Impact of growth temperature on scaling relationships linking photosynthetic metabolism to leaf functional traits

Scaling relationships linking photosynthesis (A) to leaf traits are important for predicting vegetation patterns and plant-atmosphere carbon fluxes. Here, we investigated the impact of growth temperature on such scaling relationships. We assessed whether changes in growth temperature systematically altered the slope and/or intercepts of log-log plots of A vs leaf mass per unit leaf area (LMA), nitrogen and phosphorus concentrations for 19 contrasting plant species grown hydroponically at four temperatures (7, 14, 21 and 28 °C) in controlled environment cabinets. Responses of 21 °C-grown pre-existing (PE) leaves experiencing a 10 day growth temperature (7, 14, 21 and 28 °C) treatment, and newly-developed (ND) leaves formed at each of the four new growth temperatures, were quantified. Irrespective of the growth temperature treatment, rates of light-saturated photosynthesis (A) were measured at 21 °C. Changes in growth temperature altered the scaling between A and leaf traits in pre-existing (PE) leaves, with thermal history accounting for up to 17% and 31% of the variation on a mass and area basis, respectively. However, growth temperature played almost no role in accounting for scatter when comparisons were made of newly-developed (ND) leaves that form at each growth temperature. Photosynthetic nitrogen and phosphorus use efficiency (PNUE and PPUE, respectively) decreased with increasing LMA. No systematic differences in temperature-mediated reductions in PNUE or PPUE of PE leaves were found among species. Overall, these results highlight the importance of leaf development in determining the effects of sustained changes in growth temperature on scaling relationships linking photosynthesis to other leaf traits.