Nitrogen response of herbs and graminoids in experiments with simulated acid soil solution

Sand-solution experiments involving 15 herbs and 13 graminoids were perform ed to study how biomass was effected by N concentrations of 50, 250 and 125 0 mu M, respectively, in a simulated acid forest soil solution. The concent rations of the various components corresponded with those found in soil sol utions in deciduous forests of southern Sweden. The experiments were undert aken to study the extent to which species are affected differently by incre ases in the concentration of N as compared with that of the other nutrients . The underlying hypothesis was that species with a high demand for N and a lesser demand for other nutrients are particularly competitive in areas wi th acidic soil and a high degree of N deposition. The graminoids were found to be favoured more than the herbs by the addition of N, 46% displaying a significantly greater biomass at 250 than at 50 mu M N as compared with onl y 7% for the herbs. Some species attained their highest biomass at 1250 mu M N and others at 50 mu M N. It is concluded that at the highest N concentr ation, growth was limited for most species by the supply of other nutrients and that at the intermediate N concentration the graminoids were more effi cient than the herbs in utilising N. It was found that the Ellenberg N indi cator values could not be used to predict biomass production under the cond itions studied since they failed to adequately explain the response to trea tment by N.