Production and Consumption of NO in Forest and Pasture Soils from the Amazon Basin

NO production and the rate constant of NO consumptionin soil samples from Amazonian forest and pasturesites were determined in the laboratory. The purposewas to study NO production and consumption in soilsfrom both types of land use as functions of soiltemperature and soil moisture. NO productionincreased exponentially with soil temperature. Thedegree of increase depended on soil moisture,indicating that the response of NO production to achange in soil temperature is most pronounced at acertain intermediate soil moisture. NO productionpeaked at a soil moisture of 0.10 g g^-1, correspondingto 0.27 and 0.38 water-filled pore space for forestand pasture soils, respectively. The optimum soilmoisture for which maximum NO release was observedwas independent of soil temperature. NO consumptionwas most efficient at high soil temperatures andunder dry soil conditions. NO release wasapproximately 10 times larger for forest than pasturesoil. The difference may be related to the higherNO₃ ^- content in forest soil.     

Molecular characterization of symbiotic algae (Symbiodinium spp.) in soritid foraminifera (Sorites orbiculus) and a scleractinian coral (Orbicella annularis) from St John,US Virgin Islands

The exchange of Symbiodinium symbionts among scleractinian and soritid hosts could facilitate acclimatization to changing conditions by establishing novel symbiotic unions better tuned to prevailing conditions. In this study, we compare the communities of Symbiodinium spp. in neighboring populations of Orbicella annularis and Sorites orbiculus from St. John, US Virgin Islands, using operational taxonomic unit (OTU) clustering of cloned internal transcribed spacer 2 (ITS-2) rDNA sequences. We tested for partitioning of Symbiodinium OTUs by host and depth within and between two sites to explore the potential for symbiont exchange between hosts and light-dependent microhabitat specialization. An apparent lack of overlap in Symbiodinium communities (13 OTUs representing 7 clades) hosted by O. annularis and S. orbiculus suggests that exchange among these hosts does not occur. A low number of novel clade G ITS-2 sequences were found in one O. annularis and one S. orbiculus. A phylogenetic analysis of these sequences revealed them to be sub-clade G2 Symbiodinium, which are most commonly hosted by excavating clionid sponges. A permutational MANOVA revealed within host differences in the partitioning of Symbiodinium OTUs by site but not depth. This finding highlights the potential roles of either dissimilar environmental conditions between sites, or at least partial separation between populations, in determining the types of Symbiodinium contained in different hosts on a spatial scale of a few kilometers.     

Effects of Arbuscular mycorrhizal fungi isolated from white clovers (Trifolium repens L) on soil bacteria and fungi

White clover potted experiments were performed to investigate the effects of seven indigenous arbuscular mycorrhizal fungi (AMF) communities isolated from different test plots subjected to long-term fertilisation on soil enzyme activities, number of soil bacteria and fungi. The results showed that the inoculation of arbuscular mycorrhizal fungi communities increased the mycorrhizal infection rate of the plants and promoted the growth of plants. The Mnp treatment was most effective. The shoot biomass, root biomass, potassium and nitrogen uptake of the white clover in Mnp treatment group were increased by 61.54%, 84.00%, 62.50% and 46.71% respectively, compared with those in non-inoculation treatment. The inoculation of AMF communities had little effect on the number of bacteria in the soil, but significantly increased the number of soil fungi. Mnk treatment group had the highest number of fungi in the soil, which was 9.91 times that of the non-inoculation treatment group. The catalase and dehydrogenase activities were both significantly improved in Mnp treatment by 28.12% and 205.38% respectively, compared with those of the control treatment (-M). The urease, invertase and cellulase activities reached the highest levels in the Mck treatment; they were increased by 142.79%, 41.17% and 77.62% respectively, compared with those of the control treatment. Pearson correlation analysis showed that the soil enzyme activity was not correlated with the mycorrhizal infection rate, but correlated with the spore number of the AMF community. The impact of AMF community on soil quality is important for us to understand the function of the ecosystems. Relevant study provides important guidance for maintaining the balance of the soil-plant system and the development of sustainable agriculture.     

