Carbon isotopic studies of assimilated and ecosystem respired CO₂ in a SE pine forest

Jeff Chanton, Florida State University

Co-investigator: Behzad Mortazavi, Florida State University

Abstract

1. Objectives. Our first objective in year 3 is to continue the determinations ofthe response ofthe δ¹³C signature of soil- (δCs), foliage-(δCf),and ecosystem-respired (δCr) CO₂ at the 80 year old Ameriflux site (Austin Carey Forest) near Gainesville, Florida to soil moisture, canopy vapor pressure deficit and temperature. Our second objective is to determine spatial variations in these parameters to contrast with our two primary seasonal sites, the Donaldsonville tract and the Austin Carey forest. We wish to determine the representativeness of our two primary sites in the overall forest mosaic.

2. Location. The research will take place in at and near to the two Ameriflux sites near Gainesville, Florida

3. Hypothesis 1. δCf, δCr and δCs will respond to canopy height/age and moisture deficits by exhibiting greater ¹³C enrichment. The degree of the response will be δCf> δCr > δCs. Younger shorter stands will respond to a greater degree to VPD than do older/taller stands.
Hypothesis 2: Isotopic variations in wax composition will co-vary with isotopic variations in leaf soluble sugars and leaf respiration with a temporal delay and damping which can be quantitatively related to wax turnover times and ecosystem respiration.

4. Approach
1. continue studies at the 80 year old Ameriflux sites quantifying as a function of VPD ¹³C of foliage (δCf), soil (δCs)and ecosystem (δCr) respired CO₂, δ¹³C of sugars.
2. Investigate gradients in tree-height/age in the vicinity of and including the two tower sites to determine the effect of tree age/height on of the δ¹³C of foliage respired CO₂, leaf sugars and leaf waxes and to determine if the response of these parameters to VPD varies as a function of tree height/age.

5. We will determine how climatic variables, operating by affecting Ll, and the balance between autotrophic and heterotrophic respiration affect the isotopic composition of ecosystem respired carbon dioxide (δCr). Data from our site indicate that δCr does not remain constant, and is ¹³C enriched during periods of low precipitation. For this project our deliverables will be the determination of the temporal variation at an 80 year old site and spatial variation of trees of δCr of trees of differing heights in areas surrounding the primary site.

Publications

Mortazavi, B., J. Chanton, and M.C. Smith. 2006. Influence of ¹³C-enriched foliage respired CO₂ on δ¹³C of ecosystem respired CO₂. Global Biogeochemical Cycles 20(3): GB3029 doi:10.1029/2005GB002650

Prater, J. L, Mortazavi, B., and J.P. Chanton. 2006. Diurnal variation of the ¹³C of pine needle respired CO₂ evolved in darkness.  Plant, Cell and Environment 29: 202-211.

Mortazavi, B., J. P. Chanton, J. L. Prater, A. Oishi, R. Oren and G. Katul. 2005. Temporal variability in ¹³C of respired CO₂ in a pine and a hardwood forest subject to similar climatic conditions. Ocelogia 142: 57-69.