Leaf trait measurements
The fully expanded leaf selected for transpiration measurements (section above) was afterwards collected, photographed for calculation of area using ImageJ (Schneider 2012) and placed in weighed glass tubes. Fresh weight was first recorded and its water extracted according to Vendramini and Sternberg Lda (2007) for measurements of δ18OLW. The dried leaf material was weighed to calculate leaf water content (LWC) and leaf dry mass per area (LMA). LWC was calculated as the difference between fresh and dry leaf weight per area and LMA was calculated as dry leaf weight per leaf area.
Root crowns were collected and placed in a separate glass tube for water extraction (Vendramini & Sternberg Lda 2007) and oxygen isotope analysis, so that source water was characterized for each plant to calculate leaf water oxygen isotope enrichment (Δ18OLW). Vapor from the growth chamber was collected every 30 min during transpiration measurements. The vapor was sealed in 5 L inert foil gas sampling bags (Supelco Analytical #30228-U; Bellefonte, PA) that restrict exchange of water vapor or CO2 exchange with ambient air, and after collection the vapor samples were measured immediately (details below).