Factors affecting nitrogenase activity associated with marsh grasses and their soils from eutrophic lakes

Abstract

The acetylene reduction activity (ARA) of soil-plant cores and intact, soil-free plant-root systems was used to study the influence of soil moisture content, diurnal cycles of temperature and light, and inorganic N and P on the nitrogenase activity (AR) associated with Phalaris arundinacea L. and Phragmites australis (Cav.) Trin. from two eutrophic lakes (lochs), Balgavies and Forfar. A positive correlation ( r = 0.81, n = 26) was established between AR and soil moisture content in individual soil-plant cores of Phalaris from Forfar Loch. Nitrogenase activity, soil moisture and NO 2 −-N increased with decreasing distance from lake water in Balgavies Loch. Diurnal fluctuations in AR, probably attributable to a combined effect of soil temperature and illumination changes, were observed under field conditions for Phalaris and Phragmites. Under laboratory conditions, the shading and cutting of Phalaris shoots did not inhibit ARA, which suggested that new photosynthates did not necessarily supply substrate for activity in the short term. Partial and temporary inhibition of ARA was obtained in dissected soil-plant cores after a single application of NH 4 +-N and NO 3 −-N (350 μg N g −1 fresh weight). At concentrations equivalent to 300 μg P g −1 fresh weight of Phalaris cores, PO 4 3−-P also caused partial and temporary inhibition of ARA of soil-free plant-root systems, but stimulated activity in intact simulated in situ systems.