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).