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Forest calcium depletion and biotic retention along a soil nitrogen gradient

Ecological Applications

By:
, , , , , , and
DOI: 10.1890/12-2204.1

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Abstract

High nitrogen (N) accumulation in terrestrial ecosystems can shift patterns of nutrient limitation and deficiency beyond N toward other nutrients, most notably phosphorus (P) and base cations (calcium [Ca], magnesium [Mg], and potassium [K]). We examined how naturally high N accumulation from a legacy of symbiotic N fixation shaped P and base cation cycling across a gradient of nine temperate conifer forests in the Oregon Coast Range. We were particularly interested in whether long-term legacies of symbiotic N fixation promoted coupled N and organic P accumulation in soils, and whether biotic demands by non-fixing vegetation could conserve ecosystem base cations as N accumulated. Total soil N (0–100 cm) pools increased nearly threefold across the N gradient, leading to increased nitrate leaching, declines in soil pH from 5.8 to 4.2, 10-fold declines in soil exchangeable Ca, Mg, and K, and increased mobilization of aluminum. These results suggest that long-term N enrichment had acidified soils and depleted much of the readily weatherable base cation pool. Soil organic P increased with both soil N and C across the gradient, but soil inorganic P, biomass P, and P leaching loss did not vary with N, implying that historic symbiotic N fixation promoted soil organic P accumulation and P sufficiency for non-fixers. Even though soil pools of Ca, Mg, and K all declined as soil N increased, only Ca declined in biomass pools, suggesting the emergence of Ca deficiency at high N. Biotic conservation and tight recycling of Ca increased in response to whole-ecosystem Ca depletion, as indicated by preferential accumulation of Ca in biomass and surface soil. Our findings support a hierarchical model of coupled N–Ca cycling under long-term soil N enrichment, whereby ecosystem-level N saturation and nitrate leaching deplete readily available soil Ca, stimulating biotic Ca conservation as overall supply diminishes. We conclude that a legacy of biological N fixation can increase N and P accumulation in soil organic matter to the point that neither nutrient is limiting to subsequent non-fixers, while also resulting in natural N saturation that intensifies base cation depletion and deficiency.

Geospatial Extents

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Forest calcium depletion and biotic retention along a soil nitrogen gradient
Series title:
Ecological Applications
DOI:
10.1890/12-2204.1
Volume
23
Issue:
8
Year Published:
2013
Language:
English
Publisher:
Ecological Society of America
Contributing office(s):
Forest and Rangeland Ecosystem Science Center
Description:
15 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Ecological Applications
First page:
1947
Last page:
1961
Number of Pages:
15
Country:
United States
State:
Oregon
Other Geospatial:
Oregon Coast Range