Lloret F., Sapes G., Rosas T., Galiano L., Saura-Mas S., Sala A., Martínez-Vilalta J. (2018) Non-structural carbohydrate dynamics associated with drought-induced die-off in woody species of a shrubland community. Annals of Botany. 121: 1383-1396.LinkDoi: 10.1093/aob/mcy039
Background and Aims The relationship between plant carbon economy and drought responses of co-occurring woody species can be assessed by comparing carbohydrate (C) dynamics following drought and rain periods, relating these dynamics to species' functional traits. We studied nine woody species coexisting in a continental Mediterranean shrubland that experienced severe drought effects followed by rain. Methods We measured total non-structural carbohydrates (NSC) and soluble sugars (SS) in roots and stems during drought and after an autumn rain pulse in plants exhibiting leaf loss and in undefoliated ones. We explored whether their dynamics were related to foliage recovery and functional traits (height [H], specific leaf area [SLA], wood density [WD]). Key Results During drought, NSC concentrations were overall lower in stems and roots of plants experiencing leaf loss, while SS decreases were smaller. Roots had higher NSC concentrations than stems. After the rain, NSC concentrations continued to decrease, while SS increased. Green foliage recovered after rain, particularly in plants previously experiencing higher leaf loss, independently of NSC concentrations during drought. Species with lower WD tended to have more SS during drought and lower SS increases after rain. In low-WD species, plants with severe leaf loss had lower NSC relative to undefoliated ones. No significant relationship was found between H or SLA and C content or dynamics. Conclusions Our community-level study reveals that, while responses were species-specific, C stocks overall diminished in plants affected by prolonged drought and did not increase after a pulse of seasonal rain. Dynamics were faster for SS than NSC. We found limited depletion of SS, consistent with their role in basal metabolic, transport and signalling functions. In a scenario of increased drought under climate change, NSC stocks in woody plants are expected to decrease differentially in coexisting species, with potential implications for their adaptive abilities and community dynamics. © The Author(s) 2018.
Doblas-Miranda, E., Alonso, R., Arnan, X., Bermejo, V., Brotons, L., de las Heras, J., Estiarte, M., Hódar, J.A., Llorens, P., Lloret, F., López-Serrano, F.R., Martínez-Vilalta, J., Moya, D., Peñuelas, J., Pino, J., Rodrigo, A., Roura-Pascual, N., Valladares, F., Vilà, M., Zamora, R., Retana, J. (2017) A review of the combination among global change factors in forests, shrublands and pastures of the Mediterranean Region: Beyond drought effects. Global and Planetary Change. 148: 42-54.LinkDoi: 10.1016/j.gloplacha.2016.11.012
Greenwood, S., Ruiz-Benito, P., Martínez-Vilalta, J., Lloret, F., Kitzberger, T., Allen, C.D., Fensham, R., Laughlin, D.C., Kattge, J., Bönisch, G., Kraft, N.J.B., Jump, A.S. (2017) Tree mortality across biomes is promoted by drought intensity, lower wood density and higher specific leaf area. Ecology Letters. 20: 539-553.LinkDoi: 10.1111/ele.12748
Jump, A.S., Ruiz-Benito, P., Greenwood, S., Allen, C.D., Kitzberger, T., Fensham, R., Martínez-Vilalta, J., Lloret, F. (2017) Structural overshoot of tree growth with climate variability and the global spectrum of drought-induced forest dieback. Global Change Biology. : 0-0.LinkDoi: 10.1111/gcb.13636
Ruiz-Benito, P., Ratcliffe, S., Zavala, M.A., Martínez-Vilalta, J., Vilà-Cabrera, A., Lloret, F., Madrigal-González, J., Wirth, C., Greenwood, S., Kändler, G., Lehtonen, A., Kattge, J., Dahlgren, J., Jump, A.S. (2017) Climate- and successional-related changes in functional composition of European forests are strongly driven by tree mortality. Global Change Biology. : 0-0.LinkDoi: 10.1111/gcb.13728
