Nitrogen mineralization and nitrification in rainforests of contrasting nutrient status and physiognomic structure near Lake Eacham, northeast Queensland

Abstract

AbstractNitrogen mineralization and nitrification were measured using in situ incubations for 12 periods of 1 month in a structurally complex rainforest with basaltic soil, and an adjacent structurally simple rainforest with less fertile soil formed on metamorphic rock. The study was undertaken near Lake Eacham on the Atherton Tableland in northeast Queensland.Cumulative nitrogen mineralization for 1 year did not differ between forests. It amounted to 265 ± 13 μg N g‐1 oven dry soil at the upper position (0–7.5 cm) and 122 ± 11 μg N g‐1 oven dry soil at the lower position (7.5–15 cm; mean ± s.e. for pooled data). Rates were highest during the wet season but were not strongly correlated with moisture content or temperature.Relative nitrification (cumulative nitrate‐nitrogen production expressed as a percentage of cumulative nitrogen mineralization) at the upper position was significantly higher in the complex than the simple forest (100% c.f. 88%). At the lower position it amounted to 100% for cumulative data in both forests. Nitrate was the dominant form of inorganic nitrogen in the complex forest but in the simple forest nitrate and ammonium were of similar importance.The association between forest physiognomic structure and nutrient status at Lake Eacham represents a more general pattern in rainforests of northeast Queensland and further study is needed to ascertain whether results from this study apply more generally.