Primary productivity inHalodule wrightii: A comparison of techniques based on daily carbon budgets

Bimonthly variations in shoot density, biomass, and blade productivity were used to estimate diel rates of primary productivity in conjunction with in situ measurements of photosynthesis and irradiance for a monospecific meadow ofHalodule wrightii Ascherson in Laguna Madre, Texas. Four separate techniques for estimating areal primary productivity were compared to estimates of primary production calculated from in situ measurements of photosynthesis and continuous recording of underwater light using the H_sat model. The clip and reharvest method, which is commonly used to measure shoot production, provided estimates ranging from 0.003 mol C m^?2 d^?1 in winter to 0.054 mol C m^?2 d^?1 in summer. In contrast, a method using aboveground biomass values, previously determined turnover rates, and belowground: aboveground biomass ratios provided estimates of primary production ranging from 0.04 mol C m^?2 d^?1 (winter) to 0.49 mol C m^?2 d^?1 (spring), similar to values determined from the H_sat model using in situ measurements of photosynthesis and ambient light regimes. Our results indicate that the clip and reharvest method dramatically underestimates primary productivity forH. wrightii, and that the inclusion of belowground biomass in carbon budget calculations is essential to obtaining realistic estimates of plant productivity. *** DIRECT SUPPORT *** A01BY069 00022