The ACCENT-VOCBAS field campaign on biosphere-atmosphere interactions in a Mediterranean ecosystem of Castelporziano (Rome): site characteristics, climatic and meteorological conditions, and eco-physiology of vegetation

Abstract

Abstract. Biosphere-atmosphere interactions were investigated on a sandy dune Mediterranean ecosystem in a field campaign held in 2007 within the frame of the European Projects ACCENT and VOCBAS. The campaign was carried out in the Presidential estate of Castelporziano, a periurban park close to Rome. Former campaigns (e.g. BEMA) performed in Castelporziano investigated the emission of biogenic volatile organic compounds (BVOC). These campaigns focused on pseudosteppe and evergreen oak groves whereas the contribution of the largely biodiverse dune vegetation, a prominent component of the Mediterranean ecosystem, was overlooked. While specific aspects of the campaign will be discussed in companion papers, the general climatic and physiological aspects are presented here, together with information regarding BVOC emission from the most common plant species of the dune ecosystem. During the campaign regular air movements were observed, dominated by moderate nocturnal land breeze and diurnal sea breeze. A regular daily increase of ozone concentration in the air was also observed, but daily peaks of ozone were lower than those measured in summer on the same site. The site was ideal Correspondence to: F. Loreto (francesco.loreto@ibaf.cnr.it) as a natural photochemical reactor to observe reaction, transport and deposition processes occurring in the Mediterranean basin, since the sea-land breeze circulation allowed a strong mixing between biogenic and anthropogenic emissions and secondary pollutants. Measurements were run in May, when plant physiological conditions were optimal, in absence of severe drought and heat stress. Foliar rates of photosynthesis and transpiration were as high as generally recorded in unstressed Mediterranean sclerophyllous plants. Most of the plant species emitted high level of monoterpenes, despite measurements being made in a period in which emissions of volatile isoprenoids could be restrained by developmental and environmental factors, such as leaf age and relatively low air temperature. Emission of isoprene was generally low. Accounting for the high monoterpene spring emission of the dune ecosystem may be important to correct algorithms at regional and ecosystem levels, and to interpret measurements of fluxes of volatile isoprenoids and secondary pollutants.

Observations of Diurnal to Weekly Variations of Monoterpene-Dominated Fluxes of Volatile Organic Compounds from Mediterranean Forests: Implications for Regional Modeling

“…29 Most trees and shrubs of the mixed Mediterranean forest were shown to be minor isoprene emitters from gas exchange studies at the leaf level. 2,3 Our measurements confirmed that monoterpenes dominated biogenic emissions (total BEF of 1747 μg m −2 h −1 ), while isoprene emission were 1 order of magnitude lower (Figure 1). PTR-TOF-MS operating in H 3 O + mode detects isoprene at the same m/z as the fragment of methyl-butenol (m/z 69.070), 39 a compound emitted from pines in western North America, 40 whereas methyl-butenol was not found in Mediterranean stone pines.…”

“…Site details and BEF calculation methods concerning previous campaigns have been described previously. 2,4,13 Our recent field campaign was carried out in the mixed oak and pine forest between September and October 2011. The experimental site (41.744N, 12.411E) named "Castello" is primarily dominated by Pinus pinea (stone pine), Quercus ilex (holm oak), and Quercus suber (cork oak).…”

“…γ was calculated according to eq 2: (2) where γ PT describes the variation due to light and temperature; γ age makes adjustments for effects of the leaf age (1 in our case with mature foliage); γ SM accounts for direct changes due to changes in soil moisture; LAI is the leaf area index (4.77 calculated for this study); CE (=0.57) for the MEGAN canopy environment model is a factor that sets the emission activity to unity at standard conditions. To accurately estimate irradiance and leaf temperatures, we used a multilayer canopy energy balance model, 29 based on Goudriaan and van Laar 30 and Leuning.…”

“…The activity factors (γ) were calculated assuming σ and γ age = 1, and calculating γ PT using solar radiation (W m −2 ) Covariance with PTR-MS during the VOCBAS-ACCENT campaign. Also in this case, the total monoterpene fluxes were speciated using detailed analysis on BVOC emissions of the tower footprint reported in Fares et al 2 The Guenther model proposed in 1995 11 was used for the BEF calculation, which could lead to small changes in BEFs without using a canopy model. However, the PFT10 only represented 3.5% of the plant cover in the 2-degree grid unit under investigation.…”

“…10 Ten years later, a second experimental campaign took place in spring and summer 2007 on a dune-shrubland experimental site. 2,13 In this campaign, the use of a proton transfer reaction mass spectrometer (PTR-MS 14 ) provided the fast BVOC observations necessary for quasi-real-time flux measurements using Disjunct Eddy Covariance. 15 This allowed for the first time continuous measurements and BEFs calculation at canopy level.…”