The Early Developmental Stages Of Laminaria Japonica Aresch In Response To The Interaction Of Enhanced UV-B Radiation And Other Environmental Factors

? For comprehensive understanding the effects of global enviromental changes, especially of increasing UV-B radiation, on the growth and development of macroalgae, the responses of the early developmental stages of Laminaria japonica Aresch to the interaction between enhanced UV-B radiation and other environmental factors were studied in the laboratory based on the integrated techniques and methods with experimental ecology, data statistics analysis and electronic microscopy.1. The response of the early developmental stages of L.japonica to enhanced UV-B radiationThe low UV-B radiations (11.7-23.4 J m-2 d-1) had no significant effects on zoospores attachment, but when the UV-B dose > 35.1 J m-2 d-1 the attachment decreased significantly compared with the control. Germination of embryospores was >93% under the low (11.7 - 35.1 J m-2 d-1) doses, and in the range of 78.5% - 88.5% under the high (46.8 - 70.2 J m-2 d-1) UV-B doses, indicating a significant radiation effect. Under the higher UV-B exposure (35.1 - 70.2 J m-2 d-1), all of the few gametophytes formed from embryospores died 120 h post-release. After exposure to the low UV-B radiation (11.7 - 23.4 J m-2 d-1), the formation of sporophytes decreased and the female gametophyte clones increased compared with the control. However, the sex ratio and the relative growth of female gametophytes/sporophytes had not significantly changed. According to the results, enhanced UV-B radiation has a significant effect on the early development of L. japonica under laboratory conditions, suggesting that the UV-B radiation could not be overlooked as one of the important environmental factors influencing the ontogeny of macroalgae living in marine ecosystems.2. The interaction between temperature and UV-B radiation on the early development of L.japonicaEmbryospore germination was stimulated by UV-B radiation (11.7,23.4 and 35.1 J m-2 d-1) at 5℃, and UV-B radiations had no significant effects on embryospore germination at 10,15 and 20℃. Gametophytes incidences were irrelevant to the doses of UV-B radiation at 15℃, however, the incidences of gametophytes significantly decreasing as UV-B doses increasing at the three other temperatures. Both the percentage male gametophytes and the fecundity of female gametophytes decreasing with UV-B radiation dose increasing at 20℃showed that the significant interaction existed between 20℃and UV-B radiation(0,11.7,23.4 and 35.1 J m-2 d-1). At 30th d, the incidences of sporophytes in all experimental groups at 10℃were obviously higher than that of the other combinations of the same UV-B doses and other temperatures respectively. However, the highest incidences of female gametophytes clones occured at 20℃.The results suggested that significant interactions existed between temperature and UV-B radiation, which significantly influenced the early development of L.japonica, such as the incidence and development of gametophytes, incidences of both sporophytes and female gametophytes clones.3. The interaction between temperature and UV-B radiation on gametophyte ultrastructuresThe main ultrastructural influences on gametophytes of L.japonica by the combinations of temperature and UV-B radiation were thickness of cell wall, chloroplast structures and the changes in number and morphology of pyrenoid. At both 5 and 10℃, UV-B radiation caused gametophyte cell wall thin significantly, however, cell wall became thicken obviouly at15℃. The lamellar structure of chloroplast was unclear and thylakoid appeared fracture or stick under the treatments ?of combinations of the above three temperatures and UV-B radiation. The number of pyrenoid seemed to be stimulated by UV-B radiation and more than two pyrenoids in gametophyte cells were detected. Meanwhile, the differences in the size of mitochondria, the number of lipid globuli and the morphology of abnormal cells were also discovered between the control groups and the combination groups of temperature and UV-B radiation. Considering the results of the previous chapter, we concluded that proper high temperature could reduce the damages on chloroplast, mitochondria and other organelles caused by the UV-B radation due to the thickness of cell wall increased at high temperature.4. The interaction of nutrient elements (nitrogen, phosphorus) and UV-B radiation on the growth and development of L.japonica in its early life historyOur data suggested that there were significant interactions between UV-B radiation and different nitrogen and