title: Effect of environmental variables and stand structure on ecosystem respiration components in a Mediterranean beech forest.
abstract: The temporal variability of ecosystem respiration (RECO) has been reported to have important effects on the temporal variability of net ecosystem exchange, the net amount of carbon exchanged between an ecosystem and the atmosphere. However, our understanding of ecosystem respiration is rather limited compared with photosynthesis or gross primary productivity, particularly in Mediterranean montane ecosystems. In order to investigate how environmental variables and forest structure (tree classes) affect different respiration components and RECO in a Mediterranean beech forest, we measured soil, stem and leaf CO2 efflux rates with dynamic chambers and RECO by the eddy-covariance technique over 1 year (2007-2008). Ecosystem respiration showed marked seasonal variation, with the highest rates in spring and autumn and the lowest in summer. We found that the soil respiration (SR) was mainly controlled by soil water content below a threshold value of 0.2 m(3) m(-3), above which the soil temperature explained temporal variation in SR. Stem CO2 effluxes were influenced by air temperature and difference between tree classes with higher rates measured in dominant trees than in co-dominant ones. Leaf respiration (LR) varied significantly between the two canopy layers considered. Non-structural carbohydrates were a very good predictor of LR variability. We used these measurements to scale up respiration components to ecosystem respiration for the whole canopy and obtained cumulative amounts of carbon losses over the year. Based on the up-scaled chamber measurements, the relative contributions of soil, stem and leaves to the total annual CO2 efflux were: 56, 8 and 36%, respectively. These results confirm that SR is the main contributor of ecosystem respiration and provided an insight on the driving factors of respiration in Mediterranean montane beech forests.
authors.affiliation: Department for Innovation in Biological, Agro-Food and Forest Systems (DIBAF), University of Tuscia, Via S. Camillo de Lellis snc, 01100 Viterbo, Italy.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Guidolotti
authors.forename: Ana
authors.initials: A
authors.lastname: Rey
authors.forename: Ettore
authors.initials: E
authors.lastname: D'Andrea
authors.forename: Giorgio
authors.initials: G
authors.lastname: Matteucci
authors.forename: Paolo
authors.initials: P
authors.lastname: De Angelis
mesh_terms: D000332:Aerobiosis; D002245:Carbon Dioxide / Q000032:analysis; D017753:Ecosystem; D029964:Fagus / Q000502:physiology*; D007558:Italy; D019083:Mediterranean Region; D018515:Plant Leaves / Q000502:physiology; D018547:Plant Stems / Q000378:metabolism; D012987:Soil / Q000737:chemistry; D013696:Temperature; D013997:Time Factors; D014197:Trees / Q000502:physiology*
chemical_list: D012987:Soil; D002245:Carbon Dioxide
keywords: Fagus sylvatica; ecosystem respiration; leaf respiration; soil CO2 efflux; stem CO2 efflux; total non-structural carbohydrates