title: A new positive relationship between pCO2 and stomatal frequency in Quercus guyavifolia (Fagaceae): a potential proxy for palaeo-CO2 levels.
abstract: OBJECTIVE
  The inverse relationship between atmospheric CO2 partial pressure (pCO2) and stomatal frequency in many species of plants has been widely used to estimate palaeoatmospheric CO2 (palaeo-CO2) levels; however, the results obtained have been quite variable. This study attempts to find a potential new proxy for palaeo-CO2 levels by analysing stomatal frequency in Quercus guyavifolia (Q. guajavifolia, Fagaceae), an extant dominant species of sclerophyllous forests in the Himalayas with abundant fossil relatives.
  
  
  METHODS
  Stomatal frequency was analysed for extant samples of Q. guyavifolia collected from17 field sites at altitudes ranging between 2493 and 4497 m. Herbarium specimens collected between 1926 and 2011 were also examined. Correlations of pCO2-stomatal frequency were determined using samples from both sources, and these were then applied to Q. preguyavaefolia fossils in order to estimate palaeo-CO2 concentrations for two late-Pliocene floras in south-western China.
  
  
  RESULTS
  In contrast to the negative correlations detected for most other species that have been studied, a positive correlation between pCO2 and stomatal frequency was determined in Q. guyavifolia sampled from both extant field collections and historical herbarium specimens. Palaeo-CO2 concentrations were estimated to be approx. 180-240 ppm in the late Pliocene, which is consistent with most other previous estimates.
  
  
  CONCLUSIONS
  A new positive relationship between pCO2 and stomatal frequency in Q. guyavifolia is presented, which can be applied to the fossils closely related to this species that are widely distributed in the late-Cenozoic strata in order to estimate palaeo-CO2 concentrations. The results show that it is valid to use a positive relationship to estimate palaeo-CO2 concentrations, and the study adds to the variety of stomatal density/index relationships that available for estimating pCO2. The physiological mechanisms underlying this positive response are unclear, however, and require further research.
authors: Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China, Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla 666303, China, Institute of Systematic Botany, University of Zürich, Zürich 8008, Switzerland, Department of Botany, and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4 and University of Chinese Academy of Sciences, Beijing 100049, China Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China, Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla 666303, China, Institute of Systematic Botany, University of Zürich, Zürich 8008, Switzerland, Department of Botany, and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4 and University of Chinese Academy of Sciences, Beijing 100049, China.
authors: Jin-Jin
authors: JJ
authors: Hu
authors: Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China, Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla 666303, China, Institute of Systematic Botany, University of Zürich, Zürich 8008, Switzerland, Department of Botany, and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4 and University of Chinese Academy of Sciences, Beijing 100049, China.
authors: Yao-Wu
authors: YW
authors: Xing
authors: Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China, Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla 666303, China, Institute of Systematic Botany, University of Zürich, Zürich 8008, Switzerland, Department of Botany, and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4 and University of Chinese Academy of Sciences, Beijing 100049, China.
authors: Roy
authors: R
authors: Turkington
authors: Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China, Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla 666303, China, Institute of Systematic Botany, University of Zürich, Zürich 8008, Switzerland, Department of Botany, and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4 and University of Chinese Academy of Sciences, Beijing 100049, China.
authors: Frédéric M B
authors: FM
authors: Jacques
authors: Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China, Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla 666303, China, Institute of Systematic Botany, University of Zürich, Zürich 8008, Switzerland, Department of Botany, and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4 and University of Chinese Academy of Sciences, Beijing 100049, China.
authors: Tao
authors: T
authors: Su
authors: Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China, Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla 666303, China, Institute of Systematic Botany, University of Zürich, Zürich 8008, Switzerland, Department of Botany, and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4 and University of Chinese Academy of Sciences, Beijing 100049, China.
authors: Yong-Jiang
authors: YJ
authors: Huang
authors: Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China, Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla 666303, China, Institute of Systematic Botany, University of Zürich, Zürich 8008, Switzerland, Department of Botany, and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4 and University of Chinese Academy of Sciences, Beijing 100049, China Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China, Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla 666303, China, Institute of Systematic Botany, University of Zürich, Zürich 8008, Switzerland, Department of Botany, and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4 and University of Chinese Academy of Sciences, Beijing 100049, China zhouzk@mail.kib.ac.cn.
authors: Zhe-Kun
authors: ZK
authors: Zhou
mesh_terms: D001272:Atmosphere; D002245:Carbon Dioxide / Q000378:metabolism*; D005580:Fossils; D018515:Plant Leaves / Q000033:anatomy & histology / Q000502:physiology; D054046:Plant Stomata / Q000033:anatomy & histology / Q000502:physiology*; D029963:Quercus / Q000033:anatomy & histology / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide
keywords: Q. guajavifolia; Quercus guyavifolia; Stomatal density; altitudinal gradient; atmospheric CO2 concentration; climate change; historical specimen; oak; palaeo-CO2 reconstruction; stomatal index