|Other Abstract||The ecophysiology of an edible Cyanbacterium of Nostoc sphaeroides were studied in this research. In order to gain insight into the relationship between wild yield and environment factors such as climate, water, soil and human activity and so on, methods of physiology, ecology, wild investigatation and culture have been used in this research. The main results were the following:
The latest wild resource and distribution area of N. shpaeroides were investigated by using methods of general survey and sample survey, the results showed that current annual yield was less than 0.5 ton, the area of habitat was less than one fifth of its used to be. Distribution of N. shpaeroides depended on content of water and phosphorus in soil, which might be limiting factors for its distribution in wild conditions. Difference in field management and crop planted also resulted in different distribution of N. shpaeroides. However, nutrient content in water and organic substance in soil were not limiting factors for distribution of N. shpaeroides, which was considered as the limiting factors for its distribution in previous report. The decline of N. shpaeroides was slowed and methods to conserve the habitat of N. shpaeroides were processed in our investigation period, resulted from more attention paid from government and the high economic benefits. It is reasonable to assume that the wild yield of this species will increase in the following years.
After treated colonies of N. shpaeroides with simulated culture condition as it grew in the period of rice field, the coccoid cells were investigated after cultured at 30℃ in darkness for 60 days. After isolated coccoid cells were transferred to fresh BG110 medium, the cell growth and development were recovered and formed colonies later. The result indicated that coccoid cells might be the algal seeds for next season’s growth after 4 months long time disappeared.
In the present research, growth, photosynthetic activity, pigment content, and membrane permeability of Nostoc sphaeroides grown in different nitrogen resources including urea, ammonium, and nitrate and in N-free control were investigated to gain insight into the relationship between declined production of N. sphaeroides and application of nitrogen fertilizers in paddy fields. Results indicated that ammonium and urea were drastically toxic to N. sphaeroides, triggered a lot of colonies broke and lysed. Additionally, rapidly decrease in biomass was found in plots added ammonium, and seriously inhibition of growth was found in the application of urea and ammonium at all the three levels in experiment. Colonies grown in plots added ammonium was apt to form a distribution with proportion of larger size colonies increased, indicated a low growth rate. The steepest initial slope (α) and highest photosynthesis pigment content belonged to nitrate grown colonies and the highest photosynthetic efficiency (Fv/Fm) belonged to N-free and nitrate grown colonies. Both urea and ammonium had inhibitory effect on Fv/Fm, regardless of the concentrations used in experiment. Application of urea and ammonium resulted in pigment bleached and membrane damaged, leaded to decrease in pigment content and increase in membrane permeability. Our finding suggested that extensive and abusive application of urea and ammonium fertilizer might be an important factor limiting the productivity of N. sphaeroides.
The effects of butachlor on the physiological activity and cell metabolizable products of N. sphaeroides were focused in this study. After exposure to the different concentrations of butachlor, it was found that photosynthetic rate, respiration rate, and photosystem II activity improved when the concentration of butachlor below 5 mg•L-1, however, the reverse results were obtained when the concentration of butachlor was above 5 mg•L-1. Meanwhile, the structure and biological function of the N. sphaeroides were destructed under stress, the permeability of plasma membrane of N. sphaeroides increased as well as the contents of MDA and O2.-with the concentration of butachlor increasing. While the content of carotenoids increased and the activity of SOD improved to resist the damage of butachlor when N. sphaeroides was exposed to low concentration of butachlor. But for the actual using concentration, this resistance was quite limited, so it is necessary to limit the use of butachlor in order to protect the habitat of Ge-Xian-Mi.|