Alternate Title

Response of Turtlegrass to Natural and Reduced Light Regimes Under Conditions of Rhizome Isolation


To evaluate if rhizome integrity influenced the response of turtlegrass (Thalassia testudinum) shoots to experimental light reduction, we performed a field experiment in Perdido Bay, FL, from May to Oct. 2001. We used a factorial design, with light, rhizome integrity, and time as main factors. Light was reduced to about 40% with respect to ambient irradiance by means of a polyethylene mesh, and rhizomes along the external border of the 0.5-m2 experimental plots were severed with a knife at the beginning and middle of the experiment. Severing surrounding rhizomes had a significant (P < .05) negative effect on net aboveground primary production (NAPP), but this was only apparent from June to July, and there were no significant severing effects on aboveground biomass. Shading showed negative effects through time on aboveground biomass and NAPP, although the differences were not significant. Time was significant for belowground biomass, NAPP, shoot density, and leaf length and width and there were significant time-by-shading interactions for NAPP, aboveground biomass, and density. We conclude that the results of turtlegrass shading studies done over several months during the peak of the growing season are not influenced to any large extent by whether rhizomes are intact or not, indicating that previous studies of the effects of shading on turtlegrass can be compared without bias.