Seasonal and temperature dependence of photosynthesis and respiration for two co-occurring broad-leaved tree species with contrasting leaf phenology.

Abstract

We measured the seasonal and temperature responses of leaf photosynthesis and respiration of two co-occurring native New Zealand tree species with contrasting leaf phenology: winter-deciduous fuchsia (Fuchsia excorticata J. R. Forst & G. Forst) and annual evergreen wineberry (Aristotelia serrata J. R. Forst & G. Forst). There was no difference in the amount of nitrogen per unit leaf area (N_area, range 40–160 mmol m⁻², P = 0.18) or specific leaf area (S, range 8–27 m² kg⁻¹, P = 0.87) in summer leaves of wineberry or fuchsia. The amount of nitrogen per unit leaf area and S varied significantly with height of leaves in the canopy for both species (r² range 0.61–0.87). Parameters describing the maximum rates of rubisco carboxylation (V_cmax) and electron transport (J_max) were related significantly to N_area, and were 60% higher on average in spring and summer leaves than in autumn and winter leaves for both species. The seasonal effect remained significant (P < 0.001) when N_area was included in a regression model, indicating that seasonal changes were not only due to changes in N_area. Values for V_cmax and J_max were 30% lower in wineberry leaves than in fuchsia leaves on average, although the difference ranged from 15% in summer leaves to 39% in autumn leaves. Activation energies describing the temperature dependence of V_cmax and J_max in wineberry were 111 and 114% of corresponding values for fuchsia (E_a (V_cmax) = 39.1 kJ mol⁻¹, E_a (J_max) = 32.9 kJ mol⁻¹). Respiration at night was the same (P = 0.34) at 10 °C for both species (R₁₀ = 0.7 μmol m⁻² s⁻¹), although activation energies (E₀) were higher in wineberry than in fuchsia (47.4 and 32.9 kJ mol⁻¹ K⁻¹, respectively). These results show that rates of photosynthesis are higher in winter-deciduous fuchsia than in annual evergreen wineberry.