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White birch (Betula papyrifera Marsh.) seedlings were grown under two carbon dioxide concentrations (ambient: 360 μmol mol−1 and elevated: 720 μmol mol−1), three soil temperatures (5, 15 and 25 °C initially, increased to 7, 17 and 27 °C, respectively, 1 month later) and three moisture regimes (low: 30–40%; intermediate: 45–55% and high: 60–70% field water capacity) in greenhouses. In situ gas exchange and chlorophyll fluorescence were measured after 2 months of treatments. Net photosynthetic rate (An) of seedlings grown under the intermediate and high moisture regimes increased from low to intermediate Tsoil and then decreased to high Tsoil. There were no significant differences between the low and high Tsoil, with the exception that An was significantly higher under high than low Tsoil at the high moisture regime. No significant Tsoil effect on An was observed at the low moisture regime. The intermediate Tsoil increased stomatal conductance (gs) only at intermediate and high but not at low moisture regime, whereas there were no significant differences between the low and high Tsoil treatments. Furthermore, the difference in gs between the intermediate and high Tsoil at high moisture regime was not statistically significant. The low moisture regime significantly reduced the internal to ambient CO2 concentration ratio at all Tsoil. There were no significant individual or interactive effects of treatment on maximum carboxylation rate of Rubisco, light-saturated electron transport rate, triose phosphate utilization or potential photochemical efficiency of photosystem II. The results of this study suggest that soil moisture condition should be taken into account when predicting the responses of white birch to soil warming. [ABSTRACT FROM PUBLISHER]

To investigate the interactive effects of atmospheric carbon dioxide concentration ([CO2]) and nutrition on photosynthesis and its acclimation to elevated [CO2], a two-way factorial experiment was carried out with two nutritional regimes (high- and low-nitrogen (N), phosphorus (P) and potassium (K)) and two CO2 concentrations (360 and 720 ppm) with white birch seedlings (Betula papyrifera Marsh.) grown for four months in environment-controlled greenhouses. Elevated [CO2] enhanced maximal carboxylation rate (Vcmax), photosynthetically active radiation-saturated electron transport rate (Jmax), actual photochemical efficiency of photosystem II (PSII) in the light (ΔF/Fm′) and photosynthetic linear electron transport to carboxylation (Jc) after 2.5 months of treatment, and it increased net photosynthetic rate (An), photosynthetic water-use efficiency (WUE), photosynthetic nitrogen-use efficiency (NUE) and photosynthetic phosphorus-use efficiency (PUE) after 2.5 and 3.5 months of treatment, but it reduced stomatal conductance (gs), transpiration rate (E) and the fraction of total photosynthetic linear electron transport partitioned to oxygenation (Jo/JT) after 2.5 and 3.5 months of treatment. Low nutrient availability decreased An, WUE, Vcmax, Jmax, triose phosphate utilization (TPU), (/Fm′ – F)//Fm′ and Jc, but increased Jo/JT and NUE. Generally, Vcmax was more sensitive to nutrient availability than Jmax. There were significant interactive effects of [CO2] and nutrition over time, e.g., the positive effects of high nutrition on An, Vcmax, Jmax, ΔF/Fm′ and Jc were significantly greater in elevated [CO2] than in ambient [CO2]. In contrast, the interactive effect of [CO2] and nutrition on NUE was significant after 2.5 months of treatment, but not after 3.5 months. High nutrient availability generally increased PUE after 3.5 months of treatment. There was evidence for photosynthetic up-regulation in response to elevated [CO2], particularly in seedlings receiving high nutrition. Photosynthetic depression in response to low nutrient availability was attributed to biochemical limitation (or increased mesophyll resistance) rather than stomatal limitation. Elevated [CO2] reduced leaf N concentration, particularly in seedlings receiving low nutrition, but had no significant effect on leaf P or K concentration. High nutrient availability generally increased area-based leaf N, P and K concentrations, but had negligible effects on K after 2.5 months of treatment. [ABSTRACT FROM AUTHOR]