Photoinhibition of photosynthesis in Minquartia guianensis and Swietenia macrophylla inferred by monitoring the initial fluorescence

We assessed the effect of the exposure to full sunlight (5, 35, and 120 min, i.e. T₅, T₃₅, and T₁₂₀) on fluorescence parameters of two young tropical trees, Swietenia macrophylla, a gap-demanding species, and Minquartia guianensis, a shade tolerant species. Fluorescence parameters (F₀, F_m, F_v/F_m) were recorded before treatments and after the transition to low irradiance (LI). Recovery from photoinhibition (measured as F_v/F_m) was monitored for 24 h at LI. In Swietenia, an almost complete restoration of the F_v/F_m values occurred in T₅ and T₃₅ plants, when a rise in F₀ was observed after the transition to LI. This was inferred as indicative of dynamic photoinhibition. T₁₂₀ led to a decline in F₀ in Minquartia, but not in Swietenia. The plants of both species were unable to recovery from photoinhibition after 24 h at LI, when F₀ declined or remained unchanged. This was interpreted as indicative of chronic photoinhibition. Compared with Swietenia, Minquartia was more susceptible to photoinhibition, as indicated by lower F_v/F_m values.