Contents lists available at ScienceDirect Ecological Indicators journal homepage: www.elsevier.com/locate/ecolind Development of digital photographic approaches to assess leaf traits in broadleaf tree species Francesco Chianucci a, ⁎ , Carlotta Ferrara a , Martina Pollastrini b , Piermaria Corona a a Consiglio per la ricerca in agricoltura e l’analisi dell’economia agraria – Research Centre for Forestry and Wood, Viale Santa Margherita 80, Arezzo, Italy b University of Florence, Department of Agriculture, Food, Environment and Forestry, Piazzale delle Cascine 18, Firenze, Italy ARTICLE INFO Keywords: Leaf optical properties Functional leaf traits Leaf reflectance Foliar morphology Foliar physiology ABSTRACT Plants display a large number of traits which are reflected in physiological and ecological functions (functional traits). Leaf traits are amongst the most important functional traits. However, a great challenge in measuring leaf traits in the field is that direct methods are limited by the cost of the instruments and the time and work required by direct measurements, which are often destructive. As an alternative, we developed and tested a non-de- structive methodology to assess a suite of leaf traits using different digital photographic approaches, with the intimate aim to develop a rapid, robust and cheap protocol for leaf trait measurements in the field. The proposed digital photographic approaches were tested in broadleaved tree species Digital photography allowed to assess a morphological foliar trait (leaf area; LA) and physiological foliar traits (leaf reflectance in red (R), green (G) and blue (B) bands; leaf venation attributes). Leaf area derived from photography significantly agreed with that directly measured with a leaf area meter (LA PHOTO = 0.98 LA AREA METER + 0.84, R 2 =0.99, p < 0.001); leaf reflectance in the R, G, B channels derived from photography significantly agreed with that directly measured with a field spectroradiometer (SPEC) (R PHOTO = 0.77 R SPEC + 0.05, R 2 =0.61, p < 0.001; G PHOTO =0.79 G SPEC + 0.06, R 2 =0.58, p < 0.001; B PHOTO = 0.56 B SPEC + 0.00, R 2 =0.51, p < 0.001). Leaf venation traits estimated from photography agreed to within ± 20% measurements obtained in cleared leaves of the same species. Based on the obtained results, we demonstrated that digital photography can be an effective tool to obtain a fast, cheap, reliable and non-destructive assessment of morphological and physiological leaf traits in broadleaf tree species, being highly suitable for use in long-term research and monitoring programs. 1. Introduction Plants display a large number of traits which are reflected in phy- siological and ecological functions (functional traits). The amplitude with which certain traits vary within the same species determines its ability to acclimate to standing environmental conditions and to adapt to climate change (Valladares et al., 2007; Grotti et al., 2019; McMurtrie and Deawr (2011); Walters and Gerlach, 2013; Lilles et al., 2014; Coble et al., 2016). Leaf traits are amongst the most important plant functional traits since leaves are the primary drivers of light in- terception and photosynthesis within plant canopies. Plants may en- hance whole canopy light interception by varying foliar morphology, physiology and phenology (Niinemets and Kull, 1999; Niinemets and Fleck, 2002; Blonder et al., 2011; Chianucci et al., 2018). Leaf traits are directly related to photosynthesis and can be used to monitor the in- fluence of biotic and abiotic environmental stress on plant physiology and growth. Leaf size parameters, like leaf area (LA) and specific leaf area (SLA), are important ecological indicators ‘per se’, since many environmental stress factors reduce the development of individual plant organs (i.e. leaves) and the growth of the whole plant. Drought stress and low nutrient availability, high solar radiation and extreme (high/ low) temperatures reduce LA and SLA (Azeñas et al., 2019; Leuschner and Meier, 2018; Marron et al., 2003; Pérez-Harquindeguy et al., 2013; Reich et al., 1998). These traits also influence the light and water balance of the leaves and then of the whole crown of the plant. Phy- siological leaf traits, like leaf reflectance and leaf venation attributes, are indicative of the resource use efficiency of the plants (Cotrozzi et al., 2017). Leaf reflectance is a leaf optical feature affecting the solar ra- diation absorption capacity and then the leaf photosynthetic rate. On the other hand, the structure and density of the leaf venation are es- sential for the water use efficiency within leaf tissue, affecting the leaf water balance (Scoffoni et al., 2011). Leaf traits are also connected to forest ecosystem services, such as carbon sequestration, pollutants re- moval and climate regulation (Sedjo and Sohngen, 2012). https://doi.org/10.1016/j.ecolind.2019.105547 Received 19 April 2019; Received in revised form 27 June 2019; Accepted 3 July 2019 ⁎ Corresponding author. E-mail addresses: fchianucci@gmail.com, francesco.chianucci@crea.gov.it (F. Chianucci). Ecological Indicators 106 (2019) 105547 1470-160X/ © 2019 Elsevier Ltd. All rights reserved. T