Fragment growth of rooted and rootless submerged aquatic macrophytes: effects of burial modes and decapitation of shoot apex

Some aquatic plant species are fragmented by mechanical forces in their environment. Since these fragments can take root in the sediment and establish new populations, they are important for the establishment success of some aquatic macrophytes. We hypothesized that burial and decapitation of shoot apical meristems would restrict the upward growth of buried fragments. We compared a rooted species (Myriophyllum spicatum L.) with a rootless species (Ceratophyllum demersum L.) in terms of growth of apical and decapitated allofragments buried in sediment in four different modes: buried completely, upper-half buried, lower-half buried, and unburied (floating in the water column). In M. spicatum burial or decapitation of the apex restricted the upward growth of fragments. The greatest growth of apical fragments was in the lower-half buried treatment and the least growth in the upper-half buried treatment. However, completely buried apical fragments did not show decreased growth compared with those in the lower-half buried treatment. All fragments of C. demersum showed vigorous growth (many branches and nodes and high values for biomass and relative growth rate) regardless of the fragment type or burial mode. Our results suggest that the effects of sediment burial are negligible for early regrowth of C. demersum after disturbance by high water flow. However, the pattern of burial in the sediment may adversely affect early regrowth of M. spicatum, especially for fragments without apical tips.

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