A multi-species synthesis of physiological mechanisms in drought-induced tree mortality

Adams, H.D., Zeppel, M.J.B., Anderegg, W.R.L., Hartmann, H., Landhäusser, S.M., Tissue, D.T., Huxman, T.E., Hudson, P.J., Franz, T.E., Allen, C.D., Anderegg, L.D.L., Barron-Gafford, G.A., Beerling, D.J., Breshears, D.D., Brodribb, T.J., Bugmann, H., Cobb, R.C., Collins, A.D., Dickman, L.T., Duan, H., Ewers, B.E., Galiano, L., Galvez, D.A., Garcia-Forner, N., Gaylord, M.L., Germino, M.J., Gessler, A., Hacke, U.G., Hakamada, R., Hector, A., Jenkins, M.W., Kane, J.M., Kolb, T.E., Law, D.J., Lewis, J.D., Limousin, J.-M., Love, D.M., Macalady, A.K., Martínez-Vilalta, J., Mencuccini, M., Mitchell, P.J., Muss, J.D., O'Brien, M.J., O'Grady, A.P., Pangle, R.E., Pinkard, E.A., Piper, F.I., Plaut, J.A., Pockman, W.T., Quirk, J., Reinhardt, K., Ripullone, F., Ryan, M.G., Sala, A., Sevanto, S., Sperry, J.S., Vargas, R., Vennetier, M., Way, D.A., Xu, C., Yepez, E.A., McDowell, N.G. (2017) A multi-species synthesis of physiological mechanisms in drought-induced tree mortality. Nature Ecology and Evolution. 1: 1285-1291.
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Doi: 10.1038/s41559-017-0248-x

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Manipulative experiments demonstrate how long-term soil moisture changes alter controls of plant water use

Grossiord, C., Sevanto, S., Limousin, J.-M., Meir, P., Mencuccini, M., Pangle, R.E., Pockman, W.T., Salmon, Y., Zweifel, R., McDowell, N.G. (2017) Manipulative experiments demonstrate how long-term soil moisture changes alter controls of plant water use. Environmental and Experimental Botany. : 0-0.
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Doi: 10.1016/j.envexpbot.2017.12.010

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An empirical method that separates irreversible stem radial growth from bark water content changes in trees: theory and case studies

Mencuccini, M., Salmon, Y., Mitchell, P., Hölttä, T., Choat, B., Meir, P., O'Grady, A., Tissue, D., Zweifel, R., Sevanto, S., Pfautsch, S. (2017) An empirical method that separates irreversible stem radial growth from bark water content changes in trees: theory and case studies. Plant Cell and Environment. 40: 290-303.
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Doi: 10.1111/pce.12863

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Assimilation of repeated woody biomass observations constrains decadal ecosystem carbon cycle uncertainty in aggrading forests

Smallman, T.L., Exbrayat, J.-F., Mencuccini, M., Bloom, A.A., Williams, M. (2017) Assimilation of repeated woody biomass observations constrains decadal ecosystem carbon cycle uncertainty in aggrading forests. Journal of Geophysical Research: Biogeosciences. 122: 528-545.
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Doi: 10.1002/2016JG003520

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Predicting stomatal responses to the environment from the optimization of photosynthetic gain and hydraulic cost

Sperry J.S., Venturas M.D., Anderegg W.R.L., Mencuccini M., Mackay D.S., Wang Y., Love D.M. (2017) Predicting stomatal responses to the environment from the optimization of photosynthetic gain and hydraulic cost. Plant Cell and Environment. 40: 816-830.
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Doi: 10.1111/pce.12852

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Stomatal regulation presumably evolved to optimize CO2 for H2O exchange in response to changing conditions. If the optimization criterion can be readily measured or calculated, then stomatal responses can be efficiently modelled without recourse to empirical models or underlying mechanism. Previous efforts have been challenged by the lack of a transparent index for the cost of losing water. Yet it is accepted that stomata control water loss to avoid excessive loss of hydraulic conductance from cavitation and soil drying. Proximity to hydraulic failure and desiccation can represent the cost of water loss. If at any given instant, the stomatal aperture adjusts to maximize the instantaneous difference between photosynthetic gain and hydraulic cost, then a model can predict the trajectory of stomatal responses to changes in environment across time. Results of this optimization model are consistent with the widely used Ball–Berry–Leuning empirical model (r2 > 0.99) across a wide range of vapour pressure deficits and ambient CO2 concentrations for wet soil. The advantage of the optimization approach is the absence of empirical coefficients, applicability to dry as well as wet soil and prediction of plant hydraulic status along with gas exchange. © 2016 John Wiley & Sons Ltd

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Stand dynamics modulate water cycling and mortality risk in droughted tropical forest

da Costa A.C.L., Rowland L., Oliveira R.S., Oliveira A.A.R., Binks O.J., Salmon Y., Vasconcelos S.S., Junior J.A.S., Ferreira L.V., Poyatos R., Mencuccini M., Meir P. (2017) Stand dynamics modulate water cycling and mortality risk in droughted tropical forest. Global Change Biology. : 0-0.
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Doi: 10.1111/gcb.13851

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Transpiration from the Amazon rainforest generates an essential water source at a global and local scale. However, changes in rainforest function with climate change can disrupt this process, causing significant reductions in precipitation across Amazonia, and potentially at a global scale. We report the only study of forest transpiration following a long-term (>10 year) experimental drought treatment in Amazonian forest. After 15 years of receiving half the normal rainfall, drought-related tree mortality caused total forest transpiration to decrease by 30%. However, the surviving droughted trees maintained or increased transpiration because of reduced competition for water and increased light availability, which is consistent with increased growth rates. Consequently, the amount of water supplied as rainfall reaching the soil and directly recycled as transpiration increased to 100%. This value was 25% greater than for adjacent nondroughted forest. If these drought conditions were accompanied by a modest increase in temperature (e.g., 1.5°C), water demand would exceed supply, making the forest more prone to increased tree mortality. © 2017 John Wiley & Sons Ltd.

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