Effects Of Rare Earth Element Lanthanum On Soybean Population Modules

The rare earth elements?REEs?are widely used in industry,agriculture,military and other fields,leading to increasing environmental and ecological risks.Studies have shown that REEs have toxic effects on plant individuals.However,there have been no study on the effects of REEs on plant populations.Plants exist in the form of populations in the natural state.Under different population densities,the responses of plants to REEs will inevitably be different.Therefore,revealing the effect of REEs on plants at the population level can more objectively evaluate the toxic effects of REEs on plants and the influencing mechanisms.In view of this,the soybean?Glycine max?,a cash crop recommended by the U.S.Environmental Protection Agency for toxicological studies,was selected as the study object.A representative REE?La????was selected to simulate REE pollution.The effects of different concentrations of La???on growth status of soybean population modules?roots,stems,and leaves?at different densities were studied,and their impact mechanisms were explained from the perspectives of photosynthesis,chlorophyll fluorescence parameters,and content of La in each module.The main findings are as follows:?1?The toxic effects of La???on the growth of soybean population modules:at low population density?10 plants per pot?,compared with the control group?not treated with La????,after treatment with low,medium,and high concentrations of La???(0.08,0.40,and1.20 mmol·L^-1),the root tip number,root volume,main stem length,stem diameter,the leaf member,leaf area,dry weight of above-ground modules,and dry weight of underground modules of the soybean population were all present.The decrease amplitude increases with increasing La???concentration,and increases with the La???exposure time.At medium and high population densities?20,30,and 40 plants per pot?,compared with the control group,after the treatment of medium and high concentrations of La???,the growth indexes of above-mentioned modules of the soybean population showed a significant decline.The decrease amplitude increases with increasing La???concentration,and increases with the La???exposure time.The correlation analysis showed that the toxic effect of La???on the growth of each module of the soybean population was due to the accumulation of La in each module.?2?The first mechanism for La???affecting the growth of soybean population modules:change in photosynthesis of soybean population.At low population density,compared with the control group,after treatment with low,medium,and high concentrations of La???,the P_n?G_s?C_i?AQY and CE of the soybean population were all present.The decrease amplitude increases with increasing La???concentration,and increases with the La???exposure time.At medium and high population densities,compared with the control group,after the treatment of medium and high concentrations of La???,the above-mentioned photosynthetic indexes of the soybean population showed a significant decline.The decrease amplitude increases with increasing La???concentration,and increases with the La???exposure time.The correlation analysis showed that La???produced a toxic effect on the growth of population modules by increasing the La content in the soybean population modules and reducing the photosynthesis.?3?The second mechanism for La???affecting the growth of soybean population modules:change in chlorophyll fluorescence parameters of soybean population.At low population density,compared with the control group,after treatment with low,medium,and high concentrations of La???,the C_Chla?C_Chlb?F₀?F_m?QY_<sub>max?QY_<sub>Lss?ETR?F_v/F₀?qL_<sub>Lss?NPQ_<sub>Lssss of the soybean population were all present.The decrease amplitude increases with increasing La???concentration,and increases with the La???exposure time.At medium and high population densities,compared with the control group,after the treatment of medium and high concentrations of La???,the above-mentioned chlorophyll fluorescence parameters of the soybean population showed a significant decline.The decrease amplitude increases with increasing La???concentration,and increases with the La???exposure time.The correlation analysis showed that La???affected the chlorophyll fluorescence parameters by increasing the La content in the soybean population modules,thereby reducing the photosynthesis and producing toxic effects on the growth of the population modules.In summary,the following conclusions can be drawn:?1?La???showed a toxic effect on the growth of soybean populations,and the poisoning effect increases with the increase of La???concentration.?2?La???interfered with the chlorophyll fluorescence parameters and reduces photosynthesis of soybean population by increasing the La content in the soybean population,and thus has a toxic effect on the growth of population modules.?3?The effect of La???on the module growth,photosynthesis and chlorophyll fluorescence parameters of soybean population was as follows:10 plants/pot>20 plants/basin>30 plants/pot>40plants/pot,ie the increase of soybean population density could alleviate the toxic effects of La???on soybean populations to a certain extent.The above findings provide insights for a deep understanding of the mechanism of La???pollution on the impact of plant population modules and scientific evaluation of potential environmental ecological risks of La???pollution in agricultural soils.