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

Nitrogen mineralisation and available nitrogen (NO3– + NH4+) 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.