Response to Smith's comment
Journal of Plant Ecology
A commentary on our recent article on Journal of Plant Ecology (Liang et al. 2013) by Smith (2014) argues that it is not appropriate to lump data from different experiments together to demonstrate the thermal acclimation of leaf dark respiration. We agree that many factors, as listed by Smith (2014) , would impact the responses of leaf carbon exchanges to warming and the consequent thermal acclimation. Although not all factors were included, we discussed in the article that light and vapor
... ure deficit (VPD) could have affected our conclusions (Liang et al. 2013). The "acclimation" in our paper did not exactly accord with the physiological definition (Atkin and Tjoelker 2003; Smith and Dukes 2013). It is hard to make the environmental factors as well as warming magnitude coherent in a synthesis study because the data were from different experiments. Therefore, the "acclimation" in our meta-analysis was more like an apparent one rather than the physiologically intrinsic one as defined by Atkin et al. (2005) and Smith and Dukes (2013). In fact, the changes in the responses of dark respiration to warming over time were the combined consequence of warming and the associated changes in environmental factors and plants themselves. Therefore, it is possible that the lower responses of dark respiration under prolonged exposure time resulted from (i) physiological acclimation of leaves, especially newly developed leaves under warming (Atkin and Tjoelker 2003; Campbell et al. 2007; Loveys et al. 2003), and (ii) the lower water availability, substrate availability and/or higher VPD, which usually accompany climate warming (Atkin and Tjoelker 2003; Barber et al. 2000; Joseph et al. 2014; Xie et al. 2010). Overall, our meta-analysis demonstrated that the response of leaf dark respiration was likely to be lower if the climate warming continues. In other words, the apparent thermal acclimation would occur after a long-term warming. The reason could be the physiological acclimation, or other environmental constraints, or their combination. We agree with Smith (2015) that the intrinsic thermal acclimation of plant leaf carbon exchange is difficult to examine by the traditional meta-analysis such as Liang et al. (2013). It would be valuable that future research clearly clarifies whether the intrinsic or apparent thermal acclimation is studied. rEFErENCEs Atkin OK, Bruhn D, Hurry VM, et al. (2005) The hot and the cold: unravelling the variable response of plant respiration to temperature. Funct Plant Biol 32:87-105. Atkin OK, Tjoelker MG (2003) Thermal acclimation and the dynamic response of plant respiration to temperature. Trends Plant Sci 8:343-51. Barber VA, Juday GP, Finney BP (2000) Reduced growth of Alaskan white spruce in the twentieth century from temperature-induced drought stress. Nature 405:668-73. Campbell C, Atkinson L, Zaragoza-Castells J, et al. (2007) Acclimation of photosynthesis and respiration is asynchronous in response to changes in temperature regardless of plant functional group. New Phytol 176:375-89. Joseph T, Whitehead D, Turnbull MH (2014) Soil water availability influences the temperature response of photosynthesis and respiration in a grass and a woody shrub. Funct Plant Biol 41:468-81. Liang JY, Xia JY, Liu LL, et al. (2013) Global patterns of the responses of leaf-level photosynthesis and respiration in terrestrial plants to experimental warming. J Plant Ecol 6:437-47. Loveys BR, Atkinson LJ, Sherlock DJ, et al. (2003) Thermal acclimation of leaf and root respiration: an investigation comparing inherently fast-and slow-growing plant species. Global Change Biol 9:895-910. Smith NG (2015) Testing for temperature acclimation of plant carbon exchange: a comment on "Global patterns of the responses of leaflevel photosynthesis and respiration in terrestrial plants to experimental warming". J Plant Ecol 8:335-6. Smith NG, Dukes JS (2013) Plant respiration and photosynthesis in global-scale models: incorporating acclimation to temperature and CO 2 .