OOS 36-6
Recovery from drought -induced embolism and mortality of multiple species across a rainfall gradient, from rainforest to semi-arid

Thursday, August 14, 2014: 9:50 AM
304/305, Sacramento Convention Center
Melanie J.B. Zeppel, Department of Biology, Centre for Climate Futures, Macquarie University, North Ryde NSW 2109, Australia
Henry D. Adams, Earth and Environmental Sciences, Los Alamos National Laboratory, Los Alamos, NM
Patrick J. Hudson, Biology, University of New Mexico- Albuquerque, Albuquerque, NM
William R. L. Anderegg, Ecology and Evolutionary Biology, Princeton University, Princeton, NJ
Derek Eamus, Department of Environmental Science, University of Technology, Sydney, Sydney, Australia
David T. Tissue, Hawkesbury Institute for the Environment, University of Western Sydney, Richmond NSW, Australia
Background/Question/Methods

Long-term and intense droughts are characteristic of many ecosystems. Drought can lead to embolism of xylem, which if not refilled or regrown can accumulate to lethal levels. Greater understanding of plant traits associated with drought resilience, such as xylem refilling, may increase predictability of species susceptibility to drought-induced mortality in the future. Xylem refilling is an important drought response, whereby trees that can refill easily may experience cavitation more frequently compared with trees that cannot refill, which may avoid or minimize cavitation. These distinctions shed insight into what types of species are lethal to what types of species.Interestingly, many plants exhibit significant night-time stomatal conductance, which may contribute to refilling of xylem embolism. To date, we are unaware of other studies that have compared recovery from embolism, and associated it with the magnitude of night-time water flux. Here, we droughted 8 highly diverse woody species (spanning tropical to semi-arid biomes) and measured xylem vulnerability curves and recovery from embolism following re-watering. We calculated xylem recovery index (XRI; percent loss of conductivity (PLC) during drought relative to PLC twelve hours following re-watering), which quantified recovery following drought. We examined traits that influence recovery from drought, including stomatal conductance (gs), transpiration, turgor loss point, photosynthesis, instantaneous water use efficiency (C13 estimated using carbon isotopes), nonstructural carbohydrates,  parenchyma starch content, specific leaf area, and wood density. We compared the impact of ambient (400 ppm) and elevated CO2 (600 ppm) on these traits.

Results/Conclusions

Plant traits associated with the highest rate of recovery from embolism and lowest rates of mortality are described for eight species. Curiously, all species exhibited rapid epicormic re-sprouting (within 12 hrs of re-watering) after extreme drought. All species exhibited some degree of xylem refilling, but Xylem Recovery Index varied extensively across species, from 10% to 90%. Several species had high night-time gs, from 50-80 mmol m-2 s-1.  Elevated CO2 altered C13 Water Use Efficiency, but did not consistently delay time to mortality in all species. Evidence of hydraulic failure (% loss of conductivity, leaf water potential, stomatal conductance) or carbohydrate depletion (photosynthesis, non-structural carbohydrates) and time to mortality are reported. Hydraulic strategies used by each species to avoid mortality are described. Further, insights into measuring vulnerability curves on long-vessel species are discussed. These results will enable prediction of which species are resilient to drought-induced mortality, and prioritise which hydraulic and carbon traits are most important to include in vegetation models.


See more of: Drought and Tree Mortality: Linking Experimental Results and Observations With Predictive Models.
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