Contents lists available at ScienceDirect Ecological Indicators journal homepage: www.elsevier.com/locate/ecolind Original Articles Leaf δ 13 C as an indicator of water availability along elevation gradients in the dry Himalayas Rita Ale a,b , Lin Zhang a,e , Xiang Li a,b , Bhakta Bahadur Raskoti c , Francisco I. Pugnaire d , Tianxiang Luo a,e, ⁎ a Key Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China b University of Chinese Academy of Sciences, Beijing 100049, China c State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China d Estación Experimental de Zonas Áridas, Consejo Superior de Investigaciones Científicas, Almería, Spain e CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China ARTICLE INFO Keywords: Alpine ecosystem Carbon isotope Dry mountains Moisture index Precipitation ABSTRACT Understanding the variation of water availability along elevation gradients is essential for predicting the re- sponse of mountain ecosystems to global warming. However, it is challenging to precisely quantify water availability in dry mountains, especially in remote areas where climate records are limited. In dry habitats, leaf δ 13 C is highly sensitive to water availability. Here, we demonstrated how leaf δ 13 C of a widespread species could be used as an indicator of water availability in dry mountainous regions. We measured leaf δ 13 C and nitrogen content in one dominant forb and two cushion species along two elevational transects in the central Himalayas, Nepal. The Thornthwaite climatic moisture index was determined for each elevation site based on the 1-km 2 WorldClim data of monthly mean temperature and precipitation. We found that the elevational variation of δ 13 C in each of the three species was associated with precipitation, in which growing-season moisture index and annual precipitation were negatively correlated with δ 13 C, regardless of elevation and temperature. Elevation and leaf nitrogen showed no significant relationship with leaf δ 13 C. Thus, within-species leaf δ 13 C promises to be a simple and reliable indicator of environmental severity along elevation gradients, which can be easily quan- tified in remote high-mountain environments. Leaf δ 13 C would be a useful predictor of the change in water availability induced by warming in dry mountainous regions like the Himalayas. 1. Introduction Water availability is one of the most crucial factors determining species distribution and ecosystem functioning along elevation gra- dients in dry mountains (Cavieres et al., 2006; Wang et al., 2013; Pugnaire et al., 2015; Winkler et al., 2016). It has been shown that soil water availability plays a significant role in driving plant productivity (Wang et al., 2013; Ernakovich et al., 2014; Winkler et al., 2016) and plant-plant interactions (Cavieres et al., 2006; Armas et al., 2011; Pugnaire et al., 2015) as well as altering the timing of phenological events in alpine ecosystems (Ernakovich et al., 2014; Li et al., 2016). Therefore, understanding how water availability changes along eleva- tion gradients is essential for predicting the response of mountain ecosystems to ongoing climate change (Wang et al., 2013; Pugnaire et al., 2015). However, an elevational pattern of soil water availability cannot be generally defined because precipitation (the main driver of soil water availability) shows variable patterns with elevation, mostly depending on regional topography and local climate system (Körner, 2007; McCain and Grytnes, 2010). In addition, water availability in high mountains can be further confounded by temperature, soil texture, soil depth, snow cover and snow melting time (Williams et al., 2009). It is thus challenging to precisely quantify water availability in dry mountains, especially in remote areas where climate records are scarce. Thus, identifying simple and reliable indicators of water availability is important for understanding patterns of species distribution and eco- system functioning along elevation gradients in dry mountain regions. In C 3 plants, stable carbon isotope composition in leaves (δ 13 C) can provide an integrated measurement of internal–physiological and ex- ternal–environmental conditions during the growing season (Farquhar et al., 1989; Dawson et al., 2002). Leaf δ 13 C is primarily related to the ratio of intercellular (C i ) to atmospheric (C a ) partial pressure of CO 2 (C i /C a ; Farquhar et al., 1989). The balance of this ratio is highly https://doi.org/10.1016/j.ecolind.2018.07.002 Received 12 July 2017; Received in revised form 29 June 2018; Accepted 1 July 2018 ⁎ Corresponding author at: Key Laboratory of Alpine Ecology and Biodiversity, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Building 3, 16 Lin Cui Rd., Chaoyang District, Beijing 100101, China. E-mail address: luotx@itpcas.ac.cn (T. Luo). Ecological Indicators 94 (2018) 266–273 1470-160X/ © 2018 Elsevier Ltd. All rights reserved. T