JME 2004

JME 2004


The Pianosa_LAB: An integrated research project to assess the carbon balance of Pianosa island

R. Baraldi, F. P. Vaccari, M. R. Colom, M. F. Cotrufo, L. P. D’Acqui

Major efforts have been made over the last decade to investigate and quantify gas exchange between the terrestrial biosphere and the atmosphere. Such exchange is, in fact, of special relevance as it is known to exert a major control on the global carbon (C) cycle. The Pianosa_LAB is a research project started in the 2000 in collaboration with the National Research Council, several Universities and the authorities of the National Tuscan Archipelago Park, to understand and quantify the C cycle in a confined ecosystem such as that of the island of Pianosa, by conventional and innovative research approaches. The island of Pianosa is especially suited for this type of investigation due to its special topography. The island is completely flat emerging only approximately of 15 m out of the sea surface. In addition, there are no anthropogenic sources of greenhouse gases on the island that may interfere with the proposed measurements, that provide useful information to quantify interactions and feedbacks between climate and local terrestrial ecosystem. The island of Pianosa is an excellent good analogue for a typical Mediterranean ecosystem where the natural vegetation is currently colonising the abandoned agricultural land and undergoing a process of re-naturalization. Furthermore, the Pianosa_LAB is attempting to integrate other activities, beside C cycle research, within the local context of a protected area thus creating synergies between science, environmental protection and the society. Here we present the main characteristic in terms of climate, geology, soil, vegetation and land-use of the island as well as its history, and describe the structure and objectives of the Pianosa_LAB project.

Keywords: carbon cycle, carbon fluxes, mediterranean ecosystem.

Soil Carbon Storage and Sequestration on Pianosa Island

C.A. Santi, L.P. D’Acqui, A. Dodero, B. Pezzarossa, R. Pini, F. Petacco, M. Scatena, R. Risaliti

The soils of Pianosa, substantially homogeneous with regard to their parent material and pedological evolution, have different agronomic histories. However, the effects of agricultural activities on soil and vegetation are still very recognizable, even if there has been no human activity for seven years. Representative areas characterized by different land use were selected to give an overview of the soil of the mains ecosystems. Soil ecosystems were characterized on the basis of their chemical, physical and biological properties. The total organic and inorganic C content of the island soils was calculated and a map of distribution of soil organic carbon was drawn up. This was done in order to obtain a basis for the assessment of the dynamics of organic C as influenced by human activities, and the relationships between ecosystems and C sequestration. Physical and chemical analysis showed the impact of human activity on soil fertility. Modifications of soil structure were observed and a noteworthy reduction of soil organic C and N contents was found both in the abandoned arable areas and in the permanent pasture land compared to the macchia ecosystem, considered as the natural starting condition. However, the microbial properties showed a good biochemical recovery of the soil previously subjected to cultivation, providing interesting information both on CO2 exchanges and on resilience of the island soil ecosystems.

Keywords: Carbon fluxes, Climate changes, Soil organic matter.

