| 其他摘要 | Microalgal bio geochemistry of trace metals gives emphasis on the interaction between microalgae and trace metals for understanding effect of microalgae on distributing, migrating and accumulating of trace metals, also for understanding the changing of microalgal chemical component, structure, shape, function in different geochemical background. The changing of geochemical environment and thereby evocable ecological environment effect is one of the scientific focuses at present studied. Since industrial revolution, the human activity has strongly changed the content of trace metals in the part or whole earth surface layer. This forms potential threat to organism and human-itself. Phytoplankton plays an important role in aquatic ecological system. Phytoplankton drives biogeochemical cycle of some elements such as C, N, Si, P, 0, S and Fe by photosynthesis, bioaccumulation, biomineralization. Microalgae are sensitive to environmental change and so good response to the changing of trace metals geochemical behavior. So far, there are lots of researches on trace metals geochemistry and ecology of phytoplankton in lakes; however, there are few systematical researches on the interaction between phytoplankton and trace metals and it is also lack of experimental foundation to explain complex biogeochemical behavior of trace metals. The author of this dissertation has studied space-time distribution of trace metals and microalgae in plateau lakes that are Aha Lake, Baihua Lake and Hongfeng Lake; has studied bio-absorption/adsorption of Chlamydomonas reinhardtii and Chlorella pyrenoidosa on trace metals; has studied effect of trace metals on microalgal growth rate and external carbonic anhydrase; discusses the interaction between microalgae and trace metals on these studies. These studies help to explain some of complex biogeochemical behaviors of trace metals in lakes. The main conclusions are listed as followings: There are two maximums for the biomasses of microalgae in Aha Lake, Baihua Lake and Hongfeng Lake in 2002. One appear s in Spring and the other is in Autumn. This phenomenon resulted from co-action of multi-factors such as temperature, light, nutrition supply and preyed by zooplankton. The main microalgae in Baihua Lake and Hongfeng.Lakeare Cyanophyta and Chlorophyta and that are the same for Aha Lake in Spring; whereas Bacillariophyta is the main microalgae in Aha Lake in Autumn. The content of Chk in Aha Lake and Hongfeng Lake decreased with the increase of depth of lake water. The status of variation for every trace metal (Cu, Ni, Co, Zn and Mo) monthly is different Precipitation and microalgae both affect these variations. Acid 1 rain (precipitation) erodes carbonate rock located around lake drainage area and trace metals dissolved are input to lakes (e.g. Cu in the three lakes and Mo in Aha Lake). The trace element (Co, Cu Zn and Mo) has positive correlation with the biomasses of Cyanophyta and Chlorophytain Baihua Lake and Hongfeng Lake, respectively; these trace metals have some degree limiting the growths of these microalgae. Bacillariophyta in Aha Lake has negative correlation with every trace metal; this may result from the bioaccumulation by Bacillariophyta on these trace .metals. Phytoplankton absorbs, adsorbs and accumulates dissolved trace metals and so affect distributions of these dissolved trace metals in the depth of lake water; Other relative factors include microbe in the bottom of lake and current of lake water, etc. Equilibrium time of bio-adsorption by microalgae on trace metals (Mn, Fe, Co, Ni, Cu, Zn and Cd) depends on the way of how to treat with microalgae. The status of bio-adsorption by Chlamydomonas reirihardtii on each trace metal, in single ions system is different from the same trace metal in multi-ions system; this is because of competition among the trace metals in multi-ions system. In multi-ions system, the order of adsorption ability of dead algal cells on Cd, Zn, Cu, Co and Mn is consistent with the order of atomic weights of these trace metals; this indicates that dead algal cells are prior to choose trace metal with heavier atomic weight in the process of competition among these trace metals; In multi-ions system, the order of adsorption ability of live algal cells on Cd, Fe, Co andZn (Ni) is reverse to.the order of ion density of these trace metals; this indicates that live algal cells are prior to choose trace metal with lighter ion density in the process of competition.among these trace metals and is possible because of bio-fegulation by live algal cell. In single and multi-ions systems, as for live and dead, algal cells, the adsorption quantities on trace metals (Mn, Fe, Co, Ni, Cu, Zn and Cd) by Chlorella pyrenoidosa are larger or equal to that by Chlamydomonas reinhardtii and the adsorption quantities increase with the increase of the concentrations of trace metals. In single ions system, absorbing rate generally increases firstly with the increase of the concentration of trace metal and decreases since it gets the maximum; the.status of C. pyrenoidosa is similar to that of C, reinhardtii. The concentration of trace metal corresponding to the maximum absorbing rate is different from each other. The absorbing rates of Mn, Fe, Co, Cu and Zn by C. pyrenoidosa and C, reinhardtii are higher than that of Ni and Cd. The requirement and-endurance for trace metal by microalgae is different due to the different algal and trace metal species, respectively. In single ion system, as for C, pyrenoidosa and C. reinhardtii, the saturation of absorption on each trace metal gets more quickly than that of adsorption. Effects by trace metals (Mn, Fe, Co, Ni, Cu, Zn and Cd) on the. growths of C. pyrenoidosa and C, reinhardtii are relative to species of trace metals and microalgae, respectively, Ni, Cu, Zn and Cd have heavier effect than Mn, Fe and Co; it is heavier effects for C. reinhardtii than for C. pyrenoidosa. Growth rates of two microalgae generally increase firstly with the increase of the concentration of trace metal and decrease since it gets the maximum; this is like to the status of absorbing rate. This indicates the growths of two microalgae are relative to the quantities of trace metals in algal cells by absorbing. The bio-regulation of algal ceil also plays an important role in these processes. The activities of external carbonic anhydrase (CAe) of rnicroalgae.from Ah
Lake and Hongfeng lake are obviously higher than that of Chlamydomonas reinhardtii; This is because the activity of CAe is relative to ambient concentration of HCO3". The inhibition effects by Cd, Zn, Cu and Pb on CAe are species-species; for microalgae, it is also species-species. Effect of heavy metals on CAe appears to be threefold: (i) competing with CAe cofactor-Zinc; (ii) indirectly affecting the metabolism of CAe in algal cell; and (iii) directly changing bioactivity of CAe (e.g. Pb). Fe, Mn, Co, Ni and Cd in low concentration activate the activity of CAe of Chlamydomonas reinhardtii and inhibit in high concentration. The inhibitory effects by Cu and Zn on the activity of CAe of C. reinhardtii are heavier than that by Fe, Mn, Co, Ni and Cd. As for the action of bio-regulation of C, reinhardtii on effect by trace metals on CAe, it is most obviously for Fe and Mn, then for Co and Ni. 7. Microalgae are important factors that have influences on behaviors of trace metals in plateau lakes and the statuses of these influences depend on the species of microalgae. Microalgae can intensively change the contents of ambient trace metals and the changes of trace metals affect physiological and biochemical functions of microalgae. The interaction between microalgae and trace metals depends on the species of microalgae and trace metals and this species-difference is one of primary reasons that result complexity of the behavior of trace metal. |
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