Studies On The Effects Of Elevated CO₂ And UV-B On The Growth And Photosynthesis Of Nostoc Commune

Nitrogen fixing cyanobacteria are the major primary producer in some terrestrial ecosystems, which are in extreme environment or lack of nitrogen nutrition. The productivity and nitrogenase activity of nitrogen fixing cyanobacteria, which may be changed in the future environment, will affect these ecosystems significantly. Enhanced CO2 and UV-B will have to coexist for a very long period of time and their effects on the terrestrial nitrogen fixing cyanobacteria are receiving more concerns. In order to understand these effects, the changes of the growth, photosynthetic physiology and biochemical composition of Nostotc commune under different levels of CO2 and UV-B radiation were investigated in this study. In additionally, the filtration of UV-A and UV-C from UV-B light source were also carried out. The main results are as follows:(1) The concentration and pH of the potassium chromate solution could affect it's UV absorption properties. Potassium chromate solution, at the concentration of 0.4 mM and pH8, could remove both UV-A and UV-C radiations from UV-B light source effectively and result high penetration of UV-B radiation. It is very economic and convenient to use the manmade quartz vessel(35X1X20 cm) contained potassium chromate solution to study the direct bioeffect of UV-B radiation.(2) High level UV-B radiation (20 KJ m-2 d-1) inhibited the growth of N. commune significantly under 350 and 1500μL L-1CO2. But Low level UV-B (9 KJ m-2 d-1) radiation did not. Higher concentration of CO2 stimulated the growth of N. commune at the same UV-B radiation level. And the stimulation of the growth increased with the increasing UV-B radiation levels. The growth of N. commune under high UV-B and CO2 was faster than the that under 350μL L-1CO2 without additional UV-B radiation, which means that the biomass of N. commune might not decrease due to the increase of UV-B radiation in the future because of the increase of CO2.The trend of the changes of the content of chlorophyll in N. commune cells (per unit dry weight) were same as that for the growth of N. commune. High level UV-B destroyed the synthesis of chlorophyll while higher concentration of CO2 stimulated the synthesis of chlorophyll. UV-B radiation induced the synthesis of MAAs (triphenyl imidazole amino acid) in N. commune cells. And the content of MAAs on the basis of dry weight increased significantly with the increasing levels of UV-B and the time exposure to UV-B radiation. Under high level UV-B radiation, higher concentration of CO2 stimulated the synthesis of MAAs significantly but it was not under low level UV-B radiation.(3) Fv/Fm of N. commune decreased significantly with the increasing levels of UV-B radiation. And the inhibition of Fv/Fm ceased gradually with the increase of the radiation time. Higher concentration of CO2 could significantly increase the Fv/Fm of N. commune. In the early cultural stage, high level UV-B radiation inhibited the maximum photosynthetic rate, photosynthetic efficiency, dark respiration rate, inorganic carbon saturated maximum photosynthetic rate, but increased light saturation point and light compensation point. And higher concentration of CO2 contributed to the maximum photosynthetic rate, photosynthetic efficiency and respiration rate, but decreased light saturation point and light compensation point.(4) CO2 rise and UV-B enhanced infect the photosynthesis-related genes expression of nostoc, to fungus in six of gene expression under different treatments as time changes. Treated six groups of genes in cultured ntca second, fourth, eight days compared to the first day significantly reduced, especially in developing CO2 enrichment on the eighth day, whether or not to fungus in the 9 KJ m-2 d-1UV-B radiation and 20 KJ m-2 d-1UV-B radiation in ntca gene expression to be significantly higher than those without UV-B radiation nostoc's ntca gene expression, ntca gene in each treatment group differences in the expression of the eighth day, the rbcL genes and the psb similar differences have also emerged, psb and rbcL gene expression changes as time changes, the overall similar to ntca genes.In a word, CO2 and UV-B from the growth, physiology, gene expression infect Nostoc commune.