Girdling experiments
To test for an effect of reduced phloem transport during drought on
foliage hormone levels, prior to drought a single, large branch on three
individuals was girdled. Branches were girdled by carefully removing two
to three cm of periderm just above the intersection of a side branch and
the main, leading stem. Once periderm was removed a hydrogel was applied
to the xylem (Tensive, Parker Labs, Fairfield, NJ, USA). Samples from
girdled and non-girdled branches were harvested concurrently to
determine Ψl using a Scholander pressure chamber and to
collect a subsample of tissue for hormone quantification.