Effects Of Rare Earth Element Lanthanum On The Reproduction Rate Of Soybean Population

Rare earth elements?REEs?are widely used in industrial,agricultural and emerging industries,leading to an increase in the accumulation of REEs in the environment,which has become an environmental problem that cannot be ignored.Previous studies on the plant evaluation of the risk of exposure to REEs are rich,but they are mostly discussed at the individual level.The population as the basic unit of species in nature,from the population level is more in line with objective reality.Studies have shown that the damage of REEs to soybean plant varies with population density.However,the population characteristics are complex,and the indication effects of various parameters on the environment are not the same.The reproduction rate is one of the key factors affects the resource utilization,competition and survival of the population,which is also restricting population dynamics.Therefore,if the population reproduction rate can be used to evaluate the environmental safety of REEs exposure,it may have certain practical significance.In view of this,this study uses the experimental design of REEs exposure in the simulated environment to explore the effects of rare earth environmental pollution from the plant population level.The soybean?Glycine max?population recommended by the US Environmental Protection Agency for toxicology research is used as experimental material.A rare earth lanthanum[La???],which is ubiquitously present,simulated rare earth pollution was selected,and combined with the characterization of the population reproduction rate.The effects of La???on reproduction rate of soybean population were studied from the perspectives of different growth stages such as seedling stage,flowering and podding stage,seed-filling stage.The mechanism of effects of the reproductive rate of different density of soybean populations were revealed from the perspectives of the modules growth state and respiration of the population.The main findings are as follows:?1?The effects of La???on the reproduction rate of soybean population.The low concentration(0.08 mmol·L^-1)of La???treatment reduced the pod number,grain number,100-grain weight and reproduction rate of low-density(10 plant·pot^-1)soybean population at seedling stage,but promoted at the medium and high density(20,30 and 40 plant·pot^-1).The medium and high concentration(0.40 and 1.20 mmol·L^-1)of La???treatment showed inhibition on the above indicators for the soybean population at the seedling stage.For soybean population at the flowering and podding stage and seed-filling stage,the low concentration of La???treatment promoted the above indicators,while the medium and high concentrations of La???showed inhibition,and the degree of inhibition increased with the increase of La???concentration.Synchronous observations showed that the effects of La???on the above indicators of soybean population increased with the increase of treatment time,and decreased with the increase of population density.The effects of La???on the above indicators of soybean populations at different growth stages were generally presented:seedling stage>flowering and podding stage>seed-filling stage.?2?Revealing the influence mechanism of La???on the reproduction rate of soybean population from the perspective of population modules growth.Low concentration of La???treatment reduced leaf area,stem length,root length,root volume,root surface area,dry weight of the aboveground and dry weight of the underground of the low-density soybean population at seedling stage,while promoting at medium and high density;Under the medium and high concentration of La???treatment,the above indicators of soybean population at the seedling stage were inhibited.For the soybean population at flowering and podding stage and the seed-filling stage,the low concentration of La???treatment promoted the above indicators,while the medium and high concentrations of La???showed inhibition,and the degree of inhibition increased with the increase of La???concentration.Synchronous observations showed that the effects of La???on the above indicators of soybean population increased with the increase of treatment time,and decreased with the increase of population density.Correlation analysis showed that at the seedling stage,reproduction rate indices were mainly correlated with the root modules indices,indicating that the seedling stage mainly affected the reproduction rate by affecting the root nutrient absorption and the supply of respiratory energy;At the flowering and podding stage and seed-filling stage,the soybean population reproduction rate indices and the modules indices are correlated,which indicates that the flowering and podding stage is a strong growth period,and the member growth is required to supply the organic matter and energy;while the seed-filling stage mainly forms the grain formation and development,which is also the reason why the seed-filling stage is more correlated with the 100-grain weight than the flowering and podding stage.The effects of La???on the above indicators of soybean populations at different growth stages were generally presented:seedling stage>flowering and podding stage>seed-filling stage.Principal component analysis can also prove the above assertion.?3?Revealing the influence mechanism of La???on the modules growth of soybean population from the perspective of population respiration.Low concentration of La???treatment reduced photorespiration rate?P_r?,dark respiration rate?R_d?,key enzymes activity in photorespiration?GO,GS,CAT?,and key enzymes activity in dark respiration?HK,PK,ICDH,COX?of low density soybean populations at seedling stage.However,it has a promoting effect on medium and high density;the medium and high concentration of La???treatments have inhibitory effects on the above-mentioned indexes of soybean population at seedling stage.For soybean population at the flowering and podding stage and the seed-filling stage,the low concentration of La???treatment promoted the above indicators,while the medium and high concentrations of La???showed inhibition,and the degree of inhibition increased with the increase of La???concentration.Synchronous observations showed that the effects of La???on the above indicators of soybean population increased with the increase of La???treatment time,and decreased with the increase of population density.Correlation analysis showed that the respiration of soybean population was mainly correlated with the growth of aboveground modules during seedling satge,which indicated that the seedling stage mainly affected the accumulation of photosynthesis organic matter and the utilization efficiency of stem length to light resources and space;At the flowering and podding stage and seed-filling stage,the respiration and modules growth of the soybean population were correlated,which was related to the vigorous development period,supplying organic matter and energy to meet the growth of the moduless and the formation and development of the grain.The effects of La???on the above indicators of soybean populations at different growth stages were generally presented:seedling stage>flower ing and podding stage>seed-filling stage.Principal component analysis can also prove the above assertion.Through the above studies,it was found that the effects of La???on the reproduction rate,modules growth and respiration of soybean population decreased with the increase of population density;under the medium and high concentrations of La???,the inhibitory effect to soybean population was enhanced with the increase of La???concentration and the treatment time of La???.Synchronous observation showed that the degree of influence of La???on the above-mentioned indexes of soybean populations at different growth stages generally showed:seedling stage>flowering and podding stage>seed-filling stage.