Downscaling of ecophysiological information from natural communities to urban trees

Knowledge about ecophysiological attitudes at tree level is basic for a correct knowledge of the performance of each species in different environments, and for the comprehension of the mitigation and compensation aspects that urban vegetation may exert. Data on photosynthesis and stomata conductance may be obtained from measurements at single leaf level, but their upscaling to plant level is very complex, due to the needs of considering light extinction patterns within complex canopies, and all the other regulatory physiological and physical factors. This paper starts from the opposite direction: scaling down information about single trees photosynthesis from data collected at stand level. Keywords: CO 2 exchange flux, ecophysiology, urban vegetation, urban green planning. Riassunto: Conoscere le risposte ecofisiologiche a livello di pianta e fondamentale per determinare le performances di ogni specie in ambienti diversi, e per comprendere gli aspetti di mitigazione e compensazione che la vegetazione esercita in aree urbane. Dati puntuali su fotosintesi e conduttanza stomatica possono essere ottenuti facilmente tramite misure dirette a livello di singola foglia, ma lo scaling a livello superiore, e quindi la trasposizione dei valori alla intera pianta e una operazione complessa. Occorre infatti tenere in conto l'estinzione della radiazione foto sintetica all'interno di chiome complesse, oltre che tutti i fattori di regolazione legati alle forzanti atmosferiche e alla componente fisiologica. Questo lavoro effettua quindi un livello di scaling che tiene in considerazione questi parametri e derivando le informazioni eco fisiologiche relative ad una singola pianta a partire dai dati raccolti a livello di ecosistema. Parole chiave: Flussi di CO 2, ecofisiologia, vegetazione urbana, pianificazione verde urbano. INTRODUCTION photosynthesis process is a complex effect of interaction between the atmosphere and the vegetation surfaces. The sink of CO 2 at tree scale is more complex than the study of photosynthesis at leaf or ecosystem scales: the plant photosynthesis ability depends not only on genetic characteristics of a single specie, but also on total biomass and its volumetric and spatial distribution. The light energy that reaches the tree canopy and the single leaves is the source to activate the photosynthesis process, so the total daily CO 2 storage at plant scale is not the sum of single leaf stored terms, but it is function of the energy availability and the solar position of the geographical location where the plant is located (Ross, 1975). Also the local meteorological and climatological conditions play a fundamental role in the determination of seasonal and annual photosynthesis (Carrara et al., 2004): the air temperature is crucial in the variability of the plant respiration and the photosynthetic active radiation (PAR), as well as water wailability, modulate the changes in the photosynthesis fluxes. Therefore, the complete knowledge of all these regulating factors is necessary to estimate the net canopy exchanges.