Nitrogen States in Plant Ecosystems: A Viewpoint

Terrestrial ecosystems are considered to be in only two possible states: N unsaturated or N saturated. This view lacks rigour and has led to three differing concepts of N saturation: (1) a continuum of changes in N states and processes; (2) a threshold point, when N output increases; and (3) any equ...

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Bibliographic Details
Published in:Annals of botany 2000-12, Vol.86 (6), p.1161-1167
Main Authors: Cannell, M.G.R., Thornley, J.H.M.
Format: Article
Language:English
Subjects:
deposition
Ecological balance
Ecosystem models
Ecosystems
forest
Forest ecology
Forest ecosystems
leaching
Marine ecosystems
nitrification
Nitrogen
Nitrogen saturation
Nitrogen saturation, deposition, leaching, nitrification, plant ecosystems, forest
plant ecosystems
Plants
Soil ecology
Terrestrial ecosystems
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Summary:Terrestrial ecosystems are considered to be in only two possible states: N unsaturated or N saturated. This view lacks rigour and has led to three differing concepts of N saturation: (1) a continuum of changes in N states and processes; (2) a threshold point, when N output increases; and (3) any equilibrium state, when N output equals N input. A simple model of ecosystem N content, input and output is used to point out that, strictly, there are four possible N states of ecosystems: (1) at equilibrium, but N unsaturated and N-limited, so that they will respond to additional N input with increased N accumulation; (2) not at equilibrium and accumulating N, either in response to additional N input, or more commonly in nature, when recovering from fire, other disturbance or unfavourable conditions; (3) at equilibrium but truly N saturated and not N-limited, so that any additional N input is matched by equal N output; and (4) not at equilibrium and losing N because of disturbance or soil changes induced by N addition itself or other factors. Most natural ecosystems are, for most of the time, in one of the two non-equilibrium states, especially in short-term N-addition experiments. It is not meaningful to regard them as being either N saturated or N-limited.
ISSN:0305-7364
1095-8290
DOI:10.1006/anbo.2000.1286