Seasonal changes in photosynthetic pigment composition of aquatic bryophytes

Resumen

The seasonal changes in photosynthetic pigment composition of 13 aquatic bryophytes from diverse habitats were analyzed. Chlorophyll contents (2.2-9.2 mg g−1 dry weight and 97-351 mg m−2 shoot area) were higher than those of terrestrial bryophytes, lower than in cormophytes but comparable to epilithic river algae. Chlorophyll alb ratios (2.1-2.8) and a carotenoid index, OD430/0D665 (1.72-2.11), were significantly lower than in cormophytes. This is interpreted as an adaptation to shade conditions and to lower physiological activity than in cormophytes. Phaeopigment content showed a positive correlation with chlorophyll content, because of the presence of a functional phaeophytin a in photosystem II, but chlorophyll degradation in emersed bryophytes occurred without producing phaeopigments. Phaeopigment ratios varied little with season or habitat. Leaf specific area and leaf specific weight, comparable to those in terrestrial bryophytes, were indicative of the proportion of non-photosynthetic tissues and desiccation-and-light tolerance of the different species.The clearest seasonal pigment cycles were shown by species experiencing summer desiccation. In summer they showed strong decreases in chlorophyll content and chlorophyll a/b ratio, and an increase in carotenoids/chlorophylls ratio. Continuously wet bryophytes showed more attenuated seasonal cycleswhich correlated with changes in light conditions (primarily canopy state). In most permanently immersed species in sun-exposed habitats, chlorophyll content and chlorophyll a/b ratio were high in all seasons indicating high metabolic activity throughout the year. Continuously hydrated and especially submerged species exhibited the smallest seasonal pigment variations