Premium
Modelling environmental controls on ecosystem photosynthesis and the carbon isotope composition of ecosystem‐respired CO 2 in a coastal Douglas‐fir forest
Author(s) -
CAI TIEBO,
FLANAGAN LAWRENCE B.,
JASSAL RACHHPAL S.,
BLACK T. ANDREW
Publication year - 2008
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.2008.01773.x
Subject(s) - photosynthesis , ecosystem , environmental science , ecosystem respiration , stomatal conductance , isotopes of carbon , stable isotope ratio , eddy covariance , δ13c , carbon cycle , atmospheric sciences , vapour pressure deficit , carbon dioxide , botany , environmental chemistry , chemistry , ecology , transpiration , biology , total organic carbon , geology , physics , quantum mechanics
We developed and applied an ecosystem‐scale model that calculated leaf CO 2 assimilation, stomatal conductance, chloroplast CO 2 concentration and the carbon isotope composition of carbohydrate formed during photosynthesis separately for sunlit and shaded leaves within multiple canopy layers. The ecosystem photosynthesis model was validated by comparison to leaf‐level gas exchange measurements and estimates of ecosystem‐scale photosynthesis from eddy covariance measurements made in a coastal Douglas‐fir forest on Vancouver Island. A good agreement was also observed between modelled and measured δ 13 C values of ecosystem‐respired CO 2 ( δ R ). The modelled δ R values showed strong responses to variation in photosynthetic photon flux density (PPFD), air temperature, vapour pressure deficit (VPD) and available soil moisture in a manner consistent with leaf‐level studies of photosynthetic 13 C discrimination. Sensitivity tests were conducted to evaluate the effect of (1) changes in the lag between the time of CO 2 fixation and the conversion of organic matter back to CO 2 ; (2) shifts in the proportion of autotrophic and heterotrophic respiration; (3) isotope fractionation during respiration; and (4) environmentally induced changes in mesophyll conductance, on modelled δ R values. Our results indicated that δ R is a good proxy for canopy‐level C c / C a and 13 C discrimination during photosynthetic gas exchange, and therefore has several applications in ecosystem physiology.