Effects Of Silicon On Cadmium Morphology In Soil,physiological Characteristics Of Cucumber And Cadmium Absorption And Enrichment

The pot experiment was conducted to study the effects of silicon on Cucumber growth,photosynthesis,fluorescence parameters and after-effects of silicon on cadmium content in cucumber plants and cadmium morphology in soils under Cd stress on calcareous soils with cucumber(Jinlv 21^-10)as test material.（1）Under Cd stress,cucumber growth and development were inhibited,and the inhibitory effect was more obvious as the Cd concentration increased.Application of suitable concentration Si can effectively alleviate the toxic effects of Cd Stress on cucumber growth,improve cucumber plant height and plant fresh weight,and the root system has increased growth ability under the intervention of silicon,which improves the absorption of soil nutrients by cucumber plants,thus increasing the accumulation of substances in cucumber plants and then promoting cucumber growth and development.Si≥200 mg·kg^-1 significantly increased the above ground dry matter mass of plants under the stress of Cd5 concentration.（2）As Cd concentration increased,the net photosynthetic rate（Pn）,stomatal conductance（Gs）and transpiration rate（Tr）of cucumber leaves significantly decreased,and the intercellular CO₂（Ci）significantly increased.Si intervention effectively relieved the decrease of Pn,Gs,Tr and the increase of Ci.Si≥300 mg kg^-1 significantly alleviated the decline of Pn and Gs under Cd stress,while under Cd5 stress,the levels of Tr were significantly higher and Ci significantly lower under Si≥200 mg kg^-1.The total chlorophyll（Chla+b）content decreased with increasing Cd concentration,and the involvement of silicon alleviated the decrease.Under different silicon concentration gradients,carotenoid（car）content showed different variation trends when cadmium concentration increased.（3）In the single application of Cd,leaf F₀ significantly increased and Fv/Fm,Y（II）and q P significantly decreased as the Cd concentration increased.Silicon intervention suppressed the elevation of F₀ and slowed the decrease of Fv/Fm,Y（II）and q P.No significant difference in Fv / Fm was caused by Cd stress at different concentrations with Si≥300 mg kg^-1,and all were maintained at higher levels.When in silicon,Y（II）decreased less than when in silicon,but there was no significant difference among Cd3 or Cd5 treatments under stress.Showed that the intervention of Si increased the Y（II）value,alleviated the stress of Cd,and improved the efficient conversion ability of PSII light energy.At Cd5,q P values were significantly increased by 12.59%,18.93%,22.27% for Si2,Si3,and Si4 treatments,respectively,compared with Si0,while no significant difference was observed for Si0 compared with Si1.It indicated that the opening of the reactive center of PSⅡ could be strengthened by Si≥200 mg·kg^-1 when treated with high concentration of Cd5.（4）In the two stubble cucumber cultivation,the Cd contents in various organs of cucumber were as follows: Cd content in cucumber roots>Cd content in Cucumber stems>Cd content in cucumber leaves>Cd content in cucumber fruits.The Cd content in various organs of cucumber showed a decreasing trend with the increased Si concentration,in which the Cd content in each organ decreased in the order of cucumber fruit>cucumber leaf>cucumber stem>cucumber root.Among first stubble cucumber plants,the standard value could not be achieved with Si application of 300 mg·kg^-1 when the Cd content was 5 mg·kg^-1,while the Cd content in cucumber fruits with Si application of 400 mg·kg^-1 could be further reduced,and the safety standard value was reached below 0.05 mg·kg^-1.In the second stubble cucumber cultivation,continued Si plus Cd as well as continued Cd without Si,all decreased the Cd content in cucumber fruits with increasing Si concentration.But neither Si application up to 400 mg·kg^-1 could reduce the Cd content in cucumber fruit below the safety standard value of 0.05 mg·kg^-1.Si4cd5,continuous silicon plus cadmium treatment could reduce the cadmium content in cucumber fruit to 0.137 mg·kg^-1,which was 24%lower compared with 0.18 mg·kg^-1 of cucumber fruit cadmium content in the post silicon effect treatment.（5）Cd in exchangeable state and Cd in carbonate bound state were decreased by the addition of silicon,while Cd in ferromanganese bound state,Cd in organic bound state,and Cd in residue state were increased.In the first stubble,where Si was applied up to 400 mg kg^-1,Cd in the exchangeable state was significantly lower under the Cd3 treatment,Si≥300 mg kg^-1 under the Cd5 treatment,Cd in the exchangeable state in soils was significantly lower,The content of exchangeable Cd in soil under the second stubble plus Si plus Cd treatment was overall lower than that under the second stubble plus Cd treatment only,indicating that continued Si addition can effectively reduce the exchangeable Cd content in soil and reduce Cd uptake by cucumber plants.Because the soils themselves were calcareous soils and because sodium silicate readily formed complexes with ferric manganese bound state Cd,the Fe-manganese bound state Cd residue in soils after Si Fertilization,compared with the Fe-manganese bound state Cd residue in soils continuously treated with Si plus Cd,all increased with increasing Si concentrations,and the Fe-manganese bound state Cd residue in soils under both treatments did not differ greatly.The residual Cd residue ranged from 0.30 to0.36 mg kg^-1 in Cucumber soils with continued Si Cd addition for the second stubble,and from 0.22 to 0.26 mg kg^-1 in Cucumber soils with no Si continuously added Cd for the second stubble.It indicated that the post fertilization effect of Si fertilizer had a limited ability to fix Cd in the soil residue state.