Nitrification mineralisation and inorganic-N uptakein evergreen forests of the central Himalayas

Abstract

Nitrogen mineralisation and available nitrogen (NO 3 – + NH 4 +) in two evergreen forests species, viz. Quercus leucotrichophora and Pinus roxburghii, were examined. The plant available N ranged from 7.7–35.8 μg·g –1·m –1 with maximum values in March and minimum in November. The trend for N-mineralisation was opposite to that of the size of the available N-pool. N-Mineralisation rates ranged from 1.7–30.3 μg·g –1·m –1 within an annual cycle. Inorganic-N uptake was calculated for each incubated period, and for an entire year showed that in an oak forest site, nitrate-N was the dominant form of mineral nitrogen taken up by plants from soil. However, in a chir pine forest, nitrate-N and ammonium-N are equally taken up by plants from the soil. In both oak and pine forest sites, the nitrate-N uptake was maximum in the month of July and ranged between 2.4–11 μg·g –1·m –1 in the pine forest site and from 0–25 μg·g –1·m –1 in the oak forest site. In addition, ammonium-N varied from 0–12 μg·g –1·m –1 in the pine forest site and from 1–20 μg·g –1·m –1 in the oak forest site. N-Mineralisation was greater in N-rich forests and was moisture (soil) dependent and inversely related to bulk density.