Combined Effects Of Nanoplastic And Plastic Additives On Crop Seedling Growth And Rhizosphere Behaviors

Experiencing the aging process,the abandoned plastic garbage release microplastics（MPs）and nanoplastics（NPs）,and simultaneously plastic addictives（PAs）also released into the environment.Some studies have reported the effects of MPs on land plants,but the mechanism of seed germination under the exposure of NPs is still unclear.Additionally,the synergistic effect of NP and PA on terrestrial plants is still unclear.Roots are rich in organic matter,and soil enzymes are catalysts of soil metabolism,which plays an important role in the field of soil environment.Therefore,this paper studied the seed germination mechanisms for tomatoes,rice,and corn,and explore the influence of jointly exposed by organic（Di（2-ethylhexyl）phthalate,DEHP）and inorganic（Cadmium,Cd）plastic additives and PSNPS to C₃（tomato）,C₄（corn）crops and their root soil enzymes activity.The main conclusions are as follows:（1）PSNPs increased the germination rate of tomatoes at low concentrations but inhibited it at high concentrations,and do not affect the final germination rate of tomatoes.PSNPs（1.0g/L）significantly increased the alpha-starch activity in tomato seeds by 35.5%,promoted starch decomposition（33.4%）,and more soluble sugar produced（seaweed sugar and citric acid content increased by 26.5,26.5 and 45.7%,respectively）,promoted the metabolism of amino acid and the tricarboxylic acid cycle.PSNPs（0.1,1.0 g/L）significantly increased rice germination rates（24.9,30.4%）and promoted rice root extension（11.2,43.9%）.PSNPs（1.0g/L）significantly increased the expression of water channel protein gene（OSPIP1;1 and OSPIP1;3）67.5 and 50.0%,respectively.PSNPs（1.0 g/L）promoted water absorption and protein hydrolysis in rice（soluble protein content decreased by 19.4%）,promoted rice amino acid metabolism and tricarboxylic acid cycle,and increased the content of citrate,cis-aconitic acid,and 2-isopropylmalic acid in rice seeds by 74.7,153.9,and 32.4%,respectively.PSNPs（1.0 g/L）promoted corn seed take roots by 21.8%,but it had no significant effect on the germination rate of corn seeds.PSNPs（1.0 g/L）increased theα-amylase activity of corn by427.5%,and promoted corn seed starch decomposition（starch content decreased by 34.9%）.The metabolomics analysis results indicated that PSNPs primarily affected starch and sucrose metabolism,glyoxylate and dicarboxylic acid metabolism,amino acid metabolism,and tricarboxylic acid cycle in corn seeds.The content of maltose,trehalose,methylmaleic acid,L-threonine,leucine valine,2-isopropyl malate and glyoxylic acid in corn seeds increased by152.3,112.3,27.6,50.0,78.6,262.1 and 27.7%,respectively.（2）The effect of PSNPs on tomato photosynthesis was not significant,but when the exposure concentration was 1.0 g/kg,it significantly reduced the maximum photochemical quantum yield（Fv/Fm）of maize leaves,and reduced the intrinsic light energy conversion efficiency in PSII reaction center of maize.DEHP（10 mg/kg）significantly reduced the maximum fluorescence coefficient（Fm）,Fv/Fm and photochemical quenching intensity（q P）in tomato leaves,reduced tomato photosynthetic activity,but had no significant effect on maize photosynthesis.The combined exposure of PSNPs reduced the inhibitory effect of DEHP on tomato photosynthesis,but the effect on maize photosynthesis was still not significant.PSNPs mainly inhibited alkaline phosphatase activity in tomato and maize rhizosphere soil,in addition,inhibited sucrase activity in maize rhizosphere soil,and increased urease and catalase activities.DEHP inhibited the activities of sucrase,urease and alkaline phosphatase in the rhizosphere soil of tomato and corn,but increased the activity of soil catalase.The combined exposure of PSNPs reduced the inhibitory effect of DEHP on alkaline phosphatase activity in tomato rhizosphere soil,and enhanced its inhibitory effect on sucrose enzyme in maize rhizosphere soil.Both PSNPs and DEHP promoted the transfer of nutrients（phosphorus,potassium,sodium,magnesium,and calcium）from the underground to the aboveground in tomatoes,but inhibited the transfer of nutrients in corn.DEHP exposure significantly reduced tomato plant height,aboveground and underground biomass（63.9,84.6,and 86.8%）,but had no significant impact on maize.The combined exposure of PSNPs promoted the underground to aboveground transfer of DEHP in crops,inhibited the stress effect of DEHP on crop roots,and increased the underground biomass of tomato and corn by 301.5 and 31.5%,respectively.This may be due to the increase in crop root length,root surface area,and root tips number.（3）Unlike DEHP,Cd had no significant effect on tomato photosynthesis and enzyme activity of rhizosphere soil.Similar to DEHP,Cd inhibited the activities of sucrase and alkaline phosphatase in the maize rhizosphere soil（17.1 and 31.4%）,increased the activity of catalase（6.5%）,promoted the transfer of nutrients from the underground to the aboveground in tomatoes,and inhibited the transfer of nutrients in maize.Unlike the combined effects of DEHP and PSNPs,the combined exposure of PSNPs promoted the underground to aboveground transfer of Cd in maize（TF and BCF increased by 73.7 and 65.2%,respectively）,but inhibited the underground to aboveground transfer of Cd in tomato（TF and BCF decreased by 30.5 and43.3%,respectively）.In addition,PSNPs reduced the inhibitory effect of DEHP on tomato photosynthesis（Fm value increased from 18139.5 to 21931.5;Fv/Fm increased from 0.485 to0.554）,while Cd had no significant effect on photochemical quenching intensity in tomato leaf（a decrease of 10.7%,p>0.05）.However,under the combined exposure of PSNPs and Cd,tomato leaf photochemical quenching intensity significantly decreased by 18.5%（p<0.05）.Therefore,PSNPs alleviated the growth inhibition of DEHP on tomatoes and enhanced the growth inhibition of Cd on tomatoes.