Hydraulic lift and water acquisition from rock fractures
In addition to determining the isotopic fingerprints in tree wood and
water sources, we implemented a second labelling study, to examine the
capability of tree species to explore rock fractures and vertically
re-distribute water to the soil surface. We injected labeled water (δD =
-88.2‰, δ18O = -11.8‰, natural abundance) in rock
fractures next to either oak or pine trees as target plant with a
neighboring tree of the respective other species
(oaktarget → pineneighbor,
pinetarget → oakneighbor) considering
three distance ranges (0-2, 2-4 and 4-6 m) between tree pairs (total
number of trees = 24 targets and 24 neighbors). For the labelled water
injection, we inserted a 1.5 cm diameter hose 30 cm down a rock fracture
within 30-50 cm of the target tree. With a syringe (750 ml), labeled
water (δD = 485.1‰; 5.5 times enriched compared to natural abundance of
deuterium) was slowly injected through the hose to avoid contamination
of the surface soil with labeled water. We tracked the
D2O tracer by collecting 4 to 6 twigs from different
places of the crown from both the target and neighboring tree, and soil
samples next (minimum distance 50 cm) to both trees (0-15 cm depth).
After the D2O injection (day 0), twigs and soil cores
(n = 4 ) were collected at noon for the following 10 days.