科研之友
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摘要
Human activities have fundamentally changed global nitrogen (N) cycling, leading to elevated N deposition in most parts of the world. The fate of deposited N, whether being retained to sustain plant growth or causing ecosystem N saturation, is critical to the global carbon (C) cycling and local environment. In a short-term laboratory experiment, we used N-15-labeled NH4+ and NO3- to study the fate of N inputs in forest soils and what regulates N retention. Soils with a wide range of organic matter content and other attributes were collected from a 70-year-old plantation containing monotypic stands of Norway spruce (Picea abies), red pine (Pinus resinosa), sugar maple (Acer saccharum), and red oak (Quercus rubra), and separated into 0-5 cm and 5-15 cm layers. Nitrogen added to the soil was either immediately extracted (Time 0:T0) with K2SO4 solution, or incubated for 7 d (T7) and then extracted. Retention of N-15 into the non-extractable soil pool at TO was limited; but after the 7-d incubation, between 20 and 70% of the (NH4+)-N-15 was retained. Nitrification transformed on average 50% of the (NH4+)-N-15 into (NO3-)-N-15 during the incubation while retention of (NO3-)-N-15 at T7 remained low (7.40 +/- 1.08%). Retention of (NH4+)-N-15 into non-extractable soil at T7 was positively correlated to the percentage of soil organic matter (SOM) (r(2) = 0.323, P<0.001), and was significantly higher (P<0.001) in the high-SOM 0-5 cm layer than in the low-SOM 5-15 cm layer. Conversion of (NH4+)-N-15 to (NO3-)-N-15 during incubation significantly reduced the (NH4+)-N-15. retention (P<0.001). Our results suggest that the variations of SOM and other soil attributes play strong roles in the retention of newly deposited inorganic N and could affect forest ecosystem responses to chronic N deposition.
- 出版日期2011-2-1
