Tropospheric ozone concentrations in the Catalan Pyrenees and their effects on Mountain pine (Pinus uncinata Ram.)

Abstract

This thesis aimed to study the O3 concentrations in the Pyrenees and their effects on Montain pine (Pinus uncinata Ram.), the dominant tree species of the subalpine forests of this mountainous range. We first studied the O3 concentrations trends during the last 16 years in the Catalan Pyrenees as well as the pattern of distribution of O3 and its possible origin in an altitudinal gradient in central Catalan Pyrenees. We found that the O3 concentrations in the overall Catalan Pyrenees have greatly exceeded the thresholds for protection of the vegetation set by the UNECE’s CLRTAP and the European Directive 2008/50/EC from 1994 to 2009 and show a general increasing trend over time with a slight decrease during the last 3 years. In the altitudinal transects of the Central Catalan Pyrenees we found that O3 concentrations significantly increased with altitude, with annual means at the highest site (2300 m a.s.l.) ranging from 38 to 67 ppb, showing values 35-38% greater in the warm period than in the cold period and with a characteristic pattern of minimum values early in the morning, a rise during the morning and a decline overnight. O3 mainly originated from urban areas and was transported to high mountain sites. These results suggest thus that plant life in this mountainous range is at risk of damage by O3, specifically at high-altitude sites, where exceedances of these thresholds are greater. After characterizing the O3 distribution in the Pyrenees, we surveyed the O3-like visible injury, crown defoliation and tree mortality in the previous altitudinal gradients. Under conditions of relatively high summer water availability (summer precipitation/potential evapotranspiration above 0.96), increases in the severity of the O3 visible injury were related with increases in [O3]. Crown defoliation and tree mortality mean values of 20.4-66.4% and 0.6-29.6%, respectively, pointed to poorer tree vitality than reported in previous works and were positively correlated with the accumulated O3 exposure and with variables referring to soil water availability, which again pointed to be result of a possible greater O3 uptake. Although O3 is believed to be part of the cause of the observed crown defoliation and tree mortality, further research is needed to determine the contribution of the multiple other acting stress factors. The O3-induced injury observed in Pinus uncinata stands from our study had the form of tiny and diffuse green-yellowish mottles located around the stomata lines on the light exposed side of the needles and at the microscopic level, we observed chloroplasts reduction in size and an increased oxidation of cell content from the inner to the outer mesophyll cell layers, cell wall thickenings and wart-like protrusions, accumulation of antioxidants, and accelerated cell senescence processes. The observation of the same typology of mottles in a free-air O3 fumigation experiment with Pinus uncinata saplings and the fact that most of the cytochemical markers observed below mottles in our symptomatic samples had already been observed to be induced by O3 under controlled conditions in other tree species, confirm that the observed mottles in field mature individuals of Pinus uncinata are most probably caused by the effect of O3. Finally, we conducted a two-year experiment with O3 fumigation, where it was confirmed that exposures to O3 concentrations as those of the Pyrenees, led to high occurrence and intensity of visible injury and a 24-29% reduction of root biomass on saplings of Pinus uncinata, which may render trees more susceptible to other stresses and imply long-term effects on the nutrient, carbon, and water cycles of the ecosystem.

Date of Award	18 Jul 2012
Original language	English
Supervisor	Josep Peñuelas Reixach (Director) & Angela Ribas Artola (Director)