| Cadmium(Cd)is an extremely poisonous element which can affect human health through the food chain after being absorbed by crops.The main sources of Cd contamination in agricultural soil include industrial waste,sewage irrigation and atmospheric deposition.Wheat is one of the major food crops in China,it has the strong ability of Cd accumulation.Thus,to ensure the food safety,it is of great importance to reduce the Cd concentration in edible and feeding parts of wheat.Zinc(Zn)is an essential microelement for wheat,and has similar chemical properties with Cd.Therefore,complex interactions between Cd and Zn may occur in the soil-plant system.Nitrogen(N)is the key component of mental transport carries,which affects the transportation of Cd or Zn and regulates the interactions between Cd and Zn in plants.The pot experiments were carried out in 2020-2021 and 2021-2022,and wheat cultivar Yangmai 25 were used in both cropping seasons.The main plots were N application levels of normal N fertilizer and reduced N fertilizer.The split plots contained the control,soil Zn application,soil Cd contamination and the combination of Zn application and Cd contamination.At plant maturity,the aboveground of wheat were separated into seventeen parts(organs),and Cd/Zn concentration and accumulation in different parts of wheat were determined.The objective of the study is to investigate the effects of N fertilizer reduction and soil Zn application and their interactions on wheat growth,physiology,elements concentration and accumulation in different parts of wheat under Cd contamination,and to investigate the influences of aging effects of heavy metals in soil on Cd,Zn and their interaction in wheat.The main results were as follows:1.Compared with no Cd contamination,5 mg·kg-1 soil Cd contamination significantly increased the Cd concentration and accumulation in different parts of wheat in both cropping seasons,but had no significant effects on leaf photosynthetic characteristics,chlorophyll fluorescence characteristics,plant growth and yield traits.The increase of the Cd concentration in different parts of wheat in the second season(+3～24 times on average)was less than that in the first season(+10～57 times).The Cd accumulation in different parts of wheat was affected by soil Cd contamination showed the same trend.Furthermore,Cd contamination significantly decreased the concentration of manganese(Mn),potassium(K)and magnesium(Mg)in all organs of wheat,and the Zn concentration and accumulation in wheat leaves were significantly decreased.This pattern occurred in both cropping seasons.2.Compared with no soil Zn application,150 mg·kg-1 soil Zn application increased the maximal quantum yield of PSII photochemistry(Fv/Fm)by 2%(P<0.05)and 0.5%(P=0.09)in first season and secondary season,respectively.And significantly increased the spikes per plant that were increased by 10%and 11%in first season and secondary season,respectively.As a result,wheat grain yield was increased by 7%and 10%in first season and secondary season,respectively.Soil Zn application significantly increased the Zn concentration and accumulation in different parts of wheat,the increase of the Zn concentration in different parts of wheat in first season(+23～56%)was less than that in secondary season(+30～594%).The Zn accumulation in different parts of wheat was affected showed the same trend.Furthermore,soil Zn application significantly decreased the Cd concentration and accumulation in different parts of wheat in both cropping seasons,but the decrease in different parts of wheat in first season(-2-38%)was less than that in secondary season(-23～56%).The Cd accumulation in different parts of wheat showed the same trend.Besides,soil Zn application significantly decreased the concentration of Mn and phosphorus(P)in all organs of wheat in both cropping seasons.3.N reduction in late growing stage of wheat significantly decreased the leaf SPAD value,Fv/Fm,net photosynthetic rate(Pn)at the heading stage and significantly decreased the wheat length,tillering,spikes,kernels,1000 kernels mass,aboveground biomass and harvest index(HI)in both cropping seasons.As a result,wheat grain yield was decreased by 36%and 48%in the first season and secondary season,respectively.Both cropping experiments showed that N reduction significantly decreased the Cd concentration and accumulation in wheat.The Cd concentration of wheat grain was significantly decreased by 12%and 18%in first season and secondary season,respectively.And the accumulation of wheat spikes was significantly decreased by 27%and 42%in first season and secondary season,respectively.But there existed a difference in other parts of wheat between two cropping seasons that N reduction significantly decreased the Cd concentration in glume,sheathl,leafl and leaf2 of wheat in first season while significantly decreased the Cd concentration in leaf1,sheath2,sheath3 and the remanent stem and sheaths of wheat in secondary season.Besides,N reduction significantly decreased the concentration of copper(Cu),iron(Fe)and Mg in wheat while the concentration of Mn and P in wheat was significantly increased in both cropping seasons.4.Compared with N reduction or soil Zn application alone,the Cd concentration of wheat grain decrease greater by the combined of N reduction and soil Zn application.The Cd concentration in wheat grain was significantly decreased by 34%and 36%in first season and secondary season,respectively.The other parts of wheat showed the same trend.In conclusion,5 mg·kg-1 soil Cd contamination significantly increased the Cd concentration and accumulation in different parts of wheat while had no significant effects on the leaf photosynthetic characteristics,plant growth and yield traits in both cropping seasons.Soil Zn application or N reduction could effectively decrease the Cd concentration of wheat,especially in wheat grain.Furthermore,the Cd concentration was decreased greater by the combined of N reduction and Zn treatment.Besides,the aging effects in soil effectively decreased the concentration of Cd/Zn,and affect the interaction between Cd and Zn. |
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