Root Morphology and Zn^2＋ Uptake Kinetics of the Zn Hyperaccumulator of Sedum alfredii Hance

Root morphology and Zn^2＋ uptake kinetics of the hyperaccumulating ecotype （HE） and nonhyperaccumulating ecotype （NHE） of Sedum alfredii Hance were investigated using hydroponic methods and the radiotracer flux technique. The results indicate that root length, root surface area, and root volume of NHE decreased significantly with increasing Zn^2＋ concentration in growth media, whereas the root growth of HE was not adversely affected, and was even promoted, by 500μmol/L Zn^2＋. The concentrations of Zn^2＋ in both ecotypes of S. alfredii were positively correlated with root length, root surface area and root volumes, but no such correlation was found for root diameter. The uptake kinetics for ^65Zn^2＋ in roots of both ecotypes of S. alfredii were characterized by a rapid linear phase during the first 6 h and a slower linear phase during the subsequent period of investigation. The concentration-dependent uptake kinetics of the two ecotypes of S. alfredii could be characterized by the Michaelis-Menten equation, with the Vmax for ^65Zn^2＋ influx being threefold greater in HE compared with NHE, indicating that enhanced absorption into the root was one of the mechanisms involved in Zn hyperaccumulation. A significantly larger Vmax value suggested that there was a higher density of Zn transporters per unit membrane area in HE roots.

The relationship between light intensity and nutrient uptake kinetics in six freshwater diatoms

In order to find effective measures to control diatom blooms, a better understanding of the physiological characteristics of nutrient uptake in diatoms is needed. A study of P and Si-uptake kinetics for diatom species from two light regimes was conducted at low（LL）,moderate（ML） and high light intensities（HL）（2, 25 and 80 μmol photons/（m2·sec））,respectively. The results showed that P uptake of diatoms was heavily influenced by historic light regimes. P affinity changed with growth and photosynthetic activity. The lowest half saturation constant for P uptake（Km（P）） was under HL for high-light adapted diatoms while the lowest half-saturation constant for low-light adapted diatoms was observed under LL. The Si half-saturation constant（Km（Si）） increased with increasing light intensities for pennate diatoms but decreased for centric diatoms. Diatom volumes were correlated with the maximum Si uptake rates（Vm（Si）） at HL and K m（Si）at ML and HL for six diatom species. Our results imply that when we assess the development of diatom blooms we should consider light intensity and cell volume in addition to ambient Si or P concentration. The relationship between light intensity and P-uptake suggests that we can find suitable methods to control diatom blooms on the basis of reducing phytoplankton activity of P-uptake and photosynthesis simultaneously.

Cadmium uptake and speciation changes in the rhizosphere of cadmium accumulator and non-accumulator oilseed rape varieties

Characteristics of cadmium （Cd） uptake kinetics and distribution of Cd speciation in the rhizosphere for Cd accumulator and nonaccumulator oilseed rape varieties were investigated under nutrient solution and rhizobox soil culture conditions. The results showed that the maximal influx （Vmax） for Cd^2＋ and Km were significantly different for the two oilseed rape varieties. The value of Vmax for Cd accumulator oilseed rape Zhucang Huazi was two-fold greater than that for oilseed rape Chuan you Ⅱ-93. The exchangeable Cd concentration in the rhizosphere was significantly lower than in non-rhizospheric soils supplemented with CdSO4 for both the varieties. Carbonate-bound Cd in the rhizosphere of Cd accumulator oilseed rape was significantly higher than that in the rhizosphere of nonaccumulator oilseed rape and non-rhizospheric soil. Cd accumulator oilseed rape had a higher Cd^2＋ affinity and more ability to uptake insoluble Cd in the soil than the non-accumulator oilseed rape.

Comparative studies on utilizing nitrogen capacity between two macroalgae Gracilaria tenuistipitata var. liui (rhodophyta) and Ulva pertusa (chlorophyta) II. Feedback controls of intracellular nitrogen pools on nitrogen uptake

The potential feedback by intracellular nitrogen pools on maximum N uptake (NH + 4) rate were determined for Gracilaria tenuistipitata var. liui and Ulva pertusa. The results of correlation matrix analyzing showed that the surge uptake of ammonium seemed related to rapid changes in small intracellular pools of inorganic nitrogen or small peptide and amino acids rather than to changes in TN content of the macroalgae. The assimilation rates of nitrogen of U. pertusa and G. tenuistipitata increased slowly during N starvation and were mainly regulated by amino acids and some incorporation of amino acids into macromolecules. From ecological point of view, the fast growing and uptaking nutrient U. pertusa is more suitable to improve water quality in integrated shrimp culture ponds in which external nutrient supplies are usually high and constant during the culture period, while G. tenuistipitata var. liui is more suitable to be polycultured in a waters with intermittence supply of nutrients.

