The Bioremoval Of Nitrogen, Phosphorus, Cadmium, Chromium,Copper And Nickel By Gracilaria And Its Physiological And Biochemical Responses

With high economical, medical and environmental protection benefits, Gracilaria is the type of strong adaptability and fast growth, high yield, simple cultivation method and promotion easily. Under the experimental ecology, this article mainly investigated the bioremoval of nitrogen, phosphorus and four heavy metals iron including cadmium, chromium, copper and nickel of Gracilaria lichenoides, as well as its physiological and biochemical responses on it. Meanwhile, the mechanism of physiological and biochemical response to Cu stress in Gracilaria lichenoides and Gracilaria lemaneiformis were also compared to provide theoretical basis and practical guidance for the Gracilaria as a bioremediation or bioindicator of the environment pollution. The results showed that:1. The uptake rates (SNUR and LNUR) and uptake efficiency (SNUE and LNUE) of N (TIN) and P (PO43--P) by Gracilaria lichenoides for short-term (0-4h) and long-term (over a24h period at14th day) were studied,showing that the optimal N:P ratio in culture media which SNUR and LNUR for N and P by G. lichenoides reached the highest value among different N/P concentrations (P<0.05) was16:1. The reached maximum SNUR of N and P by G. lichenoides was12.85and0.79μmol/(gDW·h), respectively, when the N/P concentration in medium was1200/75and960/60μmol/L; and the reached maximum LNUR of N and P by G. lichenoides were4.23and0.31μmol/(gDW·h), respectively, with the N/P concentration in medium of480/30μmol/L.2. On treatment with mixed nitrogen sources, the uptake rates of different state compounds of nitrogen for Gracilaria were compared, showing the uptake rates of NH4+-N of Gracilaria was significantly higher than NO3--N, especially for long-term absorption; light treatment had significant effects on the uptake of NH4+-N and NO3--N, especially for the NO3--N absorption. What’s more, the activities of NR and GS were induced by the NH4+-N and NO3--N respectively, which in turn promoted the uptake of this two states of nitrogen.3. During the nitrogen and phosphorus starvation, the growth dropped, the color of algae turned gradually from red to yellow/white,the pigment, proline, protein content as well as the antioxidant capability of G. lichenoides were all affected and weakened; meanwhile, the atrophy of chloroplast and mitochondrial、increase of the grain starch in cell also occurred; while under the condition of the N/P concentration in medium of1200/75and960/60μmol/L for5-7days, the antioxidative defense system of G. lichenoides was obviously inhibited,leading to the accumulation of great amount of harmful free radicals and lipid peroxidation products;some damaged ultrastructure changes occurred in the chloroplasts including the thylakiod swollen and lined irregularly, number increase;volume increase, and significant accumulation of starch grains in the chloroplasts.Besides,the growth rate declined,and the pigment, protein content decreased dramatically.4. On the condition of480/30-750/45μmol.L-1N/P, the SGR of Gracilaria lichenoides reached the highest value,and the photosynthetic pigments、physiological and biochemical、antioxidative defense system and the ultrastructure indexes all indicated that the best N/P concentration of short-term (<7d) and long-term (15d) for Gracilaria lichenoides were N/P750/45μmol.L and N/P480/30μmol.L-1respectively. While treatment with N/P concentration of480/30μmol.L-1,the Gracilaria lichenoides could achieve optimum status with the ratio of N:P and ρ(NH4+-N):ρ(NO3--N) of16:1-32:1,6:0-1:1, respectively.5. In this trial, whatever the single heavy metal mass concentration (0.05mg.L-1or0.5mg.L-1)condition or composite conditions with equal heavy metal concentration (0.5mg.L-1or1.0mg.L-1) condition, the removal efficiency, removal rate, and accumulation of four heavy metals extra-and intra-cellularly of Gracilaria were all shown with the following sequence: Cu>Ni>Cr>Cd.6. With increasing Cu, Ni, Cr, Cd concentrations, the accumulation of harmful reactive oxygen species(ROS) and lipid peroxidation products(MDA) increase gradually; SOD, CAT, POD, APX, GST, GR, and T-AOC activities of antioxidative defense system were all first activated and then inhibited, both the soluble protein and photosynthetic pigments were dropped; moreover the damage of the ultrastructure of cells clearly occurred in the chloroplasts (thylakoid of chloroplast swollen, evident plasmolysis phenomena, significant accumulation of starch grains, increase of osmiophilic granule number, bilayer membrane structure of the chloroplast was ruptured, disappearing of the nucleoli, acumination of deposits of Cu on the surface of the cell wall and the chloroplast envelope),the composition of the chloroplasts elements changed gradually. The analysis results indicated that the physiological tolerant threshold concentration of Cu, Ni, Cr, Cd was0.5,2.5,2.5,5mg.L-1respectively for Gracilaria.7. Both the relative higher and lower P concentrations (1.5μmol.L-1or60pmol.L-1) have adverse effects on the stress tolerance of Gracilaria to Cu, Ni, Cr, Cd, including the decline of the growth and the aggravation of the cells’ultrastructure injury. Whereas the tolerance of Cu、Ni、Cr、Cd stress increased under the appropriate concentration of15μmol.L-1P.8. In G. lemaneiformis, decrease in growth, pigment (chlorophyll a, chlorophyll b, phycobiliprotein, β-carotene) content and photosynthetic activity was more prominent, and the threshold concentration that caused a notable inhibition in SGR was50μgL-1Cu2+, making it a suitable candidate of potential bioindicator to Cu2+pollution.