Publication

Journal	Plant, Cell & Environment
Volume (Issue)	38
Page(s)	2551 - 2565
Title of proceedings	Plant, Cell & Environment
DOI	10.1111/pce.12568

The Peclet correction is often used to predict leaf evapora- tive enrichment and requires an estimate of effective path length (L). Studies to estimate L in conifer needles have produced unexpected patterns based on Peclet theory and leaf anatomy. We exposed seedlings of six conifer species to different vapour pressure deficits (VPD) in controlled climate chambers to produce steady-state leaf water enrich- ment (in 18O). We measured leaf gas exchange, stable oxygen isotopic composition (δ18O) of input and plant waters as well as leaf anatomical characteristics. Variation in bulk needle water δ18O was strongly related to VPD. Conifer needles had large amounts of water within the vascular strand that was potentially unenriched (up to 40%). Both standard Craig– Gordon and Peclet models failed to accurately predict conifer leaf water δ18O without taking into consideration the unenriched water in the vascular strand and variable L. Although L was linearly related to mesophyll thickness, large within-species variation prevented the development of gen- eralizations that could allow a broader use of the Peclet effect in predictive models. Our results point to the impor- tance of within needle water pools and isolating mechanisms that need further investigation in order to integrate Peclet corrections with ‘two compartment’ leaf water concepts.