On the use of phloem sap δ¹³C as an indicator of canopy carbon discrimination.
In this study we measured δ¹³C in various carbon pools along the basipetal transport pathway in co-occurring Pinus pinaster and Acacia longifolia trees under Mediterranean climate conditions in the field. Overall, species differences in photosynthetic discrimination resulted in more enriched δ¹³C values in the water-conserving overstory P. pinaster relative to the water-spending understory invasive A. longifolia. Post-photosynthetic fractionation effects resulted in differences in δ¹³C of water-soluble organic matter pools along the plant axis with progressive depletion in δ¹³C from the canopy to the trunk (∼6.5‰ depletion in A. longifolia and ∼0.8‰ depletion in P. pinaster). Regardless of these fractionation effects, phloem sap δ¹³C in both terminal branches and the main stem correlated well with environmental parameters driving photosynthesis for both species, indicating that phloem sap δ¹³C has potential as an integrative tracer of changes in canopy carbon discrimination (Δ¹³C). Furthermore, we illustrate that a simple model based on sap flow estimated canopy stomatal conductance (G(S)) and phloem sap δ¹³C measurements has significant potential as a tool for estimating canopy-level carbon assimilation rates.
Exp. and Systems Ecology, University of Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany. katherine.grieve@uni-bielefeld.de
Katherine G
KG
Rascher
Cristina
C
Máguas
Christiane
C
Werner
D000045:Acacia / Q000378:metabolism*; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide; D002247:Carbon Isotopes; D002940:Circadian Rhythm; D002980:Climate; D017753:Ecosystem; D052585:Phloem / Q000502:physiology*; D028223:Pinus / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D018526:Plant Transpiration; D012621:Seasons; D014867:Water
D002247:Carbon Isotopes; D014867:Water; D002245:Carbon Dioxide; D002244:Carbon