Different Ph, Nitrogen Form And Ca (2 +) On Corn Root Morphological Development Of Nutrient Elements And Transport Impact

Solution culture experiments were carried out to explore the effects of some environmental factors, medium pH levels, nitrogen forms, Ca concentration and Cd on the distribution of Ca²⁺ in maize roots, the development of roots, the biomass of seedlings and the transport of nutrition elements and Cd. The results indicated that:(1) There was less Ca²⁺ in root cells under pH4.0 than under pH6.0. Low pH caused plasmolysis. Nitrate treatment led to less Ca²⁺ in the cells of wheat roots than ammonium treatment, especially in intercellular substances, cell wall and membrane. In the presence of ammonium, plasmolysis, loose of cell structures and cytoplasma outflow could be observed, which might due to Ca²⁺ in cell wall and membrane was replaced by NH₄⁺ and the structures of cell wall and membrane were destroyed. Moreover, low pH level aggravated the negative influence.(2) NO₃^--N promoted the growth of lateral roots of maize and biomass of seedlings. NH₄⁺-N stimulated the development of vascular cylinder, where xylem vessels elements developed early and had large radius, which caused the roots of maize treated with NH₄⁺-N showed larger mean diameter than that treated with NO3―-N. The reason for NH₄⁺ toxicity may be that NH₄⁺ with high concentration took place of Ca²⁺ in cell membrane simultaneously and further damaged the structures of cell membrane. Increase of Ca²⁺ in outer medium could alleviate to some extent the inhibitory effects of low pH and NH₄⁺-N on the development of maize roots.(3) Too much NH₄⁺ in xylem sap reduced biomass of maize treated with NH₄⁺-N. Uptake of NO₃^- heightened pH value of xylem sap. Mutual facilitation of Ca²⁺ and K⁺ uptake mainly manifested in total quantities. Transport rate of Ca²⁺ in xylem sap of maize treated with NH₄⁺-N was higher than that treated NO3―-N, though NO3― promoted the absorption of Ca²⁺. Under the conditions of low pH, high concentration of NH₄⁺and lack of Ca, the transport of nutrition ions in xylem sap relatively decreased, maybe because these stresses cut down the vitality of roots,...