15 Photosynthesis in Aquatic Plants
J.A. Raven
15.1 Introduction
To address the topic of the ecophysiology of photosynthesis in aquatic plants
in the space allotted is a daunting task, and the coverage must of necessity
be very selective. Since this Volume is honoring Professor Dr. Lange, I shall
emphasize those aspects which interface with his work, and since the rest of
the Volume deals with terrestrial plants, I shall emphasize more generally
the comparison with terrestrial plants. My third objective is to address
particularly those aspects which most interest me and which are, or could
be, growth-points in research.
15.2 Definition of the Aquatic Habitat
Nature's distinction between aquatic and terrestrial environments is less
rigid than that of many cartographers or civil engineers (see Sand-Jensen et
al. 1992). I shall define an aquatic habitat as one which has a permanent, or
temporally determinate but impermanent, occurrence of water over the
solid substratum. I thus include not only permanent water bodies, but also
their fringes subject to tidal or seasonal submersion of the substrata and thus
of any plants growing on them. I also (arbitrarily) consider mainly the plants
of such habitats whose photosynthetic organs are below the water surface
during periods of submersion. Another arbitrary exclusion is those terrestrial
poikilohydric plants which have a regular hydration period (e.g., desert
lichens supplied with dew at dawn each day: Lange et al. 1970).
15.3 The Diversity of Aquatic Plants
Primarily, aquatic plants (Fig. 15.1; d. the usage of Sand-Jensen et al.
1992) comprise essentially all aquatic Orevolvers at the prokaryotic level of
organization [cyanobacteria; chloroxybacteria (= prochlorophytes)] as well
J.A. Raven
15.1 Introduction
To address the topic of the ecophysiology of photosynthesis in aquatic plants
in the space allotted is a daunting task, and the coverage must of necessity
be very selective. Since this Volume is honoring Professor Dr. Lange, I shall
emphasize those aspects which interface with his work, and since the rest of
the Volume deals with terrestrial plants, I shall emphasize more generally
the comparison with terrestrial plants. My third objective is to address
particularly those aspects which most interest me and which are, or could
be, growth-points in research.
15.2 Definition of the Aquatic Habitat
Nature's distinction between aquatic and terrestrial environments is less
rigid than that of many cartographers or civil engineers (see Sand-Jensen et
al. 1992). I shall define an aquatic habitat as one which has a permanent, or
temporally determinate but impermanent, occurrence of water over the
solid substratum. I thus include not only permanent water bodies, but also
their fringes subject to tidal or seasonal submersion of the substrata and thus
of any plants growing on them. I also (arbitrarily) consider mainly the plants
of such habitats whose photosynthetic organs are below the water surface
during periods of submersion. Another arbitrary exclusion is those terrestrial
poikilohydric plants which have a regular hydration period (e.g., desert
lichens supplied with dew at dawn each day: Lange et al. 1970).
15.3 The Diversity of Aquatic Plants
Primarily, aquatic plants (Fig. 15.1; d. the usage of Sand-Jensen et al.
1992) comprise essentially all aquatic Orevolvers at the prokaryotic level of
organization [cyanobacteria; chloroxybacteria (= prochlorophytes)] as well