Minimum requirements for modelling bivalve carrying capacity

The concept of carrying capacity of an ecosystem fornatural populations is derived from the logisticgrowth curve in population ecology, and defined as themaximum standing stock that can be supported by agiven ecosystem for a given time. This definitionneeds to be modified for the exploitation ofecosystems. Carrying capacity for exploitation isdefined as the standing stock at which the annualproduction of a marketable cohort is maximized. Forbivalve suspension feeders, the dominant factordetermining the exploitation carrying capacity at theecosystem scale is primary production. At a localscale carrying capacity depends on physicalconstraints such as substrate, shelter and food supplyby tidal currents.We evaluate critically some existing models ofexploited ecosystems for shellfish cultivation inorder to formulate the minimum requirements of ageneric carrying capacity model. Generic models canbe developed for both the ecosystem scale and thelocal scale, depending on the aim of the modelling.Transport processes, sediment dynamics and submodelsfor organism and population level processes areminimum requirements for carrying capacity modelling. This revised version was published online in August 2006 with corrections to the Cover Date.     

Muscle ubiquinone in healthy physically active males

Thirty-five (35) healthy physically active males had muscle biopsies taken from their vastus lateralis muscle to analyze for ubiquinone (vitamin Q, UQ), oxidative (muscle fiber types expressed as %ST and citrate synthase activity, CS) and fermentative (lactate dehydrogenase, LD) profiles. Graded cycle ergometer exercise to determine the intensities corresponding to onset of blood lactate accumulation set to 4.0 mmol × 1^–1 (W_OBLA) and symptom limited exercise (maximal, W_SL) were also undertaken. Eleven (11) subjects had also recently participated in a marathon race. UQ was positively related to CS (r = 0.67, p < 0.001) and %ST (r = 0.60, p < 0.001) but not to LD. UQ was also positively related to exercise capacity and/or marathon performance (e.g. W_OBLA × kg^–1 BW, r = 0.70, p < 0.001). It was suggested that muscle UQ allocation in man was related to variables describing molecular oxygen availability, respiratory activity and oxidative energy releasing processes but not to fermentation activity. UQ allocation to ST fibers/CS activity was suggested to be due to the double role of UQ: 1) as a mitochondrial coenzyme (CoQ₁₀) and 2) as a nonspecific antioxidant.     

MPP+ toxicity in rat striatal slices: Relationship between non-selective effects and free radical production

Incubations of rat striatal slices have been used to assay MPP⁺ neurotoxicity. MPP⁺, at concentrations of 1 mM or higher, caused a marked increase in hydroxyl radicals, measured as malondialdehyde (MDA) accumulation, but not in nitric oxide production. At these doses, MPP⁺ showed an effect on dopamine terminals, causing a massive dopamine decrease, and on non-neuronal glial cells, where a marked reduction in glutamine synthetase activity was detected. At lower concentrations (25 μM), the toxic effect on dopaminergic endings was maintained without increasing malondialdehyde concentrations or inhibiting glutamine synthetase activity. The effect on glutamine synthetase was prevented by the addition to the medium of 0.5% dimethyl sulfoxide, a hydroxyl-radical scavenger, but this did not protect the effect of dopamine depletion. We propose that non-selective effects of MPP⁺, at doses of 1 mM or higher, are mediated by extracellular overproduction of hydroxyl radicals. The main factor responsible for this overproduction would not be the released dopamine but rather the MPP⁺ itself, through non selective inhibition of the mitochondrial respiratory chain or through a redox cycling that can trigger oxygen radical production.     

