COS 39-4 - Physiological response of drought stressed piñon pine and juniper trees to large precipitation events following 5+ years of experimentally imposed and naturally occurring drought

Wednesday, August 10, 2016: 9:00 AM
305, Ft Lauderdale Convention Center
Robert E. Pangle1, Jean Marc Limousin2, Patrick Hudson1, Amanda L. Boutz1, Nate Gehres1, Nate McDowell3 and Will Pockman1, (1)Department of Biology, University of New Mexico, Albuquerque, NM, (2)CNRS, Centre d'Ecologie Fonctionnelle et Evolutive CEFE, Montpellier, France, (3)Pacific Northwest National Laboratory, Richland, WA
Background/Question/Methods

In recent years, the occurrence and severity of drought events in many semi-arid systems has been increasing.  Prolonged drought can lead to tree mortality and canopy dieback, and stressed trees exhibit varying degrees of physiological recovery following drought cessation.  A decline in plant hydraulic conductance and canopy gas-exchange is often observed in drought stressed trees, and the recovery of hydraulic function post-drought is critical for surviving trees to take full advantage of favorable growth conditions.  Here, we report on the short-term physiological recovery of drought stressed piñon pine (Pinus edulis) and juniper (Juniperus monosperma) trees following large precipitation events (90+ mm) that fully alleviated plant water stress.  This study is unique, in that our study trees had been exposed to 5+ years of experimentally imposed and naturally occurring drought preceding the precipitation events. To assess short-term physiological recovery post-drought, we examined multiple variables; including whole plant hydraulic conductance (K), plant leaf water potential (ΨPD), and soil water availability (VWC).  Our objectives were; 1) to assess the hydraulic recovery of experimentally droughted trees compared to ambient control trees, 2) assess species specific patterns of post-drought recovery, and 3) assess if juniper recovery varied with soil depth.

Results/Conclusions

Following a precipitation anomaly (90 mm day-1) in summer 2012, water stress was alleviated with significant increases in VWC and ΨPD observed across the study site, regardless of pre-event drought severity (i.e., drought treatment versus ambient control).  Pre-event (5+ year period), droughted pine and juniper both exhibited significantly lower average plant K as compared to ambient control trees.  Post-event, K in droughted pine increased (to 0.6 mol m-2 s-1 MPa-1), but did not recover to levels observed in the control pine (1.1 mol m-2 s-1 MPa-1).  In contrast, recovery of K in droughted juniper varied depending on soil depth.  In plots with deeper soils (>1m), K of droughted juniper recovered to levels observed in ambient juniper (~1.0 mol m-2 s-1 MPa-1), while K of droughted juniper growing in shallow soil (<1m) was lower than ambient juniper post-event (0.45 versus 0.75 mol m-2 s-1 MPa-1 respectively).  Our results indicate that severe drought induces hydraulic & physiological impairment in pine and shallow rooted juniper that persists post drought. Trees with reduced plant K are unable to take full advantage of increased VWC, which is detrimental to tree recovery in a semiarid system where trees often rely on short-term pulses in soil VWC.