Effects of Precipitation Manipulation on Carbohydrate Dynamics and Mortality in a Piñon-Juniper Woodland

摘要

Drought induced forest mortality is an accelerating global problem with far-reaching consequences,rnyet mortality mechanisms remain poorly understood. Depletion of non-structural carbohydratern(NSC) stores has been implicated as a major factor in drought-induced mortality, but experimentalrnfield tests are rare. We conducted an ecosystem-scale precipitation manipulation experimentrnand evaluated foliar and twig NSC dynamics of two co-occurring conifers with different waterrnregulation strategies; the drought-avoiding piñon pine (Pinus edulis) and drought-tolerant one-seedrnjuniper (Juniperus monosperma). Experimental drought decreased foliar starch in dying trees of bothrnspecies and increased allocation to glucose and fructose in juniper, consistent with osmoregulationrnrequirements. For both species, average foliar starch concentration between drought treatmentrnonset and date of recorded mortality was a good predictor (R2 = 0.77) of the duration of droughtsurvival.rnThese results along with observations of limitations to photosynthesis and growthrnimplicate carbon starvation as an important process during mortality of these two conifer species.