Role of phosphorus on the biogeochemical behavior of cadmium in the contaminated soil under leaching and pot experiments

Phosphorus(P)is involved in various biochemical reactions in plant growth,so it is beneficial to plants growing in soils contaminated by metals,including cadmium(Cd).However,few studies have reported on the mechanistic roles of P in mitigating Cd toxicity to ryegrass root,and especially in alleviating the disruption of the mitochondrial function of living cells.In this study,the physiological and biochemical mechanisms associated with ryegrass growth under various Cd and P treatments were investigated using leaching and pot systems.The concentration of Cd in soil leachates showed a significantly positive relationship with redox potential(P<0.05),but negative relationship(P<0.05)with leachate pH values and dissolved organic carbon(DOC),indicating that exogenous P addition(as H_(2)PO_(4)*)may decrease Cd leaching from contaminated soil.Compared to the control(without P addition),the cumulative Cd content was reduced by 53.3%and 64.5%in the soil leachate with exogenous P application(20 mg/L and 80 mg/L),respectively.Notably,application of P decreased the Cd concentrations in the symplastic fractions and increased the Cd concentrations in the apoplastic fractions in root tips,which may help to alleviate Cd stress to the protoplast.Moreover,exogenous P was found to play a positive role in mitochondrial function and Ca^(2+)variation in root cells under Cd stress,which provides novel insights into the mechanisms of exogenous P in alleviating plant Cd injury.

Contrasting behaviors of^(210)Po,^(210)Pb and^(234)Th in the East China Sea during a severe red tide:Enhanced scavenging and promoted fractionation

^(210)Po,^(210)Pb,and^(234)Th were determined in water columns of the East China Sea(ECS)to investigate their biogeochemical behaviors during a severe red tide event.Dissolved^(210)^(210)radionuclides were influenced by particle content effect and particle composition based on distribution coefficient(Kd)vs.total suspended matter(TSM)content and Kd vs.ratios of particulate organic carbon and total suspended matter contents(POC/TSM content ratios).The peaks of mass specific activities of^(210)Po,^(210)Pb,and^(234)Th indicated that degraded particles could have an intensified enrichment ability for radionuclides compared with the surficial suspended matters.Fractionation factor of^(210)Po and^(210)Pb(FPo/Pb)(>1)and fractionation factor of^(210)Po and^(234)Th(FPo/Th)(>1)were much higher at algal blooming regions than that at non-blooming stations,indicating that algal blooms promoted the fractionation of^(210)Po against^(210)Pb and^(234)Th,and proving that^(210)Po exhibited a stronger affinity for biogenic particles than^(210)Pb and^(234)Th when POC content increased in the sea.POC/^(210)Po,POC/^(210)Pb and POC/^(234)Th ratios(content/activity ratios)sharply decreased with depth in both algal bloom and non-bloom stations.The outbreak of algal bloom promoted the complexity of suspended particles and increased the variability of POC/tracer ratios(content/activity ratios)in the different depth of the shallow seas.More considerations should be taken to the difficulty of the selection of export interface and the suitable tracers when algal blooming occurs.