Weiguo Fu, Pingping Li, Yanyou Wu, Jianjian Tang, 2012. Effects of different light intensities on anti-oxidative enzyme activity, quality and biomass in lettuce. Hort. Sci. (Prague), 39: 129-134.Recently, the worldwide demand for romaine lettuce (Lactuca sativa L.) has been increasing. Thus, regulation measures of supplementary or shading light are often used in the production of lettuce in some regions. However, inconsistent results on the light saturation point of lettuce from previous studies do not facilitate the regulation of light intensity. In the present study, the effects of different light intensities on anti-oxidative enzyme activity, yield and quality of lettuce were investigated. The results reveal the following: (1) judged by the dynamics of anti-oxidative enzyme activity, there was no light stress to occurr in the 100, 200 and 400 μmol/m 2 s treatments, a mild light stress occurred in the 600 μmol/m 2 s treatment, and a serious light stress occurred in the 800 μmol/m 2 s treatment; (2) increased light intensity gradually reduced the contents of soluble protein and nitrate in lettuce, whereas the content of soluble sugar remarkably increased. The biomass of a single plant of lettuce in the 600 µmol/m 2 s treatment was the highest and second highest in the 400 µmol/m 2 s treatment but was the lowest in the 100 µmol/m 2 s treatment. No significant difference in the biomass of single plant was observed between the 400 and 600 µmol/m 2 s treatments. Based on these results, the range of 400 µmol/m 2 s to 600 µmol/m 2 s is a recommendable light intensity for lettuce production.

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Background and aims -The niche theory has become one of the fundamental theories to explain species coexistence. In the present study, the relationships between competition/ facilitation and species niche, and between displacement /coexistence and species niche were further explored by studying the realized niche dynamics of species along a succession process. Materials and methods -By using space series to replace time courses, the niche dynamics of species involved in the plant community succession process in the Waterfront Wetland of Yangtze Rivers Lower Reach, China, were studied by using the formula described by Levins and Pianka. Key results -Results showed that every succession stage community was dominated by the species with the highest or/and second highest niche breadths, revealing that these species had broader environmental tolerances and were able to use a wider range of resources. In general, niche overlaps were greater among species with higher niche breadths. The total average niche overlaps of all paired species at different succession stages first increased, reached its maximum in the late-middle stage, and then finally decreased slightly in the late stage in the entire succession process. Conclusion -The dynamic characteristics of niche of species reflect the process of displacement of species along the community succession process. The higher niche overlaps reflect the instability and transition state of plant communities along the successional process. Facilitation, as well as competition, occurs in the different species with higher niche overlap.

In the initial stage of the rainfall, the nutrient element phosphorus (P) in the farmland, one of the most important factors causing agricultural non-point source pollution, flows into agriculture drainage ditches rapidly, and an instantaneous phosphorus peak value in the ditch water often occurs. Aerated concrete with high P adsorption properties was chosen as the experiment material in the laboratory to reduce the instantaneous P peak value in the drainage water in the initial stage of the rainfall. The three total P (TP) concentrations of the simulated drainage water (1.0, 2.0, and 3.0 mg/L) stood for three treatments were designed in the adsorption experiment; the same three TP concentrations of the simulated drainage water and the three TP concentrations of the simulated natural water (0.2, 0.3, and 0.4 mg/L) stood for nine treatments in the desorption experiment. The sponge effect of the aerated concrete on the P adsorption-desorption was explored by studying the dynamics of the P adsorption-desorption of the aerated concrete with an increase in the experiment’s time. The results showed the following details: (1) Both the adsorption rate and desorption rate of the aerated concrete decrease with an increase in the experiment’s time. The initial adsorption is dominant during the entire adsorption, as with the initial desorption during the entire desorption. (2) The adsorption capacity of the aerated concrete slightly decreases with the increase in the re-adsorption, whereas the desorption capacity of the aerated concrete significantly decreases with the increase in the re-desorption. Thus, the aerated concrete can be introduced into the agricultural drainage ditch to reduce the instantaneous P peak value in the drainage water in the initial stage of the rainfall, and potential further studies should explore the relationship between the different drainage water loads and the amount of the aerated concrete.