Direct and indirect oxidations by peroxynitrite, neither involving the hydroxyl radical

A new mechanism (Mechanism III) that combines features of mechanisms suggested earlier (Goldstein and Czapski, Inorg. Chem. 34:4041–4048; 1995; Pryor, Jin, and Squadrito Proc. Natl. Acad. Sci. USA 91:11173–11177; 1994) is proposed for oxidations by peroxynitrite. In Mechanism III, oxidations by peroxynitrite can take place either directly by ground-state peroxynitrous acid, ONOOH, or indirectly by ONOOH*, where ONOOH* is an activated form of peroxynitrous acid. In the direct oxidation pathway the reaction is first order in peroxynitrite and first order in substrate, and the oxidation yield approaches 100%. In the indirect oxidation pathway the reaction is first order in peroxynitrite and zero order in substrate. In the presence of sufficient concentrations of a substrate that reacts by the indirect oxidation pathway, about 50–60% of the ONOOH directly isomerizes to nitric acid, and about 40–50% of the ONOOH is converted into ONOOH*. Thus, the oxidation yields by the indirect pathway will not exceed 40–50%, and there will always be a residual yield of nitrate even in the presence of very high concentrations of the substrate. Competitive inhibition studies with various free radical scavengers showed that in some cases these scavengers have no effect on oxidation yields. In others, only partial inhibition was observed, far less than that predicted from to the known rate constants for the reactions of these scavengers with the hydroxyl radical. There are some cases where the extent of inhibition correlates well with the known rate constants of the reactions of these scavengers with hydroxyl radical; nevertheless, even in these cases, the involvement of hydroxyl radicals in indirect oxidations by peroxynitrite is ruled out on the basis of kinetics and oxidation yields. Thus, direct oxidations by peroxynitrite are explained in terms of ONOOH, and indirect oxidations in terms of ONOOH*, and substrates can react by one or both of these pathways.     

Changes in Al and Fe crystallinity and P sorption capacity in a flood-plain forest soil subjected to artificially manipulated flooding regimes in field mesocosms

Changes in noncrystalline Fe and P sorption capacity in soils subjected to flooding and draining for rice cultivation sparked interest in how periodic flooding in natural riparian wetlands influences soil chemistry and P retention. We examined monthly changes in soil oxalate-extractable Al and Fe, NaOH-extractable Al, DCB-extractable Fe, and P sorption capacity as a function of flooding regime in artificially manipulated field mesocosms installed in a floodplain forest along the Ogeechee River, near Savannah, GA. We hypothesized that: (1) flooding would cause increases in both oxalate-extractable (noncrystalline) Al and Fe concentrations and P sorption capacity, and, (2) this effect would be augmented by increased flooding duration and periodicity. Flooding resulted in increases in oxalate-extractable Al in flooded-drained and periodically flooded soils, decreases in crystalline Fe in all flooding treatments, and an increase in P sorption capacity in flooded-drained soils. However, consistent trends were not observed across all treatment regimes. Potential confounding factors include a lack of synchronicity of experimental and natural flooding cycles, spatial variability of soil chemistry, and increased soil wetness in the treatment field, variables that should be considered in future attempts at elucidating relationships between flooding, soil chemistry and wetland function.     

螺旋藻培养液吸收CO2特性的研究

培养液中含有高浓度的ＨＣＯ和ＣＯ,活跃进行的ＣＯ２,ＨＣＯ和ＣＯ３种碳源形式相互转变的化学反应,构成了螺旋藻培养液不同于其它藻类培养液的显著特征。定量研究了ＣＯ２吸收速率与碳源浓度、温度、ｐＨ值、盐度、培养液运动状态的关系,利用培养液吸收ＣＯ２的物理模型解释了碳源浓度、ｐＨ值、培养液运动状态影响ＣＯ２吸收速率的机理。对化学反应是否影响ＣＯ２吸收速率这一有争议的问题进行了探讨,在肯定化学反应影响的前提下,指出化学反应的影响能否被观察到,显著程度如何,关键在于培养液的运动状态。根据实验结果,给出了利用“气罩法”添加ＣＯ２,所需气罩面积与产量、碳源浓度、培养液运动状态、培养面积数量关系的理论值。使用培养液的“ＣＯ２容量”的概念,说明利用ＣＯ２为碳源培养螺旋藻与其它藻类相比,可以得到更高的碳源利用率,从而产生更大的效益。     

