Seasonal emission of monoterpenes by the Mediterranean tree Quercus ilex in field conditions: Relations with photosynthetic rates, temperature and volatility

The relationships of monoterpene emission with temperature, light, photosyn thesis and stomatal conductance (g(s)) were studied in Quercus ilex L, tree s throughout the four annual seasons under field conditions. The highest mo noterpene emission was measured in spring and summer (midday average of 11 mu g [g DW](-1) h(-1)), whereas the lowest rates were found in autumn and w inter (midday averages of 0.51 and 0.23 mu g [g DW](-1) h(-1), respectively ), In spring and summer, limonene was the monoterpene emitted at highest ra te (midday averages of 5.27-6.69 mu g [g DW](-1) h(-1)), whereas alpha-pine ne was emitted the most in autumn and winter (midday averages of 0.31 mu g [g DW](-1) h(-1)). The monoterpenes limonene, alpha-pinene and beta-pinene represented about 75-95% of total detected monoterpenes, The total monoterp ene emission rates represented about 0.04% of carbon fixed in autumn, 0.17% in winter, 0.84-2.51% in spring and 1.22-5.13% in summer, Significant corr elations of total monoterpene emission with temperature were found when con sidering either summer emission or the emission over the entire gear, where as significant correlations with net photosynthetic rates were only found w hen considering summer season. Among individual terpenes, the most volatile , alpha-pinene and beta-pinene, were more correlated with temperature than with net photosynthetic rates whereas the less volatile limonene was more c orrelated with net photosynthetic Fate. Thus, under field conditions it see ms that dependency of monoterpene emission on photosynthetic rate or temper ature is partly related with volatility of the compounds. Influences of sea sonality, temperature, photosynthetic rates and volatility should be consid ered in inventories and models of emission rates in Mediterranean ecosystem s.