Objective:
Building on the initial piñon-juniper drought experiment (see Historical Projects, Piñon-Juniper Drought Experiment 1.0), this project seeks to quantify links between plant physiological and defense strategies in mature trees and elucidate the underlying mechanisms of these responses over a range of drought conditions. This work is primarily supported by a separate NSF DEB award to Pockman.
Novelty:
This work seeks a mechanistic understanding of how tree drought stress affects the interactions among hydraulic function, carbohydrate availability, and chemical defense, including constitutive and induced defense components. The piñon-juniper system has been widely studied as a model of drought-induced plant mortality. This project addresses the paucity of information about the role of plant defensive responses during drought, particularly the existence of thresholds of drought causing diminished defense against bark beetles, their symbiotic fungi and other pathogens.
Design:
This experiment builds on the Piñon-Juniper Drought Experiment 1.0 by using the same basic design of large scale plots that intercept ambient precipitation and prevent it from reaching the plots in order to reduce plant-available water. Whereas the initial experiment imposed a replicated drought treatment that reduced ambient precipitation by ~45%, this experiment used the same infrastructure to impose different levels of drought along a gradient (45%, 70%, and 90%, in addition to a ‘legacy’ 45% plot established in 2010 during the first experiment).
Responses:
We measure plant water potential, micrometeorology, non-structural carbohydrates (NSC), enzyme activities, carbon isotope composition of NSCs, and emissions of volatile organic compounds to assess plant defensive responses across treatments.