Europ. J. Agronomy 63 (2015) 97–104 Contents lists available at ScienceDirect European Journal of Agronomy journal homepage: www.elsevier.com/locate/eja Net ecosystem carbon balance of an apple orchard Damiano Zanotelli a , Leonardo Montagnani a,b , Giovanni Manca c , Francesca Scandellari a , Massimo Tagliavini a,∗ a Faculty of Science and Technology, Free University of Bolzano-Bozen, Piazza Università 5, 39100 Bolzano, Italy b Forest Service, Autonomous Province of Bolzano-Bozen, Via Brennero 6, 39100 Bolzano, Italy c Air and Climate Unit, Institute for Environmental and Sustainability, Joint Research Centre of European Commission, Ispra, Italy article info Article history: Received 8 May 2014 Received in revised form 28 November 2014 Accepted 1 December 2014 Available online 11 December 2014 abstract Fruit tree ecosystems represent an important land use type in Southern Europe. Nevertheless, limited information and large uncertainty currently exist about their potential role as a sink of atmospheric CO 2 , which is measured through an index that accounts for all inputs and outputs of C, namely the net ecosys- tem carbon balance (NECB). In this paper, we studied the fluxes of C assimilation, the C release and the lateral C and their contribution to the NECB in an apple orchard at different time scales. Data of net ecosys- tem productivity (NEP) were recorded by eddy covariance and converted into ecosystem respiration and gross primary productivity (GPP). The net primary productivity (NPP) and the C partitioning among tree organs were also biometrically assessed. The study was carried out in the period 2009–2012 in a com- mercial apple orchard located in an intensive fruit production district of South Tyrol, Italy. We found a positive NEP from March to October and yearly NEP values of 403 g C m -2 . GPP (1346 g C m -2 year -1 on average) was highest between May and September, when leaves intercepted the highest amount of PPFD. Tree growth accounted for more than 90% of the total new biomass produced in the orchard, the remain- ing part being represented by the herbaceous vegetation covering the orchard floor. Trees allocated to fruits approximately half of the yearly NPP, while they increased only to a limited extent their standing biomass. A significant fraction of NPP was also allocated to organs (leaves, pruned woody organs, etc.,) that feed the detritus cycle. The NECB was on average positive (69 g C m -2 ) but showed high variation among years, and in the year when fruit yields was very high (74 t fruits/ha), the NECB was even negative. NECB was accounted to a greater extent by the yearly increase of tree woody organs and to a minor extent by the C transfer to the soil from the decomposing litter. The most relevant agronomical suggestion of this study is that tree vegetative growth resulting into either increasing standing biomass and/or increasing tree litter should not be reduced if we aim at maintaining the CO 2 sink capacity of the apple orchard. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The rising interest for carbon (C) budget at the global scale depends on the well documented effect of the increasing atmo- spheric carbon dioxide concentration on global temperature (IPCC, 2013). By sequestering significant amounts of C from the atmo- sphere, forests, and to a lesser extent, grasslands offer a strategy to mitigate global warming (Valentini et al., 2000; Smith et al., 2005; Luyssaert et al., 2007; Pan et al., 2011; Abdalla et al., 2013). In contrast, agricultural systems are often regarded as poten- tial sources for atmospheric carbon dioxide (Smith et al., 2008; Ciais et al., 2010; Ceschia et al., 2010; Abdalla et al., 2013). How- ∗ Corresponding author. Tel.: +39 0471 017121; fax: +39 0471 017009. E-mail address: massimo.tagliavini@unibz.it (M. Tagliavini). ever, perennial fruit plantations have intrinsic features that could contribute to maintain a long-term storage of carbon in the soil and a short- to medium-term storage in the wood. The eddy covariance approach has received large attention in the study of the C exchange between soil-vegetation and the atmosphere in forests, grasslands and other natural ecosystems (Baldocchi, 2008 http://www.fluxnet.ornl.gov/), but only limited information on woody agro-ecosystems is available (Testi et al., 2008; Zang et al., 2013; Zanotelli et al., 2013). Apple (Malus domestica) is the most extensively cultivated deciduous fruit tree crop worldwide, with a surface of 4.8 mil- lion hectares, and a production of about 76 million tons (FAOSTAT, 2012). South Tyrol is one of the most intensive apple production areas with approximately 18.000 ha and average yields of nearly 1 million tons apples year -1 . Intensively managed apple orchards have a potential for C sequestration due to: (i) an early bud burst http://dx.doi.org/10.1016/j.eja.2014.12.002 1161-0301/© 2014 Elsevier B.V. All rights reserved.