Comparison of methods for measuring production by the submersed macrophyte, Potamogeton perfoliatus L.1,2

Six conventional methods for measuring primary production of submersed vascular plants were compared to test for previously suggested inherent shortcomings in the O2‐exchange techniques. Production was measured for experimental populations of Potamogeton perfoliatus L., from upper Chesapeake Bay in five comparative studies, each including an O2‐exchange method. All techniques tested (14C incorporation and O2 evolution for both bottle incubations and undisturbed populations; biomass accumulation and inorganic carbon consumption for intact populations) compared favorably, with mean (molar) ratios of oxygen to carbon production ranging from 0.9 to 1.6. In addition, direct measurements indicated that rhizosphere release of O2 would introduce only small errors (<5%) in O2 production estimates. Although changes in lacunal storage of O2 can result in brief (5–25 min) delays between O2 production and evolution to the external water, simple methodological precautions can overcome such problems. We conclude that all available methods for measuring productivity of this and related species are potentially useful, each having its particular strengths and weaknesses, and the use of more than one method is recommended.