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Retention and hydrolysable fraction of atmospherically deposited nitrogen in two contrasting forest soils in Switzerland

2010; Wiley; Volume: 61; Issue: 2 Linguagem: Inglês

10.1111/j.1365-2389.2010.01226.x

1365-2389

I. Morier, Patrick Schleppi, Matthias Saurer, Isabelle Providoli, Claire Guenat,

Soil and Water Nutrient Dynamics

Nitrogen (N) from atmospheric deposition has been shown to be mainly retained in the organic soil layers of temperate forest ecosystems, but the mechanisms and the physico‐chemical fractions involved are still poorly defined. We performed a hot‐acid hydrolysis on 15 N‐labelled soil samples collected 1 week, 3 months and 1 year following a single in situ application of either 15 NO 3 − or 15 NH 4 + in two montane forest ecosystems in Switzerland: Grandvillard (beech forest on a calcareous, well‐drained soil, 650 m above sea level) and Alptal (spruce forest on hydromorphic soil, 1200 m above sea level). After 15 NH 4 + application, recovery rates in the soil were smaller in Alptal than in Grandvillard through a large rate of absorption by mosses. At both sites, the organic soil layers retained most of the tracers at all three sampling times between 1 week and 1 year. In Grandvillard, the hydrolysable fraction (hydrolysable N : total N) of 15 N was on average 79% and thus similar to the hydrolysable fraction of native N. This similarity is probably because of the rapid incorporation of N into organic molecules, followed by stabilization of the recalcitrant N pool through organo‐mineral bonds with soil minerals. In Alptal, the 15 N hydrolysable fraction was greater than that of native N, particularly after 15 NH 4 + application ( 15 N, 84%; native N, 72%). At both sites, 15 N and the fraction of hydrolysable native N remained constant between 1 week and 1 year. This shows that both the recalcitrant and the hydrolysable pools are stable in the mid‐ to long‐term. We present arguments indicating that biological recycling through microbes and plants contributes to the stability of the hydrolysable N fraction.