Activity of nitrifiers in relation to nitrogen nutrition of plants in natural ecosystem

Three aspects of the nitrate production in natural ecosystems are discussed, i.e. the population biology of nitrifying bacteria, the nitrate-producing activity of these organisms and the uptake of nitrate by higher plants. From the number of nitrifying bacteria no reliable estimate of the rate of nitrate production can be obtained and also estimates that are made using field-incubation and super(15)N-NH sub(4) super(+) techniques do not yield reliable data. Possibly the best results can be obtainted using Schimel's method to estimate the actual nitrification rate using super(15)N-NO sub(3) super(-), but this method has still not been tested under different sets of soil conditions. From the nitrate reductase activity and the chemical composition of the plant a picture can be obtained of the quantities of nitrate and ammonium that have been taken up. However, nitrate and ammonium are taken up in different proportions than they are produced.