博莱霉素A_5、Fe~（2＋）、O_2混合的化学发光研究

利用超弱发光仪测得博莱霉素Ａ５（ＢＬＭＡ５）、Ｆｅ２＋、Ｏ２混合物有微弱化学发光,最大发射波长约为５９０ｎｍ;发光强度随ＢＬＭＡ５或Ｆｅ２＋浓度增大而增强;·ＯＨ清除剂甘露醇对发光无影响;Ｃｕ２＋、ＥＤＴＡ、ＤＮＡ对化学发光均有不同程度的抑制作用。上述结果说明：ＢＬＭＡ５与Ｆｅ２＋、Ｏ２混合可形成某种激发态复合物,并显示该激发态的形成与·ＯＨ无关,提示该激发态复合物可能是ＢＬＭＡ５降解ＤＮＡ的启动因子。     

The effects of different soil water potentials, temperature and salinity on germination of seeds of the desert shrub Zygophyllum dumosum

The effects of different soil water potentials, temperature and NaCl concentration on seed germination of Zygophyllum dumosum Boiss., a common shrub in Israeli deserts, was investigated. Seeds had to be exposed to constant field capacity conditions (–0.0316 MPa) for a minimal period of two days before germination could start. Maximal germination under such conditions occurred after four days or more. Under simulated conditions of gradual dehydration of the soil, seeds were inhibited either at low soil water potentials (–0.10 to –10.00 MPa) or at high ones (–0.002 to –0.0398 MPa). Germination of Z. dumosum was independent of temperature in the range of 10–25°C, but strongly inhibited at 30 and 35°C. At 20°C germination was inhibited by salinity of the medium but still occurred (0.5%) even at a concentration of 0.5 M NaCl.     

Effects of toxins from two strains of Verticillium lecanii (Hyphomycetes) on bioattributes of a predatory ladybeetle, Delphastus catalinae (Col., Coccinellidae)

Abstract:  The aim of this study was to test the hypothesis that the whitefly ( Bemisia tabaci ; Hom., Aleyrodidae) predator ladybird beetles, Delphastus catalinae (Col., Coccinellidae), are not adversely affected in the field by the crude insecticidal toxins extracted from two strains of the fungus Verticillium lecanii , V3450 and Vp28. We developed a method to evaluate sublethal toxicity and its effects on consumption and functional response of D. catalinae . The crude toxins have low toxicity against beetle larva with LC₅₀ values of 1942 (1393–2710) and 2471 (1291–4731) p.p.m., respectively (approximately 10- and 12-fold of field rate of application 200 p.p.m.). The adult beetles had less sensitivity to crude toxins with LC₅₀ values of 4260 (3376–5375) and 4426 (1734–11298) p.p.m., respectively (approximately 20- and 22-fold of field rate 200 p.p.m.). The consumption and foraging capacity were significantly impaired especially in the second-instar larval beetles which took longer time (more than twice of the control beetles) to consume whitefly eggs after exposure to toxins, although D. catalinae suffered no significant effect on fecundity and longevity, when exposed to a toxin dilution of field rate. The data suggest that spraying of V. lecanii or its toxins should be avoided in the field having immature stages of D. catalinae .     

Survival and recovery of Phytophthora capsici and oomycetes in tailwater and soil from vegetable fields in Florida

A current trend in Florida agriculture to conserve water is to irrigate with surface runoff water (tailwater) recovered in retention ponds and canals. Water filtration and lemon leaf baiting recovered Phytophthora capsici and other plant pathogenic Oomycetes in runoff water from ponds and canals. A total of 196 isolates of Phytophthora spp. and 471 isolates of Pythium spp. were recovered. Phytophthora spp. included P. capsici, P. cinnamomi, P. lateralis, P. nicotianae, P. citricola, P. cryptogea and P. erythroseptica. Species of Pythium were P. aphanidermatum, P. catenulatum, P. helicoides, P. irregulare, P. myriotylum, and Pythium‘group F’. Isolates of P. aphanidermatum, P. irregulare, P. myriotylum, and Pythium‘group F’ were pathogenic on pepper and tomato. Recovery of P. capsici propagules was related to soil moisture‐holding capacity and time interval but not temperature. Recovery of P. capsici propagules at 100% soil moisture‐holding capacity and 30° C was 57 days. In tailwater, recovery of propagules of P. capsici was 63 days at 24°C to 25°C. The potential exists to reintroduce and disseminate species of Phytophthora and Pythium when using tailwater for irrigation or other practices.