Investigation of HO_(2) uptake mechanisms onto multiple-component ambient aerosols collected in summer and winter time in Yokohama,Japan

The heterogeneous loss of HO_(2)radicals onto ambient aerosols plays an important role in tropospheric chemistry.However,sparse investigation of the dominating parameters controlling the HO_(2)uptake coefficients onto ambient aerosols(γHO_(2))has largely hindered the application of the measuredγHO_(2)to the global spatial prediction.Here we induced an offine method using LFP-LIF technique to measure the kinetics of HO_(2)uptake onto ambient aerosols collected in summertime and wintertime in Yokohama city,a regional urban site near Tokyo,Japan.By controlling the dominating parameters which infuenceγHO_(2),we were able to investigate the detailed HO_(2)uptake mechanism.We characterized the chemical composition of the collected ambient aerosols,including organics,inorganics,transition metals ions,etc.and modeledγHO_(2)using different mechanisms.Results show thatγHO_(2)increased with the increase in RH,and the aerosol states(“dry”or wet/aqueous)have large effects onγHO_(2).With fixed RH and aerosol chemical composition,γHO_(2)was highly dependent on pH and inversely correlated with[HO_(2)]_0.By combing the measuredγHO_(2)values with the modeled ones,we found that both the HO_(2)self-reaction and transition metal-catalyzed reactions should be accounted for to yield a single parameterization to predictγHO_(2),and different chemical compositions may have collective effects onγHO_(2).Results may serve for extending theγHO_(2)values measured at one observation site to different environmental conditions,which will help us to achieve more accurate modeling results concerning secondary pollutant formation(i.e.,ozone).

Kinetic study of phytotoxicity induced by foliar lead uptake for vegetables exposed to fine particles and implications for sustainable urban agriculture

At the global scale, foliar metal transfer occurs for consumed vegetables cultivated in numerous urban or industrial areas with a polluted atmosphere. However, the kinetics of metal uptake, translocation and involved phytotoxicity was never jointly studied with vegetables exposed to micronic and sub-micronic particles（PM）. Different leafy vegetables（lettuces and cabbages） cultivated in RHIZOtest？ devices were, therefore, exposed in a greenhouse for 5, 10 and 15 days to various Pb O PM doses. The kinetics of transfer and phytotoxicity was assessed in relation to lead concentration and exposure duration. A significant Pb accumulation in leaves（up to 7392 mg/kg dry weight（DW） in lettuce） with translocation to roots was observed. Lead foliar exposure resulted in significant phytotoxicity, lipid composition change, a decrease of plant shoot growth（up to 68.2% in lettuce） and net photosynthesis（up to 58% in lettuce）. The phytotoxicity results indicated plant adaptation to Pb and a higher sensitivity of lettuce in comparison with cabbage. Air quality needs, therefore, to be considered for the health and quality of vegetables grown in polluted areas, such as certain megacities（in China, Pakistan, Europe, etc.） and furthermore, to assess the health risks associated with their consumption.

Synergistic and Antisynergistic Intracrystalline Diffusional Influences on Mixture Separations in Fixed-Bed Adsorbers

Separations of mixtures in fixed-bed adsorbers are influenced by factors such as(1)selectivity of adsorption,Sads,(2)diffusional time constants,Đi/rc 2,and(3)diffusion selectivity,Đ1/Đ2.In synergistic separations,intracrystalline diffusion of guest molecules serves to enhance the selectivities dictated by thermodynamics of mixture adsorption.In antisynergistic separations,intracrystalline diffusion serves to reverse the hierarchy of selectivities dictated by adsorption equilibrium.For both scenarios,the productivities of the desired product in fixed-bed operations are crucially dependent on diffusional time constants,Đi/rc 2;these need to be sufficiently low in order for diffusional influences to be effective.Also,the ratioĐ1/Đ2 should be large enough for manifestation of synergistic or antisynergistic influence.Both synergistic and antisynergistic separations have two common,distinguishing characteristics.Firstly,for transient uptake within crystals,the more mobile component attains supraequilibrium loadings during the initial stages of the transience.Such overshoots,signifying uphill diffusion,are engendered by the cross-coefficientsΓij(i≠j)of thermodynamic correction factors.Secondly,the component molar loadings,plotted in composition space,follow serpentine equilibration paths.If cross-coefficients are neglected,no overshoots in the loadings of the more mobile component are experienced,and the component loadings follow monotonous equilibration paths.The important takeaway message is that the modeling of mixture separations in fixed-bed adsorbers requires the use of the Maxwell−Stefan equations describing mixture diffusion employing chemical potential gradients as driving forces.

Toxicity evaluation of ZnO and TiO_2 nanomaterials in hydroponic red bean(Vigna angularis) plant:Physiology, biochemistry and kinetic transport

The toxicity and kinetic uptake potential of zinc oxide（Zn O） and titanium dioxide（TiO2）nanomaterials into the red bean（Vigna angularis） plant were investigated. The results obtained revealed that Zn O, due to its high dissolution and strong binding capacity, readily accumulated in the root tissues and significantly inhibited the physiological activity of the plant. However, TiO2 had a positive effect on plant physiology, resulting in promoted growth. The results of biochemical experiments implied that Zn O, through the generation of oxidative stress, significantly reduced the chlorophyll content, carotenoids and activity of stress-controlling enzymes. On the contrary, no negative biochemical impact was observed in plants treated with TiO2. For the kinetic uptake and transport study, we designed two exposure systems in which Zn O and TiO2 were exposed to red bean seedlings individually or in a mixture approach. The results showed that in single metal oxide treatments, the uptake and transport increased with increasing exposure period from one week to three weeks.However, in the metal oxide co-exposure treatment, due to complexation and competition among the particles, the uptake and transport were remarkably decreased. This suggested that the kinetic transport pattern of the metal oxide mixtures varied compared to those of its individual constituents.