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The toxicity of organic chemicals to Vibrio fischeri, river bacteria, algae, Daphnia magna and fishes were analysed. The results showed that the toxicity of chemicals to narcotics was dependent on hydrophobicity. A single model for both polar and non-polar narcotics was developed by inclusion of a polarity descriptor as well as the hydrophobic parameter. The highly hydrophobic polar narcotics could be treated as non-polar narcotics because their polar functional group(s) make(s) a relatively small contribution to polarity as compared with their hydrophobicity. In order to investigate the toxic mechanism of action for reactive compounds, the response-surface approach was used to develop models derived from easily calculated descriptors. The stepwise analysis selected the octanol/water partition coefficient and a polarity descriptor to parameterize bio-uptake and reactivity, respectively, for seven species. Benzoic acids can be easily absorbed into the unicellular bacteria, but this is not the case for multicellular D. magna and fish. Their toxicity to V. fischeri is much higher than that to D. magna and carp. Regression analysis was performed based on the model that we developed for ionizable compounds. Good correlations were observed by introducing the correction factor for ionizable compounds. The toxic mechanisms are discussed.

Laser-induced breakdown spectroscopy combined with the random forest (RF) algorithm was proposed for the classification of ten iron ore samples.

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Summary1. Root and shoot competition affect plant growth in different ways, but their effects on reproductive allocation have not been investigated. If root and shoot competition affect reproductive output in a population differently, this will influence the evolution of plant populations growing under various competitive regimes. 2. We conducted a field experiment to investigate the effects of root, shoot and full competition from naturally occurring surrounding vegetation on growth and reproduction of an annual plant, Chenopodium acuminatum, under low and high soil fertility. Root competition was eliminated by inserting a PVC pipe vertically into the soil around target individuals, and shoot competition was removed by installing inverted wire cones above-ground. Plants were measured after 11 weeks of growth. The relationships between reproductive (R) and vegetative (V) biomass among treatments were compared. 3. Without fertilizer, the competitive response of target plants to root competition was greater than that to shoot competition, while in the fertilized treatment, the opposite was the case. Fertilization increased target plant size under no or root competition, but did not affect mean plant size for individuals experiencing shoot or full competition. Variation in size among target plants was highest under shoot competition at high fertility. 4. The slope of log R-log V relationship under fertilized conditions was significantly higher than without fertilizer addition. The slope was higher under shoot and full competition than under root or no competition at both fertility levels. There were many more small individuals when competition was for light than for soil resources. These small individuals developed more slowly and had fewer flowering branches and lower reproductive allocation at harvest than large individuals. 5. Synthesis. Our results demonstrated that shoot competition affects the observed pattern of reproductive allometry among individuals in the field, and this has implications for the fitness of competing plants. The steeper log R-log V slope of populations competing above-ground may intensify the role of directional selection under light competition, making the effects of shoot competition more important than those of root competition for the evolution of weeds in fertile environments.

Grazing intensity is one of the most important factors influencing soil properties variations in rangeland ecosystem. This research aimed to study the features of soil properties under different grazing intensity in a Kobresia parva-meadow on the Qinghai-Tibetan Plateau, China. Results showed that soil organic matter (SOM), soil organic carbon (SOC), and total nitrogen (N) significantly decreased with an increase grazing intensity and total and available potassium (K), and C/N ratio exhibited a similar pattern. However, there were not significant differences between warm-season pasture (WSP) and cool-season pasture (CSP). In addition, results indicated that soil P was a limited factor, and N was sensitive to grazing intensity in Kobresia parva alpine meadow grazing ecosystem. Therefore, our study demonstrated that soil properties, such as soil carbon and nitrogen, generally decreased with the increasing of grazing intensity in studied Kobresia parva-meadow on the Qinghai-Tibetan Plateau.

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