Experimental study on growth of Hydrilla verticillata under different concentrations of bicarbonate and its implication in karst aquatic ecosystem.

Bicarbonate (HCO3−) is one of the dominant carbon forms in the aquatic ecosystem and carbon cycle in karst areas. Recent studies have focused on the HCO3− utilization by aquatic plants to assess karst carbon sink at a watershed scale. However, the predominated researches inadequately address the effects on growth of submerged plants in various HCO3− conditions and how the submerged plants affect the karst carbon cycle. Here, H. verticillata was selected as a research object in different HCO3− concentrations. Plant morphology and water chemistry were analyzed to comparatively study the growth strategy and carbon utilization of submerged plants under various HCO3− conditions. The results show that the HCO3− aquatic environment can remarkably promote the growth of H. verticillata in terms of biomass, apical shoots, lateral shoots, and root production. The optimum concentration on biomass accumulation and lateral shoots growth is 4 mmol L−1; while, it is 8 mmol L−1 for the apical growth. But overall, the biomass accumulation is one order of magnitude higher than that in the control group. Despite the abundant dissolved inorganic carbon can significantly stimulate the growth of submerged plants, the respiration of H. verticillata suffers a certain inhabitation when the HCO3− concentration exceeds 4 mmol L−1. In karst aquatic environment, the existing HCO3− not only promotes the growth of submerged plants by means of supplying abundant dissolved inorganic carbon but also creates an alkaline water environment to buffer CO2 from the atmosphere. As a consequence, the presence of submerged plants has greatly enhanced the stability of karst carbon sink. [ABSTRACT FROM AUTHOR]