Tree height strongly affects estimates of water-use efficiency responses to climate and CO2 using isotopes
2017
Brienen, R. J. W. | Gloor, E. | Clerici, S. | Newton, R. | Arppe, L. | Boom, A. | Bottrell, S. | Callaghan, M. | Heaton, T. | Helama, Samuli | Helle, G. | Leng, M. J. | Mielikäinen, K. | Oinonen, M. | Timonen, Mauri | School of Geography, University of Leeds | School of Earth and Environment, University of Leeds | Laboratory of Chronology, Finnish Museum of Natural History-Luomus, University of Helsinki | School of Geography, University of Leicester | NERC Isotope Geosciences Facilities, British Geological Survey | GFZ - german Research Centre for Geosciences, Section 5.2 Climate Dynamics and Landscape Evolution | Centre for Environmental Geochemistry, University of Nottingham | Natural Resources Institute Finland (Luke) | Luke / Luonnonvarat ja biotuotanto / Ympäristövaikutukset / Ilmastonmuutoksen hillintä ja sopeutuminen (4100100411) | Luke / Uudet liiketoimintamahdollisuudet / Uudet tuotteet ja teknologiat / Bioraaka-aineet ja tuoteominaisuudet (4100300313) | 4100100411 | 4100300313
Various studies report substantial increases in intrinsic water-use efficiency (Wi), estimated using carbon isotopes in tree rings, suggesting trees are gaining increasingly more carbon per unit water lost due to increases in atmospheric CO2. Usually, reconstructions do not, however, correct for the effect of intrinsic developmental changes in Wi as trees grow larger. Here we show, by comparingWi across varying tree sizes at one CO2 level, that ignoring such developmental effects can severely affect inferences of trees’ Wi. Wi doubled or even tripled over a trees’ lifespan in three broadleaf species due to changes in tree height and light availability alone, and there are also weak trends for Pine trees. Developmental trends in broadleaf species are as large as the trends previously assigned to CO2 and climate. Credible future tree ring isotope studies require explicit accounting for species-specific developmental effects before CO2 and climate effects are inferred.
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