title: Vertical profiles reveal impact of ozone and temperature on carbon assimilation of Betula pendula and Populus tremula.
abstract: Rising temperature and tropospheric ozone (O(3)) concentrations are likely to affect carbon assimilation processes and thus the carbon sink strength of trees. In this study, we investigated the joint action of elevated ozone and temperature on silver birch (Betula pendula) and European aspen (Populus tremula) saplings in field conditions by combining free-air ozone exposure (1.2 × ambient) and infrared heaters (ambient +1.2&emsp14;°C). At leaf level measurements, elevated ozone decreased leaf net photosynthesis (P(n)), while the response to elevated temperature was dependent on leaf position within the foliage. This indicates that leaf position has to be taken into account when leaf level data are collected and applied. The ozone effect on P(n) was partly compensated for at elevated temperature, showing an interactive effect of the treatments. In addition, the ratio of photosynthesis to stomatal conductance (P(n)/g(s) ratio) was decreased by ozone, which suggests decreasing water use efficiency. At the plant level, the increasing leaf area at elevated temperature resulted in a considerable increase in photosynthesis and growth in both species.
authors.affiliation: Department of Biology, University of Eastern Finland, PO Box 111, FI-80101 Joensuu, Finland. maarit.maenpaa@uef.fi
authors.forename: Maarit
authors.initials: M
authors.lastname: Mäenpää
authors.forename: Johanna
authors.initials: J
authors.lastname: Riikonen
authors.forename: Sari
authors.initials: S
authors.lastname: Kontunen-Soppela
authors.forename: Matti
authors.initials: M
authors.lastname: Rousi
authors.forename: Elina
authors.initials: E
authors.lastname: Oksanen
mesh_terms: D029662:Betula / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D002244:Carbon / Q000378:metabolism; D057965:Carbon Sequestration; D057231:Climate Change; D006358:Hot Temperature; D009584:Nitrogen / Q000378:metabolism; D010126:Ozone / Q000494:pharmacology*; D010788:Photosynthesis / Q000187:drug effects; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D054046:Plant Stomata / Q000187:drug effects; D032107:Populus / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism
chemical_list: D010126:Ozone; D002244:Carbon; D009584:Nitrogen