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.EnllaçDoi: 10.1002/2016JG003520
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.EnllaçDoi: 10.1111/pce.12852
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
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.EnllaçDoi: 10.1111/gcb.13851
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.
(2016) SAPFLUXNET: towards a global database of sap flow measurements. . : -.EnllaçDoi: https://doi.org/10.1093/treephys/tpw110
Binks O., Meir P., Rowland L., da Costa A.C.L., Vasconcelos S.S., de Oliveira A.A.R., Ferreira L., Christoffersen B., Nardini A., Mencuccini M. (2016) Plasticity in leaf-level water relations of tropical rainforest trees in response to experimental drought. New Phytologist. : 0-0.EnllaçDoi: 10.1111/nph.13927
The tropics are predicted to become warmer and drier, and understanding the sensitivity of tree species to drought is important for characterizing the risk to forests of climate change. This study makes use of a long-term drought experiment in the Amazon rainforest to evaluate the role of leaf-level water relations, leaf anatomy and their plasticity in response to drought in six tree genera. The variables (osmotic potential at full turgor, turgor loss point, capacitance, elastic modulus, relative water content and saturated water content) were compared between seasons and between plots (control and through-fall exclusion) enabling a comparison between short- and long-term plasticity in traits. Leaf anatomical traits were correlated with water relation parameters to determine whether water relations differed among tissues. The key findings were: osmotic adjustment occurred in response to the long-term drought treatment; species resistant to drought stress showed less osmotic adjustment than drought-sensitive species; and water relation traits were correlated with tissue properties, especially the thickness of the abaxial epidermis and the spongy mesophyll. These findings demonstrate that cell-level water relation traits can acclimate to long-term water stress, and highlight the limitations of extrapolating the results of short-term studies to temporal scales associated with climate change. © 2016 New Phytologist Trust.
Binks, O., Meir, P., Rowland, L., Da Costa, A.C.L., Vasconcelos, S.S., De Oliveira, A.A.R., Ferreira, L., Mencuccini, M. (2016) Limited acclimation in leaf anatomy to experimental drought in tropical rainforest trees. Tree Physiology. 36: 1550-1561.EnllaçDoi: 10.1093/treephys/tpw078
Christoffersen, B.O., Gloor, M., Fauset, S., Fyllas, N.M., Galbraith, D.R., Baker, T.R., Kruijt, B., Rowland, L., Fisher, R.A., Binks, O.J., Sevanto, S., Xu, C., Jansen, S., Choat, B., Mencuccini, M., McDowell, N.G., Meir, P. (2016) Linking hydraulic traits to tropical forest function in a size-structured and trait-driven model (TFS v.1-Hydro). Geoscientific Model Development. 9: 4227-4255.EnllaçDoi: 10.5194/gmd-9-4227-2016
Nair R.K.F., Perks M.P., Mencuccini M. (2016) Decomposition nitrogen is better retained than simulated deposition from mineral amendments in a temperate forest. Global Change Biology. : 0-0.EnllaçDoi: 10.1111/gcb.13450
Nitrogen (N) deposition (NDEP) drives forest carbon (C) sequestration but the size of this effect is still uncertain. In the field, an estimate of these effects can be obtained by applying mineral N fertilizers over the soil or forest canopy. A 15N label in the fertilizer can be then used to trace the movement of the added N into ecosystem pools and deduce a C effect. However, N recycling via litter decomposition provides most of the nutrition for trees, even under heavy NDEP inputs. If this recycled litter nitrogen is retained in ecosystem pools differently to added mineral N, then estimates of the effects of NDEP on the relative change in C (ΔC/ΔN) based on short-term isotope-labelled mineral fertilizer additions should be questioned. We used 15N labelled litter to track decomposed N in the soil system (litter, soils, microbes, and roots) over 18 months in a Sitka spruce plantation and directly compared the fate of this 15N to an equivalent amount in simulated NDEP treatments. By the end of the experiment, three times as much 15N was retained in the O and A soil layers when N was derived from litter decomposition than from mineral N additions (60% and 20%, respectively), primarily because of increased recovery in the O layer. Roots expressed slightly more 15N tracer from litter decomposition than from simulated mineral NDEP (7.5% and 4.5%) and compared to soil recovery, expressed proportionally more 15N in the A layer than the O layer, potentially indicating uptake of organic N from decomposition. These results suggest effects of NDEP on forest ΔC/ΔN may not be apparent from mineral 15N tracer experiments alone. Given the importance of N recycling, an important but underestimated effect of NDEP is its influence on the rate of N release from litter. © 2016 John Wiley & Sons Ltd.
Nguyen H.T., Meir P., Wolfe J., Mencuccini M., Ball M.C. (2016) Plumbing the depths: Extracellular water storage in specialized leaf structures and its functional expression in a three-domain pressure-volume relationship. Plant, Cell and Environment. : 0-0.EnllaçDoi: 10.1111/pce.12788
A three-domain pressure-volume relationship (PV curve) was studied in relation to leaf anatomical structure during dehydration in the grey mangrove, Avicennia marina. In domain 1, relative water content (RWC) declined 13% with 0.85MPa decrease in leaf water potential, reflecting a decrease in extracellular water stored primarily in trichomes and petiolar cisternae. In domain 2, RWC decreased by another 12% with a further reduction in leaf water potential to -5.1MPa, the turgor loss point. Given the osmotic potential at full turgor (-4.2MPa) and the effective modulus of elasticity (~40MPa), domain 2 emphasized the role of cell wall elasticity in conserving cellular hydration during leaf water loss. Domain 3 was dominated by osmotic effects and characterized by plasmolysis in most tissues and cell types without cell wall collapse. Extracellular and cellular water storage could support an evaporation rate of 1mmolm-2s-1 for up to 54 and 50min, respectively, before turgor loss was reached. This study emphasized the importance of leaf anatomy for the interpretation of PV curves, and identified extracellular water storage sites that enable transient water use without substantive turgor loss when other factors, such as high soil salinity, constrain rates of water transport. © 2016 John Wiley & Sons Ltd.
Sancho-Knapik, D., Medrano, H., Peguero-Pina, J.J., Mencuccini, M., Fariñas, M.D., Álvarez-Arenas, T.G., Gil-Pelegrín, E. (2016) The application of leaf ultrasonic resonance to vitis vinifera L. suggests the existence of a diurnal osmotic adjustment subjected to photosynthesis. Frontiers in Plant Science. 7: 0-0.EnllaçDoi: 10.3389/fpls.2016.01601
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