Allelopathic effects of plant seeds on nitrification: Effects on nitrite oxidizers

Effects of cotyledon powder, from tea and oak seeds, on oxidation of NO 2 − to NO 3 − in nitrification were investigated. Presence of cotyledon powder or glucose in culture solutions greatly stimulated the rapid disappearance of NO 2 − from solutions. However, the amount of NO 3 − as the end product of nitrification was drastically reduced in the presence of seed cotyledon or glucose. Based on the results obtained from double enrichment experiments and also from experiments done with sterile and non-sterile soil-free solutions, it was concluded that the decrease in the amount of NO 3 − in nitrification seems to be due to fixation, volatilization and immobilization of nitrogen by organic substances present in ground cotyledons of tea and oak seeds; direct effects on nitrifying organisms seem to be negligible. ft∗|Present address: Department of Biology, Shiraz University, Shiraz 71454, Iran.