Author's personal copy Ozone visible symptoms and reduced root biomass in the subalpine species Pinus uncinata after two years of free-air ozone fumigation Maria Díaz-de-Quijano a, b, * , Marcus Schaub b , Seraina Bassin c , Matthias Volk c , Josep Peñuelas a a Global Ecology Unit CREAF-CEAB-CSIC, CREAF (Center for Ecological Research and Forestry Applications), Edifici C, Universitat Autònoma de Barcelona, 08193 Bellaterra, Catalonia, Spain b Swiss Federal Research Institute WSL, Zürcherstrasse 111, CH-8903 Birmensdorf, Switzerland c Air Pollution/Climate Group, Agroscope Research Station ART, Reckenholzstrasse 191, CH-8046 Zurich, Switzerland article info Article history: Received 4 November 2011 Received in revised form 6 February 2012 Accepted 17 February 2012 Keywords: Ozone Pyrenees Pinus uncinata Visible injury Root biomass abstract Concentrations of ozone often exceed the thresholds of forest protection in the Pyrenees, but the effect of ozone on Pinus uncinata, the dominant species in subalpine forests in this mountainous range, has not yet been studied. We conducted an experiment of free-air ozone fumigation with saplings of P. uncinata fumigated with ambient O 3 (AOT40 MayeOct: 9.2 ppm h), 1.5  O 3amb (AOT40 MayeOct: 19.2 ppm h), and 1.8  O 3amb (AOT40 MayeOct: 32.5 ppm h) during two growing seasons. We measured chlorophyll content and fluorescence, visible injury, gas exchange, and above- and below-ground biomass. Increased exposures to ozone led to a higher occurrence and intensity of visible injury from O 3 and a 24e29% reduction of root biomass, which may render trees more susceptible to other stresses such as drought. P. uncinata is thus a species sensitive to O 3 , concentrations of which in the Pyrenees are already likely affecting this species. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Tropospheric ozone is considered the most perturbing air pollutant for forests (Matyssek et al., 2007). Concentrations of ground-level O 3 have been increasing during the last century, from a mean level of 10 ppb (Anfossi and Sandroni, 1994) at the end of the 19th century to a present annual average concentration of 35e40 ppb in the mid-latitudes of the Northern Hemisphere (Fowler et al., 2008). Moreover, the IPCC (Intergovernmental Panel on Climate Change) predicts an increase in concentrations of O 3 of 20e25% from 2015 to 2050 based on scenarios of high emissions (IPCC, 2007). At present, concentrations of O 3 at mid-latitudes of the Northern Hemisphere already exceed the threshold levels for the protection of vegetation, and the risk to vegetation is expected to increase as the projected concentrations increase (Fowler et al., 2008). Several studies have revealed that O 3 has negative effects on the health of both broadleaved and coniferous trees (Calatayud et al., 2011; Krupa et al., 1998). Damage from ozone has been exten- sively studied for, among other species, Fagus sylvatica, Betula pendula, Picea abies, Picea sitchensis, Pinus ponderosa, Pinus strobus and Pinus sylvestris due to their sensitivity to ozone, abundance, distribution, and economic value (Arbaugh et al., 2003; Bartholomay et al., 1997; Manninen et al., 2003; Novak et al., 2008; Peñuelas et al., 1994; Pretzsch et al., 2010; Schaub et al., 2007; VanderHeyden et al., 2001). However, we need to further study the possible effect of O 3 on other species of trees that, like Pinus unci- nata, are very important in particular regions where concentrations of O 3 highly exceed the thresholds for the protection of vegetation, as occurs in the Pyrenees. The Mountain pine (Pinus uncinata Ram.) is an autochthonous European species found in the Central and Western Alps, the Central and Eastern Pyrenees, and the Northern Appennines. In the Pyrenees, the lower altitudinal limit of P. uncinata is at 1200 m a.s.l. and it represents the dominant subalpine forest species from 1600 to 1800 (depending on the area) to 2400 m a.s.l. (Burriel et al., 2004). Possible impacts of O 3 on forests of Pinus uncinata and on the livelihoods of forest-dependent communities could result in major ecological, economic, and social consequences. In fact, significant increases in crown defoliation in stands of P. uncinata in the Pyrenees have already been detected by the Catalan forestry service and have been reported in a previous study (Carnicer et al., 2011). The study of the sensitivity to O 3 of this tree species common in subalpine forests is thus necessary. The valley bottoms in the central region of the Catalan Pyrenees have been experiencing high levels of tropospheric ozone, with AOT40 (ApreSept) ranging from * Corresponding author. E-mail address: m.diaz@creaf.uab.cat (M. Díaz-de-Quijano). Contents lists available at SciVerse ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol 0269-7491/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2012.02.011 Environmental Pollution 169 (2012) 250e257