Litter decomposition and soil CO2 efflux on the Mediterranean island of Pianosa

M. F. Cotrufo, G. Delle Vedove, J.A. Subke, I. Inglima, G. Alberti and A. Peressotti

Mediterranean ecosystems are particularly vulnerable to changes in climate and land use forecasted for the near future, with likely perturba-tions of the carbon cycle. The aim of our study was to quantify particular aspects of the carbon cycle in typical Mediterranean ecosystems, in particular (1) the decay rates of litter from common tree and shrub species, (2) the efflux of CO2 from the soil and its relation to soil and litter moisture, and (3) the dynamics of the stable isotope 13C during litter decomposition. Filed work was conducted on the island Pianosa, which comprises a range of common Mediterranean ecosystem types. Litter decay rates of three selected species (Cistus monspenliensis, Pistacia lentiscus and Juniperus phoenicia) were found to be low with an average of 70 % of initial mass remaining after 2 years of field incubation. Over the same period, all litter types showed only a slight (<10 %) net loss of N. Despite relatively high initial N contents, litter decay rates were comparable to those reported in the literature, suggesting that C and N dynamics are decoupled during litter decomposition. Over the two years of incubation, 13C dynamics were not unanimous between the three litter types, with only a slight enrichment in one species. Continuation of this ongoing experiment is likely to resolve the long term effects of decomposition on 13C enrichment on litter. Soil CO2 efflux was found to be unusually high (peak rates of over 9 µmol m-2 s-1), owing to both high soil water content and soil temperature during an intensive measuring campaign in October 2003. Mean daily fluxes in woodland ecosystems were significantly higher than in either macchia or ex agricultural ecosystems, exceeding the latter about twofold. However, when scaled to the relative surface representation on Pianosa, the highest contribution of daily soil CO2 efflux stems from Macchia type vegetation, followed by abandoned agricultural sites and woodland ecosystems (around 20, 22, and 8.5 t C d-1, respectively). With the exception of one site, soil CO2 efflux correlated positi-vely with litter content at different sites across the island. Rather than causing the higher fluxes directly, higher litter contents are likely to indicate higher site productivity rates, resulting in higher CO2 turnover dynamics and hence higher overall soil CO2 efflux rates. Owing to the only small range of soil moisture conditions during the measuring campaign, no dependence of soil CO2 efflux on soil moisture could be detected. However, a range of moisture conditions between sites was noted, indicating the significance of site specific conditions also within the same ecosystem types.

Keywords: Soil respiration; Litter mass loss; Stable C isotopes; Land use

Pianosa Island: Structure, Functioning and Biodiversity of Main Ecosystems

Colom M.R., F.P. Vaccari, A. Scartazza, E. Brugnoli, G. Zerbi, S. Sforzi, R. Baraldi, Cotrufo M.F.

Structure, ecophysiology and productivity of the main island ecosystems were studied. The studied ecosystems showed a different species composition, with different dominant plant species. All ecosystems showed a high plant species richness (between 21 to 30), with a higher proportion of perennials (60 %) and a lower percentage of annuals (40 %). Herbaceous plants (85-98 %) were dominant with respect to woody species. Woody plants are the 14 % of the total number of species found in macchia and woodland ecosystems. In each type of ecosystems plant communities were dominated by few species, as for example, Avena barbata in pasture/cultivated fields, or Juniperus phoenicia in macchia ecosystems. On pasture/cultivated fields a progressive invasion of pioneer shrub species is actually undergoing. Species association of macchia vegetation is very similar to so called “Ginepreto Rupestre”, while some macchia areas showed a canopy height typical of Meso-Mediterranean Macchia. The pasture/cultivated fields and the macchia areas cover around the 53 and 37 % of island surface. On the other hand, a great fraction of island dry biomass was formed by macchia vegetation (61 %), while pasture/cultivated fields vegetation represent around the 26 % and woodlands only the 13 % of island biomass. In woodlands, species richness was associated to a higher Simpson index (0.502) with respect to macchia and pasture/cultivated fields. However the Shannon diversity index was found higher in macchia sites (0.415). Woodlands were also characterized by a higher diversity between families, as indicated by the Shannon index values, that were around 2.6, with respect to macchia (1,17) and pasture/cultivated fields (1.29). Carbon isotope composition (d13C) on leaf dry matter was used to assess differences in photosynthetic carbon isotope discrimination (?) and water-use efficiency (WUE) of the dominant species colonizing the main island ecosystems. This analysis indicated lower ? and, hence, higher WUE in macchia and woodland ecosystem species than those of abandoned agricultural fields. During the warm summer Rosmarinus officinalis showed the highest photosynthetic rates (around 10 µmol m-2s-1), within macchia vegetation. Carbon density for macchia vegetation was around 0.99 Kg of C m-2 , while nitrogen was 0.013 Kg of N m-2. Data colleted suggested that a re-naturalization processes it is actually occurring on Pianosa island, particularly on pasture/cultivated fields. Plant communities within each type of ecosystem studied, showed a similar species composition. Therefore, Pianosa island represents an important spot for biodiversity conservation and carbon sequestration in the Mediterranean sea, however data collected are not exhaus-tive to know the entire functioning and structure of the island, but indicate that those species that are more abundant in the three ecosystems probably will be the driving forces of ecosystem responses to changing environmental conditions.

