Responses Of Variable Fluorescence Of Photosynthetic System Ⅱ In Prorocentrum Donghaiense Lu:Changes Of Nutrients

Prorocentrum donghaiense Lu is a common causative species which lead to large-scale algal bloom in the East China Sea. At present, numerous works, which focused on the influences of environmental factors, such as temperature, salinity and irradiance, on the growth of this species and the capability of the species to utilize nutrients, have been widely carried out. These studies provided sufficient theoretical supports for explaining the algal bloom. Photosynthesis is essential to the survival of plant; however, little is known about the relationships between photosynthesis and the growth and nutrient utilization of P. donghaiense.The variable fluorescence of photosynthetic system Ⅱ is an effective tool to indicate the photosynthetic capability. Here, the present study employed Phyto-PAM to determine the relationships between chlorophyll parameters and the growth, external nutrient concentrations and uptake rates of P. donghaiense. Besides, the study compared the different results of the evaluation of nutrient limitation between chlorophyll a concentration and variable fluorescence parameters, and further determined the nutrient-induced fluorescence transient. Finally, the regulation of non-photochemical quenching (NPQ) of P. donghaiense was studied under the Phosphorus (P)-limited conditions. The aim of the present study is to explore the indicating capability of fluorescence parameter for nutrient status of P. donghaiense, and to provide theoretical basic for further study. The results are as follows:1. Two kinds of population growth of P. donghaiense were developed by mean of controlling the external nutrient concentration:a. when the concentration was sufficient, the growth curve of P. donghaiense had obvious lag and exponential phase. Fv/Fm, OPSII and the ratio of active chlorophyll steadily increased in the lag phase and kept basically constant during the exponential phase; b. when the nutrient concentration is limited, the growth curve did not have clear exponential phase although the lag phase was still obvious. Three parameters unregularly fluctuated. The results showed that the chlorophyll parameter can indicate the growth of P. donghaiense in the presence of clear lag and exponential phase.2. Under batch cultural conditions, the chlorophyll parameters of P. donghaiense were significantly affected by the combining effects of population growth and external nutrient concentration. Fv/Fm, ΦPSII, the ratio of active chlorophyll, NPQ, alpha, rETRmax and IK was markedly linear to the nitrate concentration in cultural medium. The Fv/Fm,ΦPSII and NPQ entered to the multiple linear regression equation, and totally explained the variation of 74% of nitrate concentration. As to the external phosphate concentration, few significantly linear relationships were found. The uptake rates of nitrate and phosphate can be explained by the multiple linear regression equation, but only explained less than the variation of 65%.3. To avoid the influence of growth on the chlorophyll parameters, semi-continuous and continuous culture was employed to get the balanced growth of P. donghaiense. The results showed that the external nutrient concentration showed no significant impact on the chlorophyll parameters when P. donghaiense grew with different growth rates under balanced conditions. In this circumstance, irradiance and the concentration of carbon dioxide might affect the photosynthesis of P. donghaiense.4. The discrepancy between chlorophyll a concentration and variable fluorescence parameters was found when determining the nutrient status of P. donghaiense. The results of chlorophyll a concentration showed that the P. donghaiense with low growth rate was co-limited by nitrogen and phosphorus, whereas the results of variable fluorescence parameters showed that the P. donghaiense with low growth rate was P-limited. To avoid the influence of growth on the fluorescence signal, a method of nutrient-induced fluorescence transient was employed, the results showed that when the culture medium were P-deficient, the addition of phosphorus would induce the decrease of Ft; when the culture medium were N-deficient, the addition of phosphorus would not lead to the drop of Ft.5. P. donghaiense has the ability to protect themselves from the injury of high light exposure by up-regulating NPQ under P-limited conditions. Xanthophyll cycle and proton gradient play important roles. For P. donghaiense, the activation of xanthophyll cycle needed proton gradient, whereas NPQ was not induced when there was only proton gradient. When both the xanthophyl) cycle and proton gradient were inhibited, P. donghaiense might take other measures to induce NPQ.