The role of Carbon depletion in conifer physiological resistance to drought
Abstract
Identifying how trees succumb to drought and which physiological traits influence drought resistance is an on-going challenge in western forests. During drought, theory predicts that trees with high hydraulic safety (resistance to cavitation under drought stress) will survive. We leveraged the California "hot drought" of 2012-2016—more severe than any observed in the previous 1200 years—as a natural experiment to assess how living and dead trees differed in growth and wood anatomy relative to climate. We sampled living and dead Pinus ponderosa and P. jeffreyi in multiple stands that experienced extensive drought-induced mortality in the Sierra Nevada. Xylem cell "thickness-to-span" (T:S)—the ratio of tracheid wall thickness to tracheid diameter—was higher in drought-killed trees than living trees. Annual growth in living trees increased slightly or stayed constant during and following the drought, while dead trees rapidly decreased growth prior to mortality. However, trees that eventually died grew much faster on average than trees that survived. We then tested the hypothesis that high hydraulic safety through xylem lignification comes at a greater carbon (C) expense, which may limit other C-intensive processes such as pest defense and radial growth. We measured total lignin and C concentrations in annual rings. Dead trees were found to have higher average lignin concentrations than living trees, and varied annually in lignin concentration more than living trees. Trees in the Sierra Nevada were subjected to interactive stresses of bark beetle and drought, representing potentially competing C sinks. Results demonstrate the C budget implications of drought defense and suggest that drought-induced xylem cell wall thickening may induce a positive feedback loop of C limitation under drought and pest stress.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B44F..13L
- Keywords:
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- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCES;
- 0466 Modeling;
- BIOGEOSCIENCES;
- 0476 Plant ecology;
- BIOGEOSCIENCES