Investigations into chemical aspects of peatland ecology with special reference to nitrogen fixation

Abstract

The first part of this thesis examines nitrogenase activity in Alnus,Myrica, Anabaena, Plectonema, and peat, with particular attention to field use of the acetylene reduction assay. The rate of nitrogenaseactivity was found to be very sensitive to temperature change, except for blue-green algae in reduced light. Low p0(_2) values reduce the rate of nitrogenase activity by nodules of Alnus and Myrica. Nitrogenase activity in Anabaena occurs at 40%ºC in condition of low p0(_2) . Characteristics of acetylene reduction by peat indicate that the reaction is caused by a living enzyme. A mixture of aerobic and anaerobic conditions stimulates acetylene reduction by peat, therefore it is suggested that microbial associations may be important for heterotrophic nitrogen fixation in peat. Theoretical and practical aspects of the relationship between nitrogenise activity and temperature are discussed. The second part of the thesis is concerned with the distribution of certain elements, and heterotrophic nitrogenase activity in relation to peatland ecology. The nutrient ecocline in mires is defined by a floristic gradient, in relation to which the above mentioned factors are examined. Heterotrophic nitrogenase activity was estimated in peat collected from eleven different mire complexes; a trend of increasing activity was observed from bogs to rich fens, with a significant decline in extreme rich fens. The amounts of Ca, Mg, K, Na, Fe, Al, Mn and Zn, in peat and mire vegetation in relation to the ecocline are described, with nitrogen and phosphorus being discussed in detail. In rich mires, P, N and K are the elements most highly concentrated into the mire vegetation, in poor mires the most concentrated elements are N and Mn. With regard to cycling K, Mn, Zn and Na appear to be more mobile than other elements. The amounts of soluble N and soluble Pare, greatest in the peat from ombrotrophic sites, and in both cases becomes lower along the gradient in the direction of rich fens.