Data from: Convergence in resource use efficiency across trees with differing hydraulic strategies in response to ecosystem precipitation manipulation

1. Plants are expected to respond to drought by maximizing the efficiency
of the most limiting resource, the water use efficiency (WUE), at the
expense of nitrogen and carbon use efficiencies (NUE and CUE). Therefore,
plants resource use efficiencies are viewed as indicators of species
drought tolerance. 2. We tested these predictions by measuring leaf-level
intrinsic WUE (WUEi, the ratio of net assimilation to stomatal
conductance), photosynthetic NUE (PNUE, the ratio of daily maximum net
assimilation to leaf nitrogen content) and leaf-scale CUE (approached by
the ratio of nighttime respiration to daytime net assimilation, Rd/An) in
piñon pine and juniper, two tree species that differ in drought tolerance
and vulnerability to drought-induced mortality. Variations in resource use
efficiency in the two species were measured in response to seasonal
drought and in response to an ecosystem-scale precipitation manipulation
experiment comprising three precipitation treatments: ambient, irrigation
(+30%) and partial rainfall exclusion (-45%). 3. Increasing water
limitation, either seasonally or across treatments, resulted in increased
WUE and decreased PNUE and CUE in both species. WUE, PNUE and CUE varied
more strongly in response to water limitation than across species and
converged to the same relationships against precipitation for piñon and
juniper. 4. Plasticity in WUE, PNUE and CUE in response to water
limitation was associated, in both species, with low carbon acquisition
during drought. Our results exhibited a convergence in resource use
efficiency across piñon and juniper which contradicts the paradigm that
resource use efficiencies are indicators of species drought tolerance and
ecological strategy.