Use of principal component analysis to assess factors controlling net N mineralization in deciduous and coniferous forest soils

Abstract

Net N mineralization was studied in three different forest sites (Belgium): a mixed deciduous forest with oak (Quercus robur L. and Quercus rubra L.) and birch (Betula pendula Roth) as dominant species, a deciduous stand of silver birch (Betula pendula) and a coniferous stand of Corsican pine (Pinus nigra ssp. Laricio). The organic (F + H) layer and mineral soil at different depths (0–10, 10–20 and 20–30 cm) were sampled at three locations in the mixed deciduous forest (GE, GF1, GF2), at one location in the silver birch stand (SB) and one in the Corsican pine stand (CP). All samples were incubated over 10 weeks under controlled temperature and moisture conditions. The net N mineralization rates in the organic and upper mineral layer (0–10 cm) were found to be significantly different from the other layers and accounted for 66–95% of the total mineralization over the first 30 cm. Net N mineralization rates in the organic layer ranged from 4.2 to 27.3 mg N m–2 day–1. Net N mineralization and nitrification rates were positively correlated. For the mineral soil, net N mineralization rates decreased with depth and the upper 10 cm showed significantly higher rates, ranging from 8.9 to 33.5 mg N m–2 day–1. The rates of the 10–20 cm and 20–30 cm sublayers were similar, ranging from 1.2 to 7.4 mg N m–2 day–1. The net N mineralization rates for the total mineral layer (0–30 cm) ranged from 17.4 mg N m–2 day–1 (SB) to 36.1 mg N m–2 day–1 (CP). Both from PCA and multiple regression analysis, we could conclude that net N mineralization rates were closely related to the initial mineral N content (Ninitial). Furthermore, significant correlations were observed between the net N mineralization rate, the total carbon (TC) and NH4+-N content for the mineral layers and between net N mineralization rate, total nitrogen (TN), hemicellulose content and C/N for the organic layers.