Nitrogenase activity in the papyrus swamps of Lake Naivasha, Kenya

Abstract

Nitrogenase activity (acetylene reduction activity) was found to occur universally in the Cyperus papyrus swamp in Lake Naivasha. Low rates of acetylene reduction activity (0.9–104.9 nmol C2H4 g d.wt. roots-1 h-1) were associated with excised roots of C. papyrus but higher rates of activity (89.0–280.4 nmol C2H4 g d.wt. roots-1 h-1) were associated with intact root systems of the plant. It was estimated that nitrogen fixation associated with young roots alone could supply about 26% of the nitrogen requirements of growing papyrus plants. Acetylene reduction activity in the lake bottom sediments was generally low and associated with adjacent papyrus stands. Plate counts of putative aerobic and facultatively anaerobic N2-fixing bacteria associated with papyrus roots showed the presence of high numbers of diazotrophs (5.4 × 106 CFU g d.wt. roots-1). Fewer numbers of N2-fixing bacteria were detected in the sediments (1.9 × 103-3.2 × 104 CFU g d.wt. sediment-1).