RESEARCH PAPER Responses of leaf nitrogen and mobile carbohydrates in different Quercus species ⁄ provenances to moderate climate changes M.-H. Li 1 , P. Cherubini 1 , M. Dobbertin 1 , M. Arend 1 , W.-F. Xiao 2 & A. Rigling 1 1 Swiss Federal Research Institute WSL, Birmensdorf, Switzerland 2 Research Institute of Forest Ecology, Environment and Protection, Chinese Academy of Forestry, Beijing, China INTRODUCTION Over the past 100 years, the global average temperature has increased by approximately 0.6 °C (±0.2 °C) and is projected to continue to rise at a rapid rate (IPCC 2007). Increasing temperatures will lead to corresponding changes in the amount and type of precipitation. In Central Europe, the summer temperatures are expected to increase by another 1.9–7.0 °C, and the amount of summer precipitation to decrease by 9–41% until 2070 (Frei 2004; Scha ¨r et al. 2004). Such climate change will inevitably have considerable impact on plant physiology, growth, productivity and forest ecosys- tem functions (Ko ¨rner 2000; Li et al. 2006). There have been critical evaluations and strong overtones throughout on the role of the principal climatic and edaphic factors that influence growth through the intermediation of internal bio-physicochemical processes such as photosynthesis (Kozlowski 1962) and carbon balance (Ko ¨rner 2003). For example, temperature influences rates of photosynthesis and respiration, as well as growth rate associated with rates of cell division and elongation. Water deficit has been shown to affect various physiological and biochemical processes in plants. For example, drought was found to influence the metabolism of soluble carbohydrates (Hanson & Hitz 1982; Smirnoff 1993; Chaves et al. 2003; Reddy et al. 2004). Levels of soluble sugars and starch reflect the balance between car- bon gain (photosynthesis) and loss (growth and maintenance respiration) within a plant, representing a tree’s capital for growth after dormancy and acting as a buffer for insufficient source activity (photosynthesis) due to adverse weather con- ditions or loss of foliage (Li et al. 2002; Hoch et al. 2003; Ko ¨rner 2003). Most of the carbohydrates formed during pho- tosynthesis are used as substrate for respiration to provide the energy needed for growth and maintenance processes. Nonetheless, part of the synthesised carbohydrates can tran- siently be stored as starch, while soluble sugars might serve as osmolytes during water stress (Kozlowski 1992; Pallardy 2008). Oaks (Quercus spp.) are ecologically and economically important woody plants that are widely distributed from temperate deciduous forests to the montane tropics (Morris et al. 2008). Quercus robur and Q. petraea represent the most Keywords Adaptation; drought; environmental changes; global warming; non-structural carbohydrates; oak; soluble sugars; starch. Correspondence M.-H. Li, Swiss Federal Research Institute WSL, Zuercherstrasse 111, CH-8903 Birmensdorf, Switzerland. E-mail: maihe.li@wsl.ch Editor M. Gu ¨ nthardt-Goerg Received: 7 December 2011; Accepted: 3 February 2012 doi:10.1111/j.1438-8677.2012.00579.x ABSTRACT Global warming and shortage of water have been evidenced in the recent past and are predicted for the future. Climate change will inevitably have considerable impact on plant physiology, growth, productivity and forest ecosystem functions. The present study determined the effects of simulated daytime air warming (+1 to 1.5 °C during the growing season), drought ()40% and )57% of mean precipitation of 728 mm during the 2007 and 2008 growing season, respectively) and their combi- nation, on leaf nitrogen (N) and non-structural carbohydrates (NSC) of two Quer- cus species (Q. robur and Q. petraea) and provenances (two provenances for each species) grown in two soil types in Switzerland across two treatment years, to test the hypothesis that leaf N and NSC in the more water-sensitive species (Q. robur) and provenances (originating from water-rich locations) will more strongly respond to global warming and water deficit, compared to those in the more drought-toler- ant species (Q. petraea) or provenances. No species- and provenance-specific responses in leaf N and NSC to the climate treatment were found, indicating that the results failed to support our hypothesis. The between-species variation of leaf N and NSC concentrations mainly reflected differences in biology of the two species, and the between-provenance variation of N and NSC concentrations apparently mirrored the climate of their origins. Hence, we conclude that (i) the two Quercus species studied are somewhat insensitive, due to their distribution covering a wide geographical and climate range, to moderate climate change within Switzerland, and (ii) a moderate global warming of B1 scenario (IPCC 2007) will not, or at least less, negatively affect the N and carbon physiology in Q. robur and Q. petraea. Plant Biology ISSN 1435-8603 Plant Biology ª 2012 German Botanical Society and The Royal Botanical Society of the Netherlands 1