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- Title
PROGRESSIVE NITROGEN LIMITATION OF ECOSYSTEM PROCESSES UNDER ELEVATED CO2 IN A WARM-TEMPERATE FOREST.
- Authors
Adrien C. Finzi; David J. P. Moore; Evan H. Delucia; John Lichter; Kirsten S. Hofmockel; Robert B. Jackson; Hyun-Seok Kim; Roser Matamala; Heather R. McCarthy; Ram Oren; Jeffrey S. Pippen; William H. Schlesinger
- Abstract
A hypothesis for progressive nitrogen limitation (PNL) proposes that net primary production (NPP) will decline through time in ecosystems subjected to a step-function increase in atmospheric CO2. The primary mechanism driving this response is a rapid rate Of N immobilization by plants and microbes under elevated CO2 that depletes soils of N, causing slower rates of N mineralization. Under this hypothesis, there is little long-term stimulation of NPP by elevated CO2 in the absence of exogenous inputs of N. We tested this hypothesis using data on the pools and fluxes of C and N in tree biomass, microbes, and soils from 1997 through 2002 collected at the Duke Forest free-air CO2 enrichment (FACE) experiment. Elevated CO2 stimulated NPP by 18–24% during the first six years of this experiment. Consistent with the hypothesis for PNL, significantly more N was immobilized in tree biomass and in the O horizon under elevated CO2. In contrast to the PNL hypothesis, microbial-N immobilization did not increase under elevated CO2, and although the rate of net N mineralization declined through time, the decline was not significantly more rapid under elevated CO2. Ecosystem C-to-N ratios widened more rapidly under elevated CO2 than ambient CO2 indicating a more rapid rate of C fixation per unit of N, a processes that could delay PNL in this ecosystem. Mass balance calculations demonstrated a large accrual of ecosystem N capital. Is PNL occurring in this ecosystem and will NPP decline to levels under ambient CO2? The answer depends on the relative strength of tree biomass and O-horizon N immobilization vs. widening C-to-N ratios and ecosystem-N accrual as processes that drive and delay PNL, respectively. Only direct observations through time will definitively answer this question.
- Subjects
NITROGEN; BIOTIC communities; PLANTS; BACTERIA; BIOMASS; BIOMINERALIZATION; FORESTS &; forestry; CARBON dioxide; ECOLOGY
- Publication
Ecology, 2006, Vol 87, Issue 1, p15
- ISSN
0012-9658
- Publication type
Article
- DOI
10.1890/04-1748