Nitrogen availability affects the ecophysiological responses of amur linden and white birch to CO2 and temperature

Abstract

Climate change, e.g., elevated CO₂, warmer temperature, and nitrogen (N) deposition, can have substantial effects on tree physiology and growth. This study explored the effects of future CO₂ and temperature (fCT, representative of future climate conditions) on the growth and photosynthetic traits of amur linden and white birch seedlings under different N availability. The results showed that fCT significantly increased the total seedling biomass and total seedling leaf area of amur linden and white birch synergistically with increasing nitrogen supply. However, the specific leaf area (leaf area to leaf mass ratio) of amur linden was significantly reduced by the two treatments. Increases in N availability alleviated the photosynthetic downregulation associated with fCT as indicated by the photosynthetic capacity parameters of V_cmax and J_max. Our results indicate that the primary limitation of photosynthesis under fCT in the two species will likely shift from Rubisco carboxylation to RuBP regeneration. However, the rate of photosynthesis was significantly higher under the fCT than control conditions in amur linden but was not significantly different between the two treatment conditions in white birch, indicating that the photosynthetic downregulation completely offset the positive effect of increased CO₂ on photosynthesis in white birch. Our results suggest that the relative performance and competitiveness of the two species may be very different in future, and more detailed studies are warranted on the responses of the two species to climate change.