| Popis: |
The C 2 H 2 reduction method was used on eight occasions between January 1983 and January 1984 to measure the effects of adding superphosphate (60 kg P ha −1 applied in September 1979) and of prescribed burning (May 1981) on nitrogenase activity in the forest floor of an 18 year old Pinus elliottii plantation in southeast Queensland. Averaged over sampling days, superphosphate increased nitrogenase activity in the forest floor 4.0-fold in the unburnt plots and 2.0-fold in burnt plots. In the absence of superphosphate, burning increased activity 3-fold but in plots receiving superphosphate a response to burning was seldom evident. The responses were attributed to increased nutrient availability. Nitrogenase activity was highest in the F1 layer (weathered needles in the centre of the forest floor) and lowest in the L layer (recently fallen needles). Moisture content has a strong effect on forest floor nitrogenase activity and, in laboratory dried material, activity increased most rapidly for moisture contents between 80 and 170%. Mean nitrogenase activity in the forest floor on individual sampling days ranged from 3 nmol C 2 H 4 g −1 (L layer, control treatment) to 233 nmol C 2 H 4 day −1 (F1 layer, combined refertilized and burnt treatment). Activity was also detected in dead wood, female cones, thinning debris, soil (0–5 cm) and roots, but was negligible in bark and green needles. |
