# Effects of Climate Change on 2-Methyllisoborneol Production in Two Cyanobacterial Species
## 4 Discussion  
None of the three DIC treatments yielded significant differences in 2-MIB-producing potential. At 35 \({}^{\circ}\)C, the increase in DIC causes the carbon cycle in the water to generate more algal cells because more carbon would be available for photosynthesis and growth. Figure 3d,f suggest that a high DIC concentration promotes algal growth and leads to increased 2-MIB production. This means that when high temperatures and high DIC concentrations occur simultaneously (heat wave scenario), 2-MIB production by _Planktofl trix_ sp. increases quickly. A previous study found that DIC had a similar effect on _Chlamydomonas_[34]. In their study, the authors found that the photosynthesis of _Chlamydomonas moewusii_ was promoted in a saturated amount of DIC. For the insignificant differences in total 2-MIB and Chla concentration values under the three DIC treatments at 27 \({}^{\circ}\)C, it may due to the suppression by nutrient limitation. At 35 \({}^{\circ}\)C, the response may become more obvious. In the study of [PERSON] et al. [35], it was found that the response of cyanobacterial growth to rising CO\({}_{2}\) concentrations and elevated temperatures can be suppressed by nutrient limitation. When heat wave occurs, measures to prevent algal blooming should be taken. The results shown in Figure 4a are consistent with those of [PERSON] [23], who reported that the growth rate of _Pseudanabena_ sp. varied between 10 \({}^{\circ}\)C and 35 \({}^{\circ}\)C. In this study, _Planktofl trix_ sp. growth was not inhibited at 35 \({}^{\circ}\)C. The results shown in Figure 4a,b suggest that higher temperatures will shorten the lifecycles of _Dolichosperm spiroides_ and _Planktofl trix_ sp. and will the advance the onset of the logarithmic phase in laboratory-scale culture studies. The 2-MIB-producing potential in _Dolichosperm spiroides_ was higher at 35 \({}^{\circ}\)C than at 27 \({}^{\circ}\)C. The combined Chla data shows that after the 22 nd day, many of the cells began to die and disintegrate, which released 2-MIB and caused a large increase in extracellular 2-MIB. In contrast, temperature had no significant effect on the _Planktofl trix_ sp. 2-MIB-producing potential. Figure 6: Fitting curves of each DOM’s FI and 2-MIB concentration of _Dolichospermum spiroides_. (**a**) Extracellular DOM and 2-MIB at 27 \({}^{\circ}\)C; (**b**) Intracellular DOM and 2-MIB at 27 \({}^{\circ}\)C; (**c**) Extracellular DOM and 2-MIB at 35 \({}^{\circ}\)C; (**d**) Intracellular DOM and 2-MIB at 35 \({}^{\circ}\)C.  
Figure 4e,f show that the higher temperature will increase 2-MIB concentrations in water bodies where _Dolichospermum spiroides_ is dominant and that 2-MIB is synthesized in cells. Most of the 2-MIB remains in the cell until the cells die and break down. Then, the 2-MIB is released into the water. In contrast, _Planktothrix_ sp. transport 2-MIB to the extracellular area after the 2-MIB is synthesized. Therefore, extracellular 2-MIB concentrations were always higher in _Planktothrix_ sp. cultures compared to _Dolichospermum spiroides_ cultures. The results shown in Figure 4c,f also indicate that the contribution made by extracellular 2-MIB to the MIB/Chla ratio over time was more substantial than that made by intracellular 2-MIB. The EEM results suggested that humic acid was not the main component of the _Dolichospermum spiroides_ intracellular fluid. Extracellular concentrations of soluble microbial metabolites and fulvic acid increased significantly, whereas the humic acid concentration increased relatively slowly over time. At 35 \({}^{\circ}\)C, the concentrations of intracellular soluble microbial metabolites as well as tyrosine and tryptophan aromatic proteins were lower, while the concentration of extracellular fulvic acid, humic acid, and soluble microbial metabolites were higher than those at 27 \({}^{\circ}\)C. This result also suggests that a number of _Dolichospermum spiroides_ cells died at 35 \({}^{\circ}\)C and released their humus into the water.