Experimental study on growth ofHydrilla verticillataunder different concentrations of bicarbonate and its implication in karst aquatic ecosystem

摘要

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 HCO(3)(-)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 HCO(3)(-)conditions and how the submerged plants affect the karst carbon cycle. Here,H. verticillatawas selected as a research object in different HCO(3)(-)concentrations. Plant morphology and water chemistry were analyzed to comparatively study the growth strategy and carbon utilization of submerged plants under various HCO(3)(-)conditions. The results show that the HCO(3)(-)aquatic environment can remarkably promote the growth ofH. verticillatain 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 ofH. verticillatasuffers a certain inhabitation when the HCO(3)(-)concentration exceeds 4 mmol L-1. In karst aquatic environment, the existing HCO(3)(-)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 CO(2)from the atmosphere. As a consequence, the presence of submerged plants has greatly enhanced the stability of karst carbon sink.