Short-term Photosynthetic Responses of the C₃-CAM Epiphyte Guzmania monostachia var. monostachia to Tropical Seasonal Transitions Under Field Conditions

Abstract

A study was undertaken to investigate the rapid adaptation of photosynthesis which accompanies the tropical seasonal transition for the C₃-CAM epiphyte Guzmania monostachia (L.) Rusby ex Mez var. monostachia. In the rainy season, exposed and semi-exposed plants exhibit C₃ photosynthesis, together with sustained reductions in F_vF_m, dependent on incident light levels. At the onset of the dry season, an efficient photoprotective unit is induced within 5 days. CAM activity augments CO₂ supply and maintains sinks for electron transport. Strongly expressed photoinhibition is associated with very high levels of zeaxanthin formation. As incident light increases, total chlorophyll will decrease by around 50% in 5 days. These photoprotective functions are reversible over the same period at the start of the rainy season. The integrated response maximises productivity in the favourable rainy season and maintains photosynthetic integrity through the short adverse dry season. Such a strategy optimises carbon gain for these slow growing plants where longevity is critical for survival in the resource limited, epiphytic niche.