PUB - Publikationen an der Universität Bielefeld

In this study we measured delta C-13 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 delta C-13 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 delta C-13 of water-soluble organic matter pools along the plant axis with progressive depletion in delta C-13 from the canopy to the trunk (similar to 6.5% depletion in A. longifolia and similar to 0.8% depletion in P. pinaster). Regardless of these fractionation effects, phloem sap delta C-13 in both terminal branches and the main stem correlated well with environmental parameters driving photosynthesis for both species, indicating that phloem sap delta C-13 has potential as an integrative tracer of changes in canopy carbon discrimination (Delta C-13). Furthermore, we illustrate that a simple model based on sap flow estimated canopy stomatal conductance (G(S)) and phloem sap delta C-13 measurements has significant potential as a tool for estimating canopy-level carbon assimilation rates.