Study on the Ammonia Tolerance Threshold of Ottelia acuminata (Gagnep.) Dandy Seedling

As a typical representative plant of Erhai Lake in Yunnan Province, Ottelia acuminata (Gagnep.) Dandy has an important ecological status. Erhai Lakeside has characteristics of a low-polluted water that contains major polluted sources, such as ammonia. A simulated experi-ment based on these characteristics was per-formed in 2013 to determine the ammonia toler-ance threshold of macrophyte seedlings through the analysis of antioxidase system indices and malondialdehyde. The tolerance threshold of the seedlings was given as the symbol N_mtor. The re-sults showed that in a blank substrate simulated experiment, the ammonia tolerance threshold of the seedling is 0.5<N_mtor≤4.0 mg l⁻¹, which is al-most the same as that of Hydrilla varticillata (an anti-pollution macrophyte). The seedling can en-dure ammonia pollution, which means the spe-cies is not an "absolute clear-water macrophyte" and its cause of extinction is comprehensive. In the blank substrate, ammonia tolerance thresh-olds of stems, leaves, and roots of the seedlings are 0.5<N_mtor≤4.0 mg l⁻¹ and 0.5≤N_mtor≤4.0 mg l⁻\ respectively. The stems, leaves, and roots of Ottelia acuminata (Gagnep.)Dandy seedlings have almost the same ammonia tolerance thresholds.