Studies On The Photosynthetic Characterizations And Distributions Of Rear Earth Elements In Fern Dicranopteris Dichotoma

In order to elucidate the distributions of rare earth elements in fern (Dicranopteris dichotoma Bernh.) and the photosynthetic characterizations of Dicranopteris dichotoma, the concentrations and fine location of rare earth elements in Dicranopteris dichotoma in light, heavy rare earth elements mine and non mining area in Longnan county of Jiangxi province, China were investigated by means of inductively coupled plasma-mass spectrometry (ICP-MS), transmission electron microscopic (TEM), and energy-dispersive X-ray microanalysis (EDAX). The photosynthetic characterizations of Dicranopteris dichotoma in natural conditions and non rare earth elements hyperaccumulator Cucumber (Cucumis sativus Linn) treated with high concentrations LaCl3 also had been studied. Results showed that: 1. More excitation energy was distributed to PS II in cucumber after treated with 0.5 mmol·L-1 LaCl3. The inhibitory effects of 1 and 2 mmol·L-1 LaCl3 were mainly on the growth rate, oxygen evolution, and complete rate of chloroplast of cucumber seedling. This was due to the damage effects of LaCl3 on the cell structure and chloroplast membrane of cucumber, which resulted in the breakage of thylakoid membrane, the fall of PS II photosynthetic activities and retardation of growth of cucumber. 2. Fern Dicranopteris dichotoma was one of hyperaccumulator of rare earth elements. The distributions of rare earth elements in Dicranopteris dichotoma in light and heavy rare earth elements mine were lamina>root>soil>stem>petiole. The distributions of rare earth elements in Dicranopteris dichotoma in non mining area were lamina>root>stem>petiole. The fractionation of rare earth elements was occurred from stem to petiole in the transportation and accumulation of rare earth elements in Dicranopteris dichotoma. The heavy rare earth elements concentrations in stem, petiole, and lamina were low, while the light rare earth elements concentration in lamina was high. 3. Rare earth elements deposits can be found in the intact mesophyll cell and epidermal cell of Dicranopteris dichotoma. The rare earth elements concentration in the chloroplast of Dicranopteris dichotoma in non mining area was about 5% of total rare earth elements concentrations in lamina, while rare earth elements concentration in the chloroplast of Dicranopteris dichotoma was about 10% in light rare earth elements mine. A part of them were located in the chloroplast thylakoid grana lamella, which was embedded with PS II. 4. The hyperaccumulation of rare earth elements in Dicranopteris dichotoma was determined by both environment and its genetic characters, but mainly determined by its own physiological and biochemical characters. The mechanisms of hyperaccumulation of rare earth elements in Dicranopteris dichotoma were confining rare earth elements in cell wall, vacuole, and excretion combining materials to form rare earths elements deposits so that avoid of damages effects on photosynthetic characterizations. 5. Comparing to Dicranopteris dichotoma in non mining area, the electron transport rate of whole photosynthetic chain in chloroplast membrane increased 34.9%, the electron transport rate of PS II increased 252.9%, and the electron transport rate of PS I increased 16.8% in Dicranopteris dichotoma in light rare earth elements mine. The increase of the electron transport rate of whole photosynthetic chain was mainly resulted from the increase of the electron transport rate of PS II. This was concerned with distribution of more excitation energy to PS II, the increase of the content of chlorophyll protein complexes of PS II reaction centers (67.0%) and the content of light harvesting chlorophyll protein complexes of PS II in Dicranopteris dichotoma in light rare earth elements mine. 6. Comparing to Dicranopteris dichotoma in non mining area, the electron transport rate of whole photosynthetic chain in chloroplast membrane increased 46.3%, the electron transport rate of PS II increased 23.8%, and the electron transport rate of PS I increased 60.4% in Dicranopteris dichotoma in heavy rare earth elements mine. The increase of the electron transport rate of whole photosynthetic chain was mainly resulted from the increase of the electron transport rate of PS I. This was concerned with the increase of the content of protein complexes of PS I reactioncenters (60.0%) in Dicranopteris dichotoma in heavy rare earth elements mine. In conclusion, the active hyperaccumulation of rare earth elements in Dicranopteris dichotoma was mainly determined by its own physiological and biochemical characters. It can fix rare earth elements in cell in deposits form and change physiological metabolize to avoid the effects of high concentrations of rare earth elements on its photosynthetic characterizations. Dicranopteris dichotoma can be used as phytoremediation material in the pollution control engineering of rare earth elements pollution.