Leaf physiological response to light environment of three tree fern species in a Mexican cloud forest

Abundance and physiology of three understorey tree fern species were compared in a Mexican cloud forest. We hypothesized that the distribution of species would be associated with canopy openness and leaf physiological characteristics. In gullies(1-2% full sun), Alsophila firma was abundant, Cyathea divergens was distributed in moderately open places (4-9%), and Lophosoria quadripinnata preferred more open canopy (9-30%). Although 11 leaf traits of five plants of each species growing under closed and open canopies over 1 y did not differ within species, there were significant interspecific differences. Alsophila firma had comparatively low maximum electron transport rate ETRmax (26.8 +/- 1.81 mu mol m(-2) s(-1)) and ETR light saturation point (ETRLSP: 261 +/- 36.1 mu mol m(-2) s(-1)), high specific leaf area (SLA), thin leaves and decreased quantum yield during a leaf desiccation experiment. Cyathea divergens had relatively high maximum quantum yield (0.84 +/- 0.004), ETRmax (37.3 +/- 1.8 mu mol m(-2) s(-1)) and ETRLSP (409 +/- 40.0 mu mol m(-2) s(-1)). Lophosoria quadripinnata had comparatively thick leaves, low SLA, high predawn water potential, high density (606 +/- 25.5 mm(-2)) and small length (0.026 +/- 0.002 mm) stomata. The results support the hypothesis that light sensitivity shapes tree fern distribution in the cloud forest.