Direct numerical simulations of boundary condition effects on the propagation of density current in wall-bounded and open channels

The propagation of density current under different boundary conditions is investigated using high resolution direct numerical simulations (DNS). A revised Kleiser and Schumann influence-matrix method is used to treat the general Robin type velocity boundary conditions and the related “tau” error corrections in the numerical simulations. Comparison of the simulation results reveals that the boundary conditions change the turbulent flow field and therefore the propagation of the front. This paper mainly focuses on the effects of boundary conditions and initial depth of the dense fluid. The differences in energy dissipation and overall front development in wall-bounded and open channels are examined. Through DNS simulations, it is evident that with the decrease of initial release depth ratio ( $D/H$ ), the effect of the top boundary becomes less important. In wall-bounded channels, there are three distinctive layers in the vertical distribution of energy dissipation corresponding to the contributions from bottom wall, interface, and top wall, respectively. In open channels, there are only two layers with the top one missing due to the shear free nature of the boundary. It is found that the energy dissipation distribution in the bottom layer is similar for cases with the same $D/H$ ratio regardless the top boundary condition. The simulation results also reveal that for low Reynolds number cases, the energy change due to concentration diffusion cannot be neglected in the energy budget. To reflect the real dynamics of density current, the dimensionless Froude number and Reynolds number should be defined using the release depth $D$ as the length scale.     

A high-order well-balanced weighted compact nonlinear scheme for solving the pollutant transport model

Environmental Fluid Mechanics - Pollutant transport in flows may cause potential risk on the local ecological system and public health. Numerical prediction of pollutant transport driven by shallow...     

Effect of red mud addition on the fractionation and bio-accessibility of Pb,Zn and As in combined contaminated soil

Using soil incubation experiments, the effect of red mud addition on the fractionation and bioaccessibility of Pb, Zn and As in combined contaminated soil was studied. The results showed that red mud addition could significantly decrease the concentration of HOAc-extractable Pb and Zn in soil. Compared with the control, 5% red mud addition could significantly reduce the concentrations of HOAc-extractable Pb and Zn in soil after 1, 2 and 3 months of incubation [62.5, 65.3 and 73.5% decrease (Pb), 56.7, 65.8 and 67.4% decrease (Zn)]. Whereas adding red mud could remarkably increase the concentrations of specific absorbed As and residual As in soil. The result of a simple bioavailability extraction test (SBET) indicated that all treatments with red mud addition markedly reduced the concentration of bioaccessible Zn but increased the concentration of bioaccessible As in soil, while having little effect on the concentration of bioaccessible Pb in soil. After 3 months incubation, all treatments including 1, 2 and 5% red mud addition reduced the concentration of bioaccessible Zn by 53.1–56.7% compared with the control, but increased the concentration of bioaccessible As by 1.81–6.25 times. The results suggested that red mud is an additive with potential for the remediation soil contaminated soil by combinations of heavy metals, although it should be added based on the different heavy metals in the soil. Combined use of red mud and hyperaccumulators to remediate heavy metal contaminated soil needs further study.     

Empirical assessment of state-and-transition models with a long-term vegetation record from the Sonoran Desert

Resilience-based frameworks, including state-and-transition models (STM), are being increasingly called upon to inform policy and guide ecosystem management, particularly in rangelands. Yet, multiple challenges impede their effective implementation: (1) paucity of empirical tests of resilience concepts, such as alternative states and thresholds, and (2) heavy reliance on expert models, which are seldom tested against empirical data. We developed an analytical protocol to identify unique plant communities and their transitions, and applied it to a long-term vegetation record from the Sonoran Desert (1953-2009). We assessed whether empirical trends were consistent with resilience concepts, and evaluated how they may inform the construction and interpretation of expert STMs. Seven statistically distinct plant communities were identified based on the cover of 22 plant species in 68 permanent transects. We recorded 253 instances of community transitions, associated with changes in species composition between successive samplings. Expectedly, transitions were more frequent among proximate communities with similar species pools than among distant communities. But unexpectedly, communities and transitions were not strongly constrained by soil type and topography. Only 18 transitions featured disproportionately large compositional turnover (species dissimilarity ranged between 0.54 and 0.68), and these were closely associated with communities that were dominated by the common shrub (burroweed, Haplopappus tenuisecta); indicating that only some, and not all, communities may be prone to large compositional change. Temporal dynamics in individual transects illustrated four general trajectories: stability, nondirectional drift, reversibility, and directional shifts that were not reversed even after 2-3 decades. The frequency of transitions and the accompanying species dissimilarity were both positively correlated with fluctuation in precipitation, indicating that climatic drivers require more attention in STMs. Many features of the expert models, including the number of communities and participant species, were consistent with empirical trends, but expert models underrepresented recent increases in cacti while overemphasizing the introduced Lehmann's lovegrass (Eragrostis lehmanniana). Quantification of communities and transitions within long-term vegetation records presents several quantitative metrics such as transition frequency, magnitude of accompanying compositional change, presence of unidirectional trajectories, and lack of reversibility within various timescales, which can clarify resilience concepts and inform the construction and interpretation of STMs.     

