Physiological differences among species determine drought tolerance and
stomatal regulation of water loss, thus feed back to the vegetation
structure of the ecosystem by determining growth and survival under
different precipitation regimes. We have manipulated precipitation inputs
in black grama grassland, creosote shrubland and piñon-juniper woodland at
the Sevilleta LTER to understand aspects of these interactions. Rainout
shelters have been used to impose extended drought by diverting ambient
precipitation while overhead sprinkler systems have been employed to
increase water inputs on adjacent plots. In each case, intensive
measurements of plant water potentials have been conducted on Bouteloua
eriopoda, Larrea tridentata, Pinus edulis and Juniperus monosperma.

Results/Conclusions

Manipulating rainfall patterns were evident in the water potential
measurements across all four ecotones but differed among species. After 5
years the drought experiment ended at the grass and shrubland plots, but
ongoing measurements of post-drought recovery is taking place in those
plots. Precipitation is still being added to the rainfall addition plots
at the grassland and shrubland sites. Rainfall manipulation is also still
ongoing in the piñon-juniper woodland.