CO2 elevation improves photosynthetic performance in progressive warming environment in white birch seedlings

Abstract

White birch (Betula paperifera Mash) seedlings were exposed to progressively warming in greenhouses under ambient and elevated CO2 concentrations for 5 months to explore boreal tree species’ potential capacity to acclimate to global climate warming and CO2 elevation. In situ foliar gas exchange, in vivo carboxylation characteristics and chlorophyll fluorescence were measured at temperatures of 26oC and 37oC. Elevated CO2 significantly increased net photosynthetic rate (Pn) at both measurement temperatures, and Pn at 37oC was higher than that at 26oC under elevated CO2. Stomatal conductance (gs) was lower at 37oC than at 26oC, while transpiration rate (E) was higher at 37oC than that at 26oC. Elevated CO2 significantly increased instantaneous water-use efficiency (WUE) at both 26oC and 37oC, but WUE was markedly enhanced at 37oC under elevated CO2. The effect of temperature on maximal carboxylation rate (Vcmax), PAR-saturated electron transport rate (Jmax) and triose phosphate utilization (TPU) varied with CO2, and the Vcmax and Jmax were significantly higher at 37oC than at 26oC under elevated CO2. However, there were no significant interactive effects of CO2 and temperature on TPU. The actual photochemical efficiency of PSII (DF/ Fm’), total photosynthetic linear electron transport rate through PSII (JT) and the partitioning of JT to carboxylation (Jc) were higher at 37oC than at 26oC under elevated CO2. Elevated CO2 significantly suppressed the partitioning of JT to oxygenation (Jo/JT). The data suggest that the CO2 elevation and progressive warming greatly enhanced photosynthesis in white birch seedlings in an interactive fashion.