Cailleret, M., Jansen, S., Robert, E.M.R., Desoto, L., Aakala, T., Antos, J.A., Beikircher, B., Bigler, C., Bugmann, H., Caccianiga, M., Čada, V., Camarero, J.J., Cherubini, P., Cochard, H., Coyea, M.R., Čufar, K., Das, A.J., Davi, H., Delzon, S., Dorman, M., Gea-Izquierdo, G., Gillner, S., Haavik, L.J., Hartmann, H., Hereş, A.-M., Hultine, K.R., Janda, P., Kane, J.M., Kharuk, V.I., Kitzberger, T., Klein, T., Kramer, K., Lens, F., Levanic, T., Linares Calderon, J.C., Lloret, F., Lobo-Do-Vale, R., Lombardi, F., López Rodríguez, R., Mäkinen, H., Mayr, S., Mészáros, I., Metsaranta, J.M., Minunno, F., Oberhuber, W., Papadopoulos, A., Peltoniemi, M., Petritan, A.M., Rohner, B., Sangüesa-Barreda, G., Sarris, D., Smith, J.M., Stan, A.B., Sterck, F., Stojanović, D.B., Suarez, M.L., Svoboda, M., Tognetti, R., Torres-Ruiz, J.M., Trotsiuk, V., Villalba, R., Vodde, F., Westwood, A.R., Wyckoff, P.H., Zafirov, N., Martínez-Vilalta, J. (2016) A synthesis of radial growth patterns preceding tree mortality. Global Change Biology. : 0-0.LinkDoi: 10.1111/gcb.13535
Martínez-Vilalta J., Lloret F. (2016) Drought-induced vegetation shifts in terrestrial ecosystems: The key role of regeneration dynamics. Global and Planetary Change. 144: 94-108.LinkDoi: 10.1016/j.gloplacha.2016.07.009
Ongoing climate change is modifying climatic conditions worldwide, with a trend towards drier conditions in most regions. Vegetation will respond to these changes, eventually adjusting to the new climate. It is unclear, however, how close different ecosystems are to climate-related tipping points and, thus, how dramatic these vegetation changes will be in the short- to mid-term, given the existence of strong stabilizing processes. Here, we review the published evidence for recent drought-induced vegetation shifts worldwide, addressing the following questions: (i) what are the necessary conditions for vegetation shifts to occur? (ii) How much evidence of drought-induced vegetation shifts do we have at present and where are they occurring? (iii) What are the main processes that favor/oppose the occurrence of shifts at different ecological scales? (iv) What are the complications in detecting and attributing drought-induced vegetation shifts? (v) What ecological factors can interact with drought to promote shifts or stability? We propose a demographic framework to classify the likely outcome of instances of drought-induced mortality, based upon the survival of adults of potential replacement species and the regeneration of both formerly dominant affected species and potential replacement species. Out of 35 selected case studies only eight were clearly consistent with the occurrence of a vegetation shift (species or biome shift), whereas three corresponded to self-replacements in which the affected, formerly dominant species was able to regenerate after suffering drought-induced mortality. The other 24 cases were classified as uncertain, either due to lack of information or, more commonly, because the initially affected and potential replacement species all showed similar levels of regeneration after the mortality event. Overall, potential vegetation transitions were consistent with more drought-resistant species replacing less resistant ones. However, almost half (44%) of the vegetation trajectories associated to the 35 case studies implied no change in the functional type of vegetation. Of those cases implying a functional type change, the most common one was a transition from tree- to shrub-dominated communities. Overall, evidence for drought-induced vegetation shifts is still limited. In this context, we stress the need for improved, long-term monitoring programs with sufficient temporal resolution. We also highlight the critical importance of regeneration in determining the outcome of drought-induced mortality events, and the crucial role of co-drivers, particularly management. Finally, we illustrate how placing vegetation shifts in a biogeographical and successional context may support progress in our understanding of the underlying processes and the ecosystem-level implications. © 2016 Elsevier B.V.
