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Predicting the future distribution of plants requires a mechanistic understanding of how plants cope with their new environmental conditions under a changed climate. We examined the effects of elevated carbon concentration ([CO2]) and elevated Tsoil on the physiological responses to light of a shade-tolerant woody species, mountain maple (Acer spicatum L.). Seedlings were exposed to ambient and elevated [CO2] (392μmolmol−1 vs. 784μmolmol−1), current and elevated soil temperatures (Tsoil 17 vs. 22°C) at high and low (100% vs. 30%) light conditions for one growing season. It was found that elevated Tsoil stimulated net photosynthesis (A) by 18% in the low-light treatment but tended to reduce A in the high-light treatment. Elevated [CO2] increased A by 100% under the elevated Tsoil and by 48% at the current Tsoil. The effect of elevated Tsoil also varied with [CO2]: it increased A by 13% under the elevated [CO2] but reduced A by 17% under the ambient [CO2]. We observed a significant increase in the instantaneous water-use efficiency of photosynthesis (IWUE) in response to the high-light treatment under the elevated [CO2] but not under the ambient [CO2]. Our data indicate that the elevated [CO2] markedly increased nitrogen (N) allocation to the photochemical apparatus of A in seedlings grown under the high-light condition. These results suggest that the predicted increases in atmospheric [CO2] will likely enhance the growth of mountain maple in canopy gaps in the forest, while the predicted elevated Tsoil will negate the benefit of high-light conditions. [ABSTRACT FROM AUTHOR]

Global climate change is expected to affect how plants respond to their physical and biological environments. In this study, we examined the effects of elevated CO2 ([CO2]) and low soil moisture on the physiological responses of mountain maple (Acer spicatum L.) seedlings to light availability. The seedlings were grown at ambient (392 µmol mol−1) and elevated (784 µmol mol−1) [CO2], low and high soil moisture (M) regimes, at high light (100%) and low light (30%) in the greenhouse for one growing season. We measured net photosynthesis (A), stomatal conductance (gs), instantaneous water use efficiency (IWUE), maximum rate of carboxylation (Vcmax), rate of photosynthetic electron transport (J), triose phosphate utilization (TPU)), leaf respiration (Rd), light compensation point (LCP) and mid-day shoot water potential (Ψx). A and gs did not show significant responses to light treatment in seedlings grown at low soil moisture treatment, but the high light significantly decreased the Ci/Ca in those seedlings. IWUE was significantly higher in the elevated compared with the ambient [CO2], and the effect was greater at high than the low light treatment. LCP did not respond to the soil moisture treatments when seedlings were grown in high light under both [CO2]. The low soil moisture significantly reduced Ψx but had no significant effect on the responses of other physiological traits to light or [CO2]. These results suggest that as the atmospheric [CO2] rises, the physiological performance of mountain maple seedlings in high light environments may be enhanced, particularly when soil moisture conditions are favourable. [ABSTRACT FROM AUTHOR]

Abstract: To study the effects of source–sink ratio and nutrient supply on photosynthetic acclimation to CO2 elevation, we subjected white birch seedlings to two levels of nutrient supply (high vs. low) and CO2 concentrations (ambient vs. doubled [CO2]) for two months and then shaded the lower canopy on half of the seedlings to reduce source/sink ratio for an additional month. The CO2 elevation significantly increased P n and IWUE at both nutrient levels but the increase was greater in the high than low nutrient treatment. The CO2 elevation resulted in a down-regulation of V cmax in the low nutrient treatment but up-regulation of J max, TPU, and J c in the high nutrient after 3 months of treatment. Both the CO2 elevation and high nutrient supply increased the partition of total electron transport to carboxylation at the expense of oxidation. The seedlings responded to the shading of the lower canopy by reducing biomass allocation to roots rather than making physiological adjustments to unshaded leaves in the upper canopy. Our results suggest that the direction of photosynthetic acclimation to CO2 elevation in white birch was nutrient-dependent and an increase in sink strength could reduce the feedback inhibition of photosynthesis. [Copyright &y& Elsevier]

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]

CO2–light interactions can influence the competition among boreal plants, but are poorly understood. We investigated the effect of such interactions on the growth and biomass of 1-year-old black spruce (Sb) (Picea mariana (Mill.) BSP) and white spruce (Sw) (Picea glauca (Moench) Voss) grown with CO2 concentrations ([CO2]) of 360 and 720 µmol·mol–1 under 30%, 50%, and 100% light, in greenhouses. There were significant two-way and three-way interactions. Root collar diameter (RCD) of Sw decreased with decreasing light, while in Sb, there was no significant difference in RCD for plants grown under 50% or 30% light. Height was greater for plants grown under 100% light than if the plants were shaded. Elevated [CO2] increased RCD by 33% and enhanced stem volume by 67%, 98%, and 84% under 100%, 50%, and 30% light, respectively. The CO2 enhancement of total biomass was relatively higher under lower light, and greater for Sb than Sw. Elevated [CO2] decreased specific leaf area under 50% light only. Root mass was generally higher under 100% light than when shaded. Elevated [CO2] increased the root mass of Sb under 100% light, but decreased it under 30% light. Elevated [CO2] decreased the shoot/root ratio under 100% light, but increased it under 30% light. Our data suggest that raising [CO2] will likely increase species competitiveness under low light conditions, and that the increase will be greater in species that are relatively shade tolerant. [ABSTRACT FROM AUTHOR]

White birch ( Betula papyrifera Marsh.) seedlings were exposed to ambient or doubled ambient carbon dioxide concentration ([CO2]), three soil temperatures ( Tsoil) (low, intermediate, high), and three phosphorus (P) regimes (low, medium, high) in environment-controlled greenhouses. Height ( H), root-collar diameter (RCD), biomass, and leaf phosphorus concentration (leaf P) were determined four months after initiation of treatments. The low Tsoil reduced H, RCD, shoot biomass, root biomass and total seedling biomass whereas the high-P level and the [CO2] elevation increased all the growth and biomass parameters. Elevated [CO2] significantly reduced leaf P. There were significant two-factor interactions suggesting that the effect of elevated [CO2] on (1) H, total biomass, biomass of plant components, and leaf P was dependent on Tsoil, (2) total biomass was contingent on P regime. For instance, the positive response of H and total biomass to elevated [CO2] was limited to seedlings raised under the intermediate and high Tsoil, respectively. In addition, [CO2] elevation increased total biomass only at the high-P regime but not at the low- or medium-P level where the effect of [CO2] was statistically insignificant. No significant main effect of treatment or interaction was observed for root to shoot biomass ratio. [ABSTRACT FROM AUTHOR]