Gross rates of nitrogen transformation in soils of a global biodiversity hotspot (Western Ghats, India)

Abstract

AbstractBackground: Being one of the important nutrients required by plants during photosynthesis, nitrogen (N) exerts a significant control on primary productivity and carbon dioxide sequestration. Therefore, it is essential to quantify the rates of N cycling processes, such as gross N mineralization and nitrification, to understand the flow and availability of N in different ecosystems. Lack of such data in tropical regions, particularly the Indian subcontinent, has constrained our understanding of N dynamics in soils of the subcontinent.Aims: Here, we report the results of gross N transformation rates from the hot and humid tropical forest soils of the Western Ghats, one of the global biodiversity hotspots located in India.Results: The experiments conducted using the 15N isotope dilution technique showed higher average gross N mineralization (2.6 ± 1.1 mg N kg−1 d−1) and gross nitrification (1.7 ± 1.1 mg N kg−1 d−1) rates in the top soil layers (0–20 cm), which decreased significantly with depth (20–40 cm) indicating potential for higher microbial activity in the top soils. The overall consumption rate of mineral N exceeded its production rate with higher consumption of ammonium () than nitrate () suggesting as a preferred N source for microbes. The consumption of was higher through immobilization than nitrification indicating active N conservation mechanism and an efficient microbial adaptation.Conclusion: Despite high rates of consumption, accumulation of and in soils of the Western Ghats suggested additional sources of mineral N other than internal recycling of N. Long residence time of and in soils implied longer availability of unutilized mineral N leading to high soil acidity and potential for loss of N through leaching and denitrification.