Martínez-Vilalta, J., Sala, A., Asensio, D., Galiano, L., Hoch, G., Palacio, S., Piper, F.I., Lloret, F. (2016) Dynamics of non-structural carbohydrates in terrestrial plants: A global synthesis. Ecological Monographs. 86: 495-516.LinkDoi: 10.1002/ecm.1231
Quentin A.G., Pinkard E.A., Ryan M.G., Tissue D.T., Baggett L.S., Adams H.D., Maillard P., Marchand J., Landhäusser S.M., Lacointe A., Gibon Y., Anderegg W.R.L., Asao S., Atkin O.K., Bonhomme M., Claye C., Chow P.S., Clément-Vidal A., Davies N.W., Dickman L.T., Dumbur R., Ellsworth D.S., Falk K., Galiano L., Grünzweig J.M., Hartmann H., Hoch G., Hood S., Jones J.E., Koike T., Kuhlmann I., Lloret F., Maestro M., Mansfield S.D., Martínez-Vilalta J., Maucourt M., McDowell N.G., Moing A., Muller B., Nebauer S.G., Niinemets U., Palacio S., Piper F., Raveh E., Richter A., Rolland G., Rosas T., Joanis B.S., Sala A., Smith R.A., Sterck F., Stinziano J.R., Tobias M., Unda F., Watanabe M., Way D.A., Weerasinghe L.K., Wild B., Wiley E., Woodruff D.R. (2015) Non-structural carbohydrates in woody plants compared among laboratories. Tree Physiology. 35: 1146-1165.LinkDoi: 10.1093/treephys/tpv073
Non-structural carbohydrates (NSC) in plant tissue are frequently quantified to make inferences about plant responses to environmental conditions. Laboratories publishing estimates of NSC of woody plants use many different methods to evaluate NSC. We asked whether NSC estimates in the recent literature could be quantitatively compared among studies. We also asked whether any differences among laboratories were related to the extraction and quantification methods used to determine starch and sugar concentrations. These questions were addressed by sending sub-samples collected from five woody plant tissues, which varied in NSC content and chemical composition, to 29 laboratories. Each laboratory analyzed the samples with their laboratory-specific protocols, based on recent publications, to determine concentrations of soluble sugars, starch and their sum, total NSC. Laboratory estimates differed substantially for all samples. For example, estimates for Eucalyptus globulus leaves (EGL) varied from 23 to 116 (mean = 56) mg g-1 for soluble sugars, 6-533 (mean = 94) mg g-1 for starch and 53-649 (mean = 153) mg g-1 for total NSC. Mixed model analysis of variance showed that much of the variability among laboratories was unrelated to the categories we used for extraction and quantification methods (method category R2 = 0.05-0.12 for soluble sugars, 0.10-0.33 for starch and 0.01-0.09 for total NSC). For EGL, the difference between the highest and lowest least squares means for categories in the mixed model analysis was 33 mg g-1 for total NSC, compared with the range of laboratory estimates of 596 mg g-1. Laboratories were reasonably consistent in their ranks of estimates among tissues for starch (r = 0.41-0.91), but less so for total NSC (r = 0.45-0.84) and soluble sugars (r = 0.11-0.83). Our results show that NSC estimates for woody plant tissues cannot be compared among laboratories. The relative changes in NSC between treatments measured within a laboratory may be comparable within and between laboratories, especially for starch. To obtain comparable NSC estimates, we suggest that users can either adopt the reference method given in this publication, or report estimates for a portion of samples using the reference method, and report estimates for a standard reference material. Researchers interested in NSC estimates should work to identify and adopt standard methods. © The Author 2015.
Barba J., Curiel Yuste J., Martinez-Vilalta J., Lloret F. (2013) Drought-induced tree species replacement is reflected in the spatial variability of soil respiration in a mixed Mediterranean forest. Forest Ecology and Management. 306: 79-87.LinkDoi: 10.1016/j.foreco.2013.06.025
As episodes of drought-induced forest mortality are being increasingly reported worldwide and may become more frequent in the future as a result of climate change, it is essential to characterize their functional implications in terms of ecosystem carbon and water fluxes. We investigated the spatial variability of soil respiration in a mixed Mediterranean forest located on rugged terrain, where Scots pine (Pinus sylvestris) is affected by drought-induced dieback and appears to have been replaced by Holm oak (Quercus ilex) as the dominant tree species. Soil respiration was measured in spring 2010 on two plots (16.2×16.2m) using a static closed chamber method (soda lime technique) and a systematic sampling (1.8-m grid) including 100 points per plot. Biotic and abiotic variables, such as soil moisture, soil temperature, soil organic matter content, stoniness, pH, fine root C:N ratio and biomass, tree basal area and tree species and health condition of nearest neighbouring tree were also recorded. Our results showed that the spatial variability of soil respiration under optimal environmental conditions (spring) was high and showed no spatial autocorrelation on the scale studied (1-18m). A mixed-effects model applied to explain the spatial variability of soil respiration indicated that only the variables related to forest structure (i.e., health condition and basal area) explained any of the observed variability of soil respiration (R2=0.45). Our model revealed that soil respiration was highest in soils close to dead pines and under Holm oak trees, suggesting that tree mortality and species replacement of pine trees by Holm oak may lead to higher soil respiration fluxes. The direct effect of tree mortality on soil respiration may be a transitory response caused by fine root mortality. Furthermore, the fact that tree species replacement as a result of drought-induced die-off is accompanied by concomitant changes in soil respiration has important implications for soil and ecosystem carbon balance. © 2013 Elsevier B.V.
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