Seed germination in response to chemicals: effect of nitrogen and pH in the media.

Seed germination generally presents a peak in the next growing season after a fire. Among other factors associated with fire are the increase of soil nitrogen and changes in the pH of the soil. In this study, we addressed the question, whether or not the germination response of eight species is linked with the increase in pH and nitrogenous compounds in the germination media? We assessed the separate and combined effects of nitrogenous compounds and pH on the percentage and rate of germination of seeds of Medicago arabica (L.) Hudson, Epilobium hirsutum L., Foeniculum vulgare Miller, Daucus carota L., Thapsia villosa L., Cynosurus cristatus L., Dactylis glomerata L. and Rumex crispus L. All these species are well represented in the Mediterranean ecosystems of the central-west Spain. Water and CaCl2 were used as controls. Nitrogenous compounds increased percent germination (level) and rate in three of the species studied. High pH negatively affected the germination rate of seeds from most species, but had no effect on the per cent germination of any of the species. The higher concentration of the nutritious solutions affected negatively the germination level and rate. The different germination responses of seeds of the studied species could not be exclusively attributed to pH values in the media, whereas the amount and form of Nitrogen in the media has a greater effect on it. These differences in germination are species dependent.

Response of Java citronella (Cymbopogon winterianus Jowitt) to toxic heavy metal cadmium.

Cadmium at 200 mg kg-1 soil and above concentrations was fatal as growth was inhibited ultimately leading to death of Java citronella (Cymbopogon winterianus Jowitt.). The surviving plants at 50 and 100 mg kg-1 treatments also exhibited pronounced retardation of growth and biomass yield. There was considerable reduction in the level of essential oil in herbage and oil quality deteriorated. Cadmium accumulation profile showed that highest accumulation was in root, followed by stem, leaf sheath and leaf. Very high accumulation in root for higher doses appeared to be the reason for fatality.