Submersed macrophyte growth at low pH: carbon source influences response to dissolved inorganic carbon enrichment

Abstract

Summary 1. Twenty‐one submersed macrophyte species were grown in the greenhouse at low and high dissolved inorganic carbon (DIC) concentrations and at pH 6 to test the hypothesis that growth response to DIC enrichment in the water column would be greatest for species able to use both bicarbonate (HCO ) and free CO 2 from the water column, intermediate for species restricted to free CO 2 in the water column, and least for those species able to use free CO 2 from both sediment porewater and the water column. 2. Relative growth rates (RGR) increased significantly with DIC enrichment for 12 of the 21 species. Bicarbonate users as a group averaged a 4.6‐fold increase in RGR with DIC enrichment, significantly greater than the 2.5‐ and 1.7‐fold increases of the water column CO 2 users and sediment CO 2 users, respectively. 3. The ability to use HCO , as measured by a pH drift technique, was positively correlated with the ratio of RGR at high DIC to RGR at low DIC for the 21 species. 4. Bicarbonate users also exhibited significantly lower belowground : total biomass (R : T) ratios than the other two groups, and alone showed a significant increase in R : T ratio with DIC enrichment. 5. Our results indicate that DIC availability may influence community structure in acidic and circumneutral lakes.