The photosynthetic response of eight species of Acer to simulated light regimes from the centre and edges of gaps

Abstract

1. Seedlings of eight Acer species grown under two light treatments simulating forest gap edge (photosynthetic photon flux density, PPFD=30μmolm–2s–1; R:FR=0·6) and gap centre (PPFD=400μmolm–2s–1; R:FR=1·1) were studied to explore the effect of growth irradiance on transient‐ and steady‐state photosynthesis. 2. The increase in maximum photosynthetic rate (Amax) from gap edge‐ to gap centre‐grown seedlings ranged between 20% in Acer saccharum and 138% in Acer ginnala. Amax differed significantly among species (2·3 to 12·3μmolm–2s–1) but assimilation rates under dim light (30μmolm–2s–1) were more similar (0·6 to 1·4μmolm–2s–1). 3. Significant differences among species in stomatal conductance indicate that species of high photosynthetic performance maintain higher dim light conductance and show a much greater excursion in stomatal opening under saturating light. 4. Lightfleck response based on actual photosynthetic rates was more rapid in gap centre‐ vs gap edge‐grown plants but the latter demonstrated more rapid rates of photosynthetic induction (PI). 5. We suggest that the estimation of photosynthetic induction state is prone to an inverse relationship with maximum photosynthetic rate (Amax) and so may not be directly related to efficiency in sunfleck response. Conversely, higher Amax can result in low PI but is also associated with higher transient rates of assimilation during a lightfleck and, therefore, be equally relevant as induction properties. 6. It appears that leaves with characters such as greater specific leaf mass and area‐based leaf N, even within the same irradiance treatment, may confer a carboxylation advantage to sunfleck utilization not reflected in PI. However, whether the total carbon return on such a leaf is better assessed by PI or transient photosynthetic rate remains to be determined.