Keywords: carbon, carbon isotope composition, photosynthesis, species, vegetation

Emission and flux of terpenoids released from the terrestrial ecosystems present in the Pianosa Island

P. Ciccioli, R. Baraldi, M. Mannozzi, F. Rapparini, M. Nardino, F. Miglietta, E. Brancaleoni E. & M.

For the first time, the emission of individual BVOC released from a Mediterranean ecosystem has been assessed and the results obtained have been directly compared with fluxes measured with the mixed box (MB) approach. The study was conducted in Pianosa, a very small and flat island located in the Tyrrhenian sea, between the coasts of Central Italy and the Corsica Island. Due to the substantial lack of man-made emission and the restricted access, terrestrial vegetation represents in this island the main source of hydrocarbons. This allows to use simple methodologies to estimate and measure the emission of individual BVOC in the atmosphere. Due to the limited number of emitting species, the total emission was estimated by up-scaling to ecosystem level the information obtained with branch enclosures. Data obtained suggested that the basal emission of total isoprenoids generated from the island was one order of magnitude smaller than that estimated in the pine-oak forest ecosystem of Castelporziano (ca. 0.2 mg C m-2h-1). a-Pinene was the major component emitted and accounted, by itself, for more than 40% of the total isoprenoid emission. Daily profiles of emission were calculated for the two days when the air masses were depleted in anthropogenic compounds, after traveling for two days over the open sea. Results obtained in these days indicated that a-pinene was the only component displaying an emission (ca. 0.1 mg C m-2 h-1) sufficiently high to generate detectable concentrations (0.01-0.03 µg C Nm-3) in the atmospheric boundary layer (ABL). Fluxes determined using the MB approach substantially confirmed the estimates made by up-scaling to ecosystem level the emission from terrestrial vegetation, although a difference of a factor of two was observed between the calculated emission and the measured fluxes. Reasons explaining these differences will be analyzed and critically discussed.

Keywords: branch enclosure, Mediterranean ecosystem, mixed box technique, isoprenoids, tethered balloon.

Net Ecosystem Carbon Exchange (NEE) of the Island of Pianosa

F. P. Vaccari, B. Gioli, A. Zaldei, F. Sabatini, T. Georgiadis, F. Rossi, A. Peressotti, V. Magliulo

The overall gas exchange occurring between Mediterranean ecosystems and the atmosphere has been rarely quantified experimentally, but due to the occurrence of prolonged summer drought that limits gas exchange, the potential carbon (C) sink of Mediterranean ecosystems is generally considered low. Net Ecosystem C Exchange (NEE) was measured for a period of 12 months in the Island of Pianosa (Central Italy) using the eddy covariance technique. The Island is partly covered by macchia vegetation and by abandoned agricultural land and it is ideal for flux measurements due to its flat topography and for the absence of anthropogenic C sources. C-flux measurements made between April 2002 and March 2003 showed that the Island of Pianosa was a net sink of C during a 12 months period accumulating 2.64 t C ha-1 per year. Such a sink was less than what has been reported for evergreen forest in the region, but it is larger than what is generally estimated for drought limited ecosystems. The analysis of seasonal changes in the C-flux revealed that phenology and temperature were likely limiting C uptake during the winter months, while drought was limiting during the summer months. The potential C sink that could be provided by the entire island was finally calculated as the difference between the C stock contained at present in the Island’s ecosystems and that contained in the areas covered by the Mediterranean macchia.

Keywords: Eddy covariance, Mediterranean ecosystem, Net Ecosystem Exchange, Pianosa island

Computation of the mixed layer height through a simplified PBL model for small island (ISLA)

Marianna Nardino, Osvaldo Facini, Teodoro Georgiadis, Federica Rossi and Alessandro Zaldei

In the present work a simplified model, based on the parameterisation of a growing boundary layer over a coastal discontinuity , has been used to estimate the temporal evolution of the mixed layer height during the PianosaLab experimental campaigns. The bi-dimensional model was applied over the limited surface domain of the Pianosa island. The input parameters of the model derive from the sonic anemometer measurements collected at a ground site (Vaccari et al., same issue).

Keywords: Planetary boundary layer, Turbulence modelling, Mixing layer