants and therefore it was supposed that they would have an elevated tolerance towards these herbicides, which are detoxified in GSH-dependent reactions. Phenotypically, the transgenic and wild-type plants did not differ. The growth and the biomass of all poplar lines were markedly reduced by the two chloroacetanilide herbicides. However, the decrease of shoot and root fresh weights caused by the herbicides was significantly smaller in the transgenic than in wild-type plants. In addition, the growth rate of poplars transformed in the cytosol was reduced to a significantly lesser extent than that of wild-type plants following herbicide treatments. The effects of the two herbicides were similar. Herbicide exposures markedly increased the levels of gamma-glutamylcysteine and GSH in leaves of each poplar line. The increase in the foliar amounts of these thiols was stronger in the transgenic lines than in the wild type, particularly in the upper leaves. Considerable GST activities were detected in leaves of all poplar plants. Exposure of poplars to chloroacetanilide herbicides resulted in a marked induction of GST activity in upper leaf positions but not in middle and lower leaves. The extent of enzyme induction did not differ significantly between transgenic and wild-type poplars. Although the results show that the transgenic poplar lines are good candidates for phytoremediation purposes, the further improvement of their detoxification capacity, preferably by transformation using genes encoding herbicide-specific GST isoenzymes, seems to be the most promising way to obtain plants suitable for practical application. (+info)
The role of root exudates in aluminium resistance and silicon-induced amelioration of aluminium toxicity in three varieties of maize (Zea mays L.).
(68/2707)
Aluminium (Al) toxicity is widely considered to be the most important growth-limiting factor for plants in strongly acid soils (pH<5.0). The inhibition of root elongation in three varieties of maize (Zea mays L. vars Clavito, HS701b and Sikuani) was followed over the first 48 h of Al treatment, and during the initial 10 h elongation was determined on an hourly basis. The silicon (Si)-induced amelioration of Al toxicity was investigated by pre-treating seedlings for 72 h in nutrient solutions with 1000 microM Si before transfer into solutions with 0, 20 or 50 microM Al (without Si). Plants were either grown in complete low ionic strength nutrient solutions (CNS) or in low salt solutions of 0.4 mM CaCl2 (LSS). In addition, the role of root exudation of organic compounds as a mechanism of Si-induced alleviation of Al toxicity was investigated. Aluminium-induced inhibition of root elongation in the maize var. HS701b was observed within 1 h of Al exposure. After a lag time of at least 8 h, Si-induced alleviation of Al toxicity was observed in this variety when grown in LSS. In the Al-resistant var. Sikuani, Al-resistance was only observed after exposure to 50 microM Al, and not after exposure to 20 microM Al, suggesting that there exists a threshold Al concentration before the mechanisms of Al resistance are activated. Aluminium stimulated root exudation of oxalic acid in all three varieties, but exudate concentrations did not increase with either Al resistance or with Si pretreatment. Aluminium and Si triggered release of catechol and of the flavonoid-type phenolics: catechin, and quercetin. In the Al-resistant variety, Sikuani, Al-exposed plants pretreated with Si exuded up to 15 times more phenolics than those plants not pretreated with Si. The flavonoid-type phenolics, to date unconsidered, appear to play a role in the mechanism(s) of Si-induced amelioration of Al toxicity. (+info)
Zinc deficiency occurring in females. Report of two cases.
(69/2707)
The syndrome of dwarfism, hypogonadism, iron-deficiency anemia and geophagia, first reported in 1960 from Iran, was thought to be limited to males. In 1971-1972 two females with the same clinical features were observed over a 14-month period. The anemia responded rapidly to iron. Growth and sexual development occurred promptly when 120 mg of zinc sulfate was administered daily in conjunction with a well-balanced diet and iron supplement. This diet prior to the addition of zinc sulfate, resulted in gradual but much slower growth and sexual development. Observations in these two patients provide confirmation of the occurrence of human zinc deficiency in females, which responds to large doses of zinc salt. (+info)
Influence of effluent irrigation on community composition and function of ammonia-oxidizing bacteria in soil.
(70/2707)
The effect of effluent irrigation on community composition and function of ammonia-oxidizing bacteria (AOB) in soil was evaluated, using techniques of molecular biology and analytical soil chemistry. Analyses were conducted on soil sampled from lysimeters and from a grapefruit orchard which had been irrigated with wastewater effluent or fertilizer-amended water (FAW). Specifically, comparisons of AOB community composition were conducted using denaturing gradient gel electrophoresis (DGGE) of PCR-amplified fragments of the gene encoding the alpha-subunit of the ammonia monooxygenase gene (amoA) recovered from soil samples and subsequent sequencing of relevant bands. A significant and consistent shift in the population composition of AOB was detected in soil irrigated with effluent. This shift was absent in soils irrigated with FAW, despite the fact that the ammonium concentration in the FAW was similar. At the end of the irrigation period, Nitrosospira-like populations were dominant in soils irrigated with FAW, while Nitrosomonas-like populations were dominant in effluent-irrigated soils. Furthermore, DGGE analysis of the amoA gene proved to be a powerful tool in evaluating the soil AOB community population and population shifts therein. (+info)
Water balance across the cuticle of a soil insect.
(71/2707)
1. The water regime in soil commonly approaches equilibrium of water potential with the insects living there. 2. Even under these conditions, non-equilibrium processes have a significant effect on water movement through the cuticle of soil insects. 3. Measurements of water potential on either side of the cuticle of Costelytra zealandica larvae showed that equilibrium is not reached while the insect is alive. There is an active outward flow of water by thermoosmosis associated with the flow of heat from the insect. (+info)
Interactive effects of soil temperature, atmospheric carbon dioxide and soil N on root development, biomass and nutrient uptake of winter wheat during vegetative growth.
(72/2707)
Nutrient requirements for plant growth are expected to rise in response to the predicted changes in CO(2) and temperature. In this context, little attention has been paid to the effects of soil temperature, which limits plant growth at early stages in temperate regions. A factorial growth-room experiment was conducted with winter wheat, varying soil temperature (10 degrees C and 15 degrees C), atmospheric CO(2) concentration (360 and 700 ppm), and N supply (low and high). The hypothesis was that soil temperature would modify root development, biomass allocation and nutrient uptake during vegetative growth and that its effects would interact with atmospheric CO(2) and N availability. Soil temperature effects were confirmed for most of the variables measured and 3-factor interactions were observed for root development, plant biomass components, N-use efficiency, and shoot P content. Importantly, the soil temperature effects were manifest in the absence of any change in air temperature. Changes in root development, nutrient uptake and nutrient-use efficiencies were interpreted as counterbalancing mechanisms for meeting nutrient requirements for plant growth in each situation. Most variables responded to an increase in resource availability in the order: N supply >soil temperature >CO(2). (+info)