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JXB Advance Access published online on November 8, 2004
Journal of Experimental Botany, doi:10.1093/jxb/eri013
© 2004 by Oxford University Press
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Received April 27, 2004
Accepted August 17, 2004

RESEARCH PAPER

Annual and seasonal variation of sap flow and conductance of pine trees grown in elevated carbon dioxide and temperature

Kai-Yun Wang 1*, Seppo Kellomäki 2, Tianshan Zha 2, and Heli Peltola 2

1 Chengdu Institute of Biology, the Chinese Academy of Sciences, PO Box 406, Chengdu 610041, PR China; The Centre of Excellence for Forest Ecosystem and Management, University of Joensuu, PO Box 111, FIN-80101 Joensuu, Finland
2 The Centre of Excellence for Forest Ecosystem and Management, University of Joensuu, PO Box 111, FIN-80101 Joensuu, Finland

* To whom correspondence should be addressed.
Kai-Yun Wang, E-mail: kaiyun{at}joensuu.fi


  Abstract

Measurements of sap flow, crown structure, and microclimate were used to estimate the transpiration of individual 30-year-old Pinus sylvestris L. trees grown in elevated temperature and CO2. The trees were enclosed in closed-top chambers and exposed either to current ambient conditions (CON), or elevated CO2 (+350 µmol mol-1; EC), or elevated temperature (+2 to +6 °C; ET) or a combination of EC and ET (ECT) since 1996, and the measurements were made from 1999 to 2001. EC significantly increased annual sap flow per tree (F t.m) by 14% in 1999, but reduced it by 13% in 2000 and 16% in 2001. The CO2-induced increase in Ft.m in 1999 was due to a large increase in foliage area of trees, which more than compensated for a small decrease in crown conductance (Gc). The CO2-induced decreases in Ft.m in 2000 and 2001 resulted from a pronounced decline in Gc, which was much greater than the increase in foliage area. The CO2-induced increase in sensitivity of Gc at high vapour pressure deficit (VPD) did not alter the general response of sap flow to CO2 enrichment, but it did affect the diurnal courses of sap flow on some days during the main growing season (days 150-240). ET increased Ft.m by 53%, 45%, and 57% in 1999, 2000, and 2001, respectively, attributable to the combined effects of greater foliage area and maximum crown conductance, lower stomatal sensitivity to high VPD, and higher transpiration demand relative to the control treatments. There was no significant interaction between CO2 and temperature on sap flow, because ECT entailed approximately similar patterns of sap flow to ET, suggesting that the temperature played a dominate role in the case of ECT under boreal climate conditions.

Keywords: Closed-top chamber; CO2 and temperature elevation; crown conductance; Pinus sylvestris; sap flow.
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