Screening and degradation characteristics of a tetracycline-degrading bacterial strain北大核心CSCD

Tetracycline is widely used in livestock and poultry breeding industry, which can cause serious problems to the environment. Antibiotic pollution has become an important environmental issue. This study aimed to isolate and identify a well-functioning tetracycline-degrading bacteria strain from activated sludge and to investigate its optimum degradation conditions. The strain was identified through morphological features, Gram staining, and the sequence analysis of 16S rRNA. Furthermore, the temperature, initial pH of the medium, inoculation amount, and type of metallic salt were analyzed to investigate the tetracycline degradation performance of the isolated strain. Based on the single factor test, the method of response surface analysis was adopted to optimize the degradation condition. The strain was named TTC-1 and identified as Klebsiella pneumoniae. The optimum condition for tetracycline degradation was determined as follows: temperature of 34.4 °C, pH of 7.22, and MnSO4 concentration of 0.32 g/L. Under this optimum condition, the predicted tetracycline degradation rate was 93.77%, whereas the observed value was 94.26%. The experimental results showed that the proposed model had high accuracy. TTC-1 showed a good performance in degrading tetracycline, which can provide reference for the bacteria during the biological treatment of tetracycline containing wastewater. © 2018 Science Press. All rights reserved.     

Protective effect of exogenous nitric oxide and salicylic acid on the photosynthetic apparatus of tomato seedling leaves under NaCl stress北大核心CSCD

Using the tomato variety 'Qin Feng Bao Guan' as experimental material, and by the hydroponics nutrient solution method, we investigated the effects of single and compound applications of nitric oxide (NO) donor sodium nitroprusside (SNP) and salicylic acid (SA) on the gas exchange and chlorophyll fluorescence parameters, RuBisCO activation, CO2 response curve, photosynthetic pigment content, and xanthophyll cycle in seedling leaves under an NaCl stress of 100 mmol/L. The main findings were as follows: (1) Single or combined applications of SNP and SA could increase the net photosynthetic rate (Pn), stomatal conductance (Gs), PS II maximal photochemistry efficiency (Fv/Fm), antenna conversion efficiency (Fv'/Fm'), practical photochemical efficiency (φPS?), photochemical fluorescence quenching coefficient (qP), and chlorophyll fluorescence decay rate (Rfd) of tomato seedling leaves at different rates, and significantly reduce the intercellular CO2 concentration (Ci), original fluorescence (Fo), and PS II non-photochemical fluorescence quenching coefficient (NPQ), after NaCl stress treatment. The strongest effect was observed after applying a combination of SNP and SA. (2) Under NaCl stress, the decrease of CO2 carboxylation efficiency (CE), RuBP maximum regeneration rate (Jmax), RuBisCO and its activation enzyme activity, and the maximum carboxylation rate (Vc max) in tomato seedling leaves could be effectively relieved by SNP, SA, or SNP + SA applications; however, SNP + SA treatment had the strongest effect. (3) Single or combined applications of SNP and SA could effectively inhibit the decrease of the contents of photosynthetic pigments (chlorophyll a, chlorophyll b, and carotenoids), the ratio of chlorophyll a and chlorophyll b, xanthophyll cycle pool size (V + A + Z), and the increase of the de-epoxidation extent of the xanthophyll cycle (A + Z)/(V + A + Z). The combined application of SNP and SA had the most prominent effect. In conclusion, the heat dissipation of the antenna, which is dependent on the xanthophyll cycle, is not the physiological mechanism for the protection of the photosynthetic apparatus by exogenous NO, SA alone, or compound treatment in tomato seedling leaves under NaCl stress. It is the main reason for the increase of photosynthetic function and enhanced salt tolerance of leaves tomato seedlings that the protection of PS II and its primary electron acceptor quinone (QA) downstream electron transfer patency, and the improvement of CO2 assimilation activity by application of exogenous NO, SA alone, or a combination of the two; synergistic effects were observed after using a combination of SNP and SA. © 2018 Science Press. All rights reserved.