Physiology and biochemistry of pteridophytes

SynopsisThe biochemical characteristics of pteridophytes firmly ally them with other Tracheophyta, with Bryophyta and with the class Charophyceae of the algal division Chlorophyta. Pteridophyte sporophytes, like the sporophytes of other terrestrial Tracheophyta, generally have the attributes of homoiohydric plants. All gametophytes are poikilohydric. Many gametophytes, and some sporophytes, are desiccation tolerant.Quantitative comparisons between pteridophyte sporophytes and the sporophytes of other tracheophytes show that there are probably no systematic differences between the efficiency of important processes: examples are the quantum yield of photosynthesis, and the water use efficiency of organic matter accumulation, in the (mainly) C3 pteridophytes relative to other C3 tracheophytes. By contrast, the potential rales of physiological processes, as indicated by the conductance of photosynthetic (C3) carbon assimilation, and of water movement in the xylem, are generally towards the low end of the range for terrestrial tracheophytes. These low conductances restrict the maximum specific growth rate of pteridophyte sporophytes to rates lower than those found in annual angiosperms. Constraints imposed by the pteridophyte life cycle may have limited the capacity of pteridophytes to function in nature as annuals, and thus have reduced the selection pressure for high conductances (e.g. by a more widespread occurrence of vesseles in xylem of pteridophytes).