Aguade D., Poyatos R., Rosas T., Martinez-Vilalta J. (2015) Comparative drought responses of Quercus ilex L. and Pinus sylvestris L. In a montane forest undergoing a vegetation shift. Forests. 6: 2505-2529.LinkDoi: 10.3390/f6082505
Different functional and structural strategies to cope with water shortage exist both within and across plant communities. The current trend towards increasing drought in many regions could drive some species to their physiological limits of drought tolerance, potentially leading to mortality episodes and vegetation shifts. In this paper, we study the drought responses of Quercus ilex and Pinus sylvestris in a montane Mediterranean forest where the former species is replacing the latter in association with recent episodes of drought-induced mortality. Our aim was to compare the physiological responses to variations in soil water content (SWC) and vapor pressure deficit (VPD) of the two species when living together in a mixed stand or separately in pure stands, where the canopies of both species are completely exposed to high radiation and VPD. P. sylvestris showed typical isohydric behavior, with greater losses of stomatal conductance with declining SWC and greater reductions of stored non-structural carbohydrates during drought, consistent with carbon starvation being an important factor in the mortality of this species. On the other hand, Q. ilex trees showed a more anisohydric behavior, experiencing more negative water potentials and higher levels of xylem embolism under extreme drought, presumably putting them at higher risk of hydraulic failure. In addition, our results show relatively small changes in the physiological responses of Q. ilex in mixed vs. pure stands, suggesting that the current replacement of P. sylvestris by Q. ilex will continue. © 2015 by the authors.
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.
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