Choat B., Jansen S., Brodribb T.J., Cochard H., Delzon S., Bhaskar R., Bucci S.J., Feild T.S., Gleason S.M., Hacke U.G., Jacobsen A.L., Lens F., Maherali H., Martínez-Vilalta J., Mayr S., Mencuccini M., Mitchell P.J., Nardini A., Pittermann J., Pratt R.B., Sperry J.S., Westoby M., Wright I.J., Zanne A.E. (2012) Global convergence in the vulnerability of forests to drought. Nature. 491: 752-755.EnllaçDoi: 10.1038/nature11688
Shifts in rainfall patterns and increasing temperatures associated with climate change are likely to cause widespread forest decline in regions where droughts are predicted to increase in duration and severity. One primary cause of productivity loss and plant mortality during drought is hydraulic failure. Drought stress creates trapped gas emboli in the water transport system, which reduces the ability of plants to supply water to leaves for photosynthetic gas exchange and can ultimately result in desiccation and mortality. At present we lack a clear picture of how thresholds to hydraulic failure vary across a broad range of species and environments, despite many individual experiments. Here we draw together published and unpublished data on the vulnerability of the transport system to drought-induced embolism for a large number of woody species, with a view to examining the likely consequences of climate change for forest biomes. We show that 70% of 226 forest species from 81 sites worldwide operate with narrow (
Martinez-Vilalta J, Mencuccini M, Alvarez X, Camacho J, Loepfe J, Pinol J (2012) Spatial distribution and packing of xylem conduits. 7th Plant Biomechanics International Conference, Clermont-Ferrand, France, 20-24 August 2012. (Comunicació oral).
Martínez-Vilalta J., Mencuccini M., Álvarez X., Camacho J., Loepfe L., Piñol J. (2012) Spatial distribution and packing of xylem conduits. American Journal of Botany. 99: 1189-1196.EnllaçDoi: 10.3732/ajb.1100384
Premise of the study: The hydraulic properties of the xylem determine the ability of plants to transport water from the soil to the leaves and to cope with important stress factors such as frost and drought. Hydraulic properties have usually been studied as a function of the anatomy of xylem conduits and their pits, but recent studies have proposed that system-level properties, related to the topology of the xylem network, may also play a role. Here we study how the spatial arrangement of conduits in xylem cross sections affects the relationship between mean conduit lumen area and conduit density (packing function) across species.Methods: Point pattern analysis was used to describe the spatial distribution of xylem conduits in 97 woody species. The effect of conduit aggregation on the packing function was tested using phylogenetic generalized least squares. A hydraulic model with an explicit description of the topology of the xylem network was used to interpret the functional significance of our findings.Key results: The spatial arrangement of conduits affected the packing function across species, so that species with aggregated distributions tended to have lower conduit densities for a given conduit size and lower conduit lumen fractions. According to our modeling results, the higher conduit-to-conduit connectivity of species with aggregated distributions allows them to achieve higher hydraulic conductivity. Species with aggregated conduits, however, pay a cost in terms of increased vulnerability to embolism.Conclusions: The spatial arrangement of conduits affects the fundamental structural and functional attributes of the xylem. © 2012 Botanical Society of America.
Mencuccini M, Martínez-Vilalta J, Hölttä T (2012) Structural limitations of water and sugar transport in trees during drought: Model characterization of the relative importance of xylem embolism, carbon starvation, and lack of phloem transport. ESA Annual Meeting 2012, Portland, OR, United States of America, 5-10 August 2012. (Comunicació oral convidada).
Poyatos R, Gornall J, Mencuccini M, Huntley B, Baxter R (2012) Seasonal controls on net branch CO2 assimilation in sub-Arctic Mountain Birch (Betula pubescens ssp. czerepanovii (Orlova) Hamet-Ahti). Agricultural and Forest Meteorology 158: 90-100.
Sterck F.J., Martínez-Vilalta J., Mencuccini M., Cochard H., Gerrits P., Zweifel R., Herrero A., Korhonen J.F., Llorens P., Nikinmaa E., Nolè A., Poyatos R., Ripullone F., Sass-Klaassen U. (2012) Understanding trait interactions and their impacts on growth in Scots pine branches across Europe. Functional Ecology. 26: 541-549.EnllaçDoi: 10.1111/j.1365-2435.2012.01963.x
Plants exhibit a wide variety in traits at different organizational levels. Intraspecific and interspecific studies have potential to demonstrate functional relationships and trade-offs amongst traits, with potential consequences for growth. However, the distinction between the correlative and functional nature of trait covariation presents a challenge because traits interact in complex ways. We present an intraspecific study on Scots pine branches and use functional multi-trait concepts to organize and understand trait interactions and their impacts on growth. Branch-level traits were assessed for 97 branches from 12 Scots pine sites across Europe. To test alternative hypotheses on cause-effect relationships between anatomical traits, hydraulic traits and branch growth, we measured for each branch: the tracheid hydraulic diameter, double cell wall thickness, cell lumen span area, wood density, cavitation vulnerability, wood-specific hydraulic conductivity, the leaf area to sapwood area ratio and branch growth. We used mixed linear effect models and path models to show how anatomical traits determine hydraulic traits and, in turn, how those traits influence growth. Tracheid hydraulic diameter was the best predictor of cavitation vulnerability (R 2=0·09 explained by path model) and specific conductivity (R 2=0·19) amongst anatomical traits. Leaf area to sapwood area ratio had the strongest direct effect on branch growth (R 2=0·19) and was positively associated with the tracheid hydraulic diameter (R 2=0·22). A number of bivariate correlations between traits could be explained by these functional relationships amongst traits. The plasticity in tracheid hydraulic diameter (10.0-15.1μm) and leaf area to sapwood area ratio (600-6051cm 2cm -2) and the maintenance of a minimum leaf water potential (between -2 and -2·5MPa) appear to drive the anatomical and hydraulic traits of Scots pine across Europe. These properties are major drivers of the functional trait network underlying the growth variation amongst pine branches and thus possibly contribute to the ecological success of pines at a local and continental scale. © 2012 The Authors. Functional Ecology © 2012 British Ecological Society.
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