Bryophyte photosynthesis in sunflecks: greater relative induction rate than in tracheophytes

Photosynthetic kinetics in changing light intensity is considered pivotal for the survival of understorey tracheophytes; however, it is virtually unknown for bryophytes because bryophytes and tracheophytes have contrasting physio-ecological strategies. Anatomy suggests that relative rate of photosynthetic induction is faster in bryophyte gametophytes due to the absence of stomata, whose slow response may limit photosynthesis of tracheophyte leaves in changing light intensity. We measured steady-state and dynamic CO2 exchange in 10 bryophyte species. We performed an in-depth survey of the moss Hypnum cupressiforme sampled from sun and shade sites. Our key results are: (1) Bryophyte photosynthesis after dark acclimatisation induced much faster than in tracheophytes, reaching 50% of maximum gross photosynthesis (Agross) in about 90 s. Such rapid induction is comparable only to tracheophytes whose stomata do not limit CO2 uptake. Times to reach 90% of Agross were also substantially shorter in bryophytes (ca 220 s) than those reported for most tracheophytes (500–2000 s). (2) Shade-grown mosses did not reveal lower photosynthetic capacity than sun ones. (3) Shade-grown H. cupressiforme induced photosynthesis slightly faster than that from forest gaps. We conclude that bryophytes are efficient utilizers of temporal light heterogeneity, increasing carbon gain during short high-light events such as sunflecks in forest understorey.