phosphorus concentration, which significantly affected the embryospores germination, gametophytes formation, young sporophyte and female gametophyte clones incidence. The optimal conditions for gametophytes formation, young sporophyte incidence and female gametophyte colones incidence were the combination of N-0, P-0 and UVB-0, the combination of N-1, P-2 or P-1 and UVB-0, and the combination of N-0, P-1 and UVB-2 respectively. The main influence caused by UV-B radiation alone on the female gametophyte size and relative growth rate (RGR) was not significant, but the RGR was affected significantly by the two-dimensional interaction of nitrogen, phosphorus concentration and UV-B radiation (N * P, N * UVB, P * UVB). The proportion of male gametophytes was significantly affected by UV-B radiation, the two-dimensional (N * P, N * UVB, P * UVB) and the three-dimensional ( N * P * UVB) interactions, but the nitrogen or phosphorus concentrations had no significant effects. The results indicated that the interactions between UV-B radiation and nitrogen or phosphorus concentration in seawater may change the growth and development of L.japonica in its early life history. 5. The response of the early developmental stages of L.japonica to enhanced UV-B radiation under different PAR intensity and light quality conditionsVariance analysis showed that the adverse effects of UV-B radiation on the formation of gametophyte, female gametophyte development and chlorophyll content were smallest when PAR intensity was at 35μmol photons m-2 s-1, and the PAR intensity could promote the incidence of female gametophytes clones which would further restrain the incidence of young sporophytes. The interaction between light quality and UV-B radiation had significant impacts on the formation of the gametophytes, female gametophytes development, young sporophytes or female gametophyte clones happened and Chl-a content. Compared with white light, blue light could significantly alleviate the adverse effects of UV-B radiation on the incidences of gametophytes, female gametophytes development and Chl-a content. The adverse effects of UV-B radiation under red light on the incidences of gametophytes were less than white light, and green light was the most disadvantaged for the early development of L.japonica. Blue light could stimulate the incidence of female gametophytes clones and the optimum condition for clones happen was the combination of blue light and 23.4 J m-2 d-1 dose of UV-B in our experiments. The results suggested that the interaction of PAR intensity, light quality and UV-B radiation could significantly effect the formation of the gametophytes, female gametophytes development, young sporophytes or female gametophyte clones incidence and Chl-a content.6. The effect of UV-B radiation on the growth and physiological of the young sporophytes of L.japonicaDuring the period from the 2th d to 10th d post UV-B radiation, the length and weight relative growth rates of young sporophytes under three doses of UV-B radiation treatments(11.7 J m-2 d-1, 46.8 J m-2 d-1, 93.6 J m-2 d-1) were significantly lower than that of the control (0 J m-2 d-1); the changes of Chl-a content from the 6th to the 10th day under the UV-B doses 11.7 J m-2 d-1 and 93.6 J m-2 d-1 showed inverse, which indicated that low UV-B dose could provoke the increase of Chl-a content and high dose could inhibit; the ATPase activities of young sporophytes treated with the two doses 46.8 J m-2 d-1 and 93.6 J m-2 d-1 were significantly lower than that of the control, and no obviously differences detected between the low dose 11.7 J m-2 d-1 and the control. Under the conditions of the shortage of N/P element accompanying with the UV-B dose 46.8 J m-2 d-1, there were no significantly difference between the relative growth rate of young sporopytes and that of just under the UV-B dose 46.8 J m-2 d-1; During the early period of the experiment (from 2th d to 4th d), the ATPase activities treated with the shortage of N/P element and the UV-B dose 46.8 J m-2 d-1 simultaneously were obviously higher than that of treated with the UV-B dose 46.8 J m-2 d-1 only, however, inverse changes appeared at the late stage; the Chl-a content under the coation of the shortage of N/P and UV-B radiation was significantly lower than that of the UV-B dose 46.8 J m-2 d-1 only, which suggested that the shortage of N/P intensified the impact of UV-B radiation on Chl-a content. Our results also suggested that a certainly intensity of photosynthetically active radiation could relieve the influence of the high UV-B dose 93.6 J m-2 d-1 on the growth and physiology of the young sporophytes.