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The aim of the study was to explore the effects of climate-induced soil properties on nitrogen (N) transformation and N2O emissions in the tropical region.

Soil samples were collected from the soils developed from granite and covered with secondary forest vegetation along with the aridity gradient in the Hainan Islands, China, in which the annual mean temperature ranged from 24 to 25 A degrees C, but the annual precipitation from 1,000 to 2,166 mm, and the annual evaporation from 1,861 to 2,409 mm within about 180 km. The gross of N transformation rates and N2O emissions in the soils were determined by employing N-15 tracing methods at laboratory incubation under conditions of 60 % WHC and 25 A degrees C.

The gross rate of mineralization and turnover rate of soil organic N increased significantly (P < 0.05 for both), but net mineralization rate did not differ significantly with the increase of aridity index (Di) (P > 0.05). Gross and net rate of nitrification increased significantly (P < 0.05 for both), while cumulative N2O emissions over the incubation period did not differ significantly along the aridity gradient (P > 0.05). Statistical analysis showed that soil pH, which was correlated significantly with Di, was correlated significantly with the gross rate of N mineralization, turnover rate of soil organic N, gross nitrification, and the ratio of N2O in nitrification products.

The investigation indicated that the climate-induced soil properties had significant effects on the gross and net N transformation rates, but not on net mineralization and N2O emissions in the tropical secondary forests in the Hainan Island.