Original article Enhancing prediction accuracy of soil respiration in an apple orchard by integrating photosynthetic activity into a temperature-related model F. Scandellari a, * , D. Zanotelli a , C. Ceccon a , M. Bolognesi a , L. Montagnani a , P. Cassol b , G.W. Melo c , M. Tagliavini a a Free University of Bolzano-Bozen, Faculty of Science and Technology, Piazza Universit a, 1, I-39100 Bolzano-Bozen, Italy b Universidade do estado de Santa Catarina, Centro de Ci^ encias Agroveterin arias, Av. Luiz de Cam~ oes, 2090, 88520-000 Lages, SC, Brazil c Empresa Brasileira de Pesquisa Agropecu aria, Centro Nacional de Pesquisa de Uva e Vinho, Rua Livramento, 515, 95700-000 Bento Gonçalves, RS, Brazil article info Article history: Received 18 May 2015 Received in revised form 21 July 2015 Accepted 22 July 2015 Available online xxx Keywords: Carbon Gross primary productivity Light Net primary productivity Roots abstract Temperature is often used as the primary driver to model soil respiration (R S ) and several models based only on temperature have been used to estimate it, with a variable degree of accuracy. An adequate availability of photosynthates translocated from the canopy also affects root respiration (R R ) and therefore R S . In this work, carried out in an apple orchard for three years, we assessed the role of temperature to R S and its autotrophic (R R ) and heterotrophic (R H ) components. We also determined the variation over the season of R S at a reference temperature and related it to concurrent data of gross primary productivity at ecosystem level (GPP), light (PPFD), air temperature (Tair), orchard net primary productivity (NPP) and root growth rate. Several of these factors were then incorporated into a model to estimate R S . Data showed that temperature alone explained less than 50 % of R S variability at yearly scale. GPP, NPP, PPFD and Tair were correlated to R S at a reference temperature. The contribution of root respiration to R S increased with increasing photosynthetic activity, total tree and root growth, PPFD and Tair. On a diurnal scale, the time lag between the pattern of GPP and the pattern of R R was between 2.5 and 3 h during the growing season, decreasing to 1.5 after fruit harvest. Including GPP, NPP, PPFD and Tair to a temperature-based model improved its predicting power of R S . The results confirm the existence of a tight coupling between plant metabolism and root-derived soil respiration in the apple orchard. © 2015 Elsevier Masson SAS. All rights reserved. 1. Introduction The emission of carbon dioxide (CO 2 ) from soil is the major ecosystem carbon flux after photosynthesis [1]. This flux can origin from plant roots and their associated organisms (root respiration, R R ) or can be produced by soil microorganisms decomposing the soil organic matter (heterotrophic respiration, R H ). It has been highlighted that the sharp separation of these two components is actually an artifact because of the important role of rhizospheric microorganisms to soil respiration (i.e. heterotrophic respiration, but associated with roots). However, this conceptual splitting is useful in ecological research to study the factors controlling these processes [2e4]. Temperature is used as the primary driver to model soil respi- ration. Many equations have been developed over the years to relate these two variables [5], the two most common likely being the exponential function known as Q 10 and the Arrhenius-derived Lloyd and Taylor [6]. Both models estimate two parameters repre- senting the respiration flux at a fixed temperature (known as basal respiration, BR, in the exponential model, and as Rref, in the Arrhenius-derived model) and the sensitivity of respiration to temperature changes (known as Q 10 and E 0 , respectively). Both models, although very effective under the climatic conditions observed in many ecosystems, suffer of the drawback of predicting an indefinite increase of CO 2 flux with increasing temperature [5], an effect which is highly unlikely due to the existence of temper- ature optima for all organisms, exceeded which the inhibition of vital functions, including respiration, can be observed [7,8]. In addition, both models display the downside of relating the respi- ration flux to temperature only, a convenient, but insufficient * Corresponding author. E-mail address: francesca.scandellari@unibz.it (F. Scandellari). Contents lists available at ScienceDirect European Journal of Soil Biology journal homepage: http://www.elsevier.com/locate/ejsobi http://dx.doi.org/10.1016/j.ejsobi.2015.07.006 1164-5563/© 2015 Elsevier Masson SAS. All rights reserved. European Journal of Soil Biology 70 (2015) 77e87