Canopy N and P dynamics of a southeastern US pine forest under elevated CO 2

Adrien C. Finzi, Evan H. DeLucia, William H. Schlesinger

Research output: Contribution to journalArticle

Abstract

Forest production is strongly nutrient limited throughout the southeastern US. If nutrient limitations constrain plant acquisition of essential resources under elevated CO 2, reductions in the mass or nutrient content of forest canopies could constrain C assimilation from the atmosphere. We tested this idea by quantifying canopy biomass, foliar concentrations of N and P, and the total quantity of N and P in a loblolly pine (Pinus taeda) canopy subject to 4 years of free-air CO 2 enrichment. We also used N:P ratios to detect N versus P limitation to primary production under elevated CO 2. Canopy biomass was significantly higher under elevated CO 2 during the first 4 years of this experiment. Elevated CO 2 significantly reduced the concentration of N in loblolly pine foliage (5% relative to ambient CO 2) but not P. Despite the slight reduction foliage N concentrations, there were significant increases in canopy N and P contents under elevated CO 2. Foliar N:P ratios were not altered by elevated CO 2 and were within a range suggesting forest production is N limited not P limited. Despite the clear limitation of NPP by N under ambient and elevated CO 2 at this site, there is no evidence that the mass of N or P in the canopy is declining through the first 4 years of CO 2 fumigation. As a consequence, whole-canopy C assimilation is strongly stimulated by elevated CO 2 making this forest a larger net C sink under elevated CO 2 than under ambient CO 2. We discuss the potential for future decreases in canopy nutrient content as a result of limited changes in the size of the plant-available pools of N under elevated CO 2.

Original languageEnglish (US)
Pages (from-to)363-378
Number of pages16
JournalBiogeochemistry
Volume69
Issue number3
DOIs
StatePublished - Jul 1 2004

Keywords

  • Elevated CO
  • Foliar N:P ratios
  • Nitrogen
  • Phosphorus

ASJC Scopus subject areas

  • Environmental Chemistry
  • Water Science and Technology
  • Earth-Surface Processes

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