石灰性土壤上HCO_3^-诱导花生缺铁失绿机制

Mechanisms of bicarbonate induced iron-deficiency chlorosis of peanut on calcareous soils

采用土壤-营养液结合的分根培养方法,研究了部分根系供应HCO- 3或铁对花生铁营养的调控及其作用机制。结果表明,对花生部分根系供应HCO- 3或铁可以调控花生的铁营养,仅供HCO- 3可以诱导缺铁,而只供铁能矫正失绿,同时供应HCO- 3和铁时则不引起失绿。在花生新生叶失绿和复绿的过程中,其中的活性铁含量和全铁含量也有相应的消长。当花生表现缺铁失绿症状时,地上各部分的全铁含量显著降低,而土中根的全铁含量不降低、质外体铁含量升高。在HCO- 3存在的条件下,不同部分根系的铁( )还原酶活性因其生长介质而不同,营养液中根系的铁( )还原酶活性降低而土中根的铁( )还原酶活性不受影响。当花生表现缺铁失绿症状时,土壤中HCO- 3含量升高,有效铁含量不高,p H值无变化。因此,本试验证实了石灰性土壤上的高HCO- 3含量,主要是降低了花生地上部的铁含量而引起失绿,而且花生缺铁失绿又导致土壤HCO-

Dicotyledonous plants are prone to iron-deficiency chlorosis when grown on calcareous soils. This nutritional disorder problem occurs widely and can be a limiting factor for crop yield and quality. The main reasons for the disorder are high pH and high bicarbonate (HCO^-_3 ) concentration in soil solution. It has been shown that HCO^-_3 induces chlorosis by suppressing iron uptake and/or translocation in plants, although the relationship between HCO^-_3 accumulation, iron-deficiency chlorosis and rhizosphere properties remains unclear. The objectives of the present study were to investigate (i) the effect of HCO^-_3 and Fe supply on chlorosis and iron nutrition of peanut (Arachis hypogaea L., Luhua c.v.), (ii) the relationship between chlorosis, apoplastic iron concentration in roots and the activity of Fe(Ⅲ) reductase in roots, (iii) the effect of chlorosis on the properties of rhizosphere and bulk soil. Peanut was grown in a two-chamber pot, with the top chamber being filled with a calcareous soil and the bottom one with nutrient solution. The two chambers were separated by a plastic film membrane, which allowed roots to penetrate but not the exchange of solutes. Plants were grown in this system under four treatments: (CK) no additions of HCO^-_3 or Fe to either soil or nutrient solution, (Ⅰ) additions of 1500 mg·kg^(-1) HCO^-_3 to soil and 0.1mmol·L^(-1) Fe to nutrient solution, but no addition of HCO^-_3 to nutrient solution, (Ⅱ) additions of 10 mmol·L^(-1) HCO^-_3 and 0.1mmol·L^(-1) Fe to nutrient solution but not to soil, and (Ⅲ) addition of 10 mmol·L^(-1) HCO^-_3 but not Fe to nutrient solution and no addition to soil. The results showed that the Fe nutritional status was influenced significantly by the HCO^-_3 and Fe treatments to parts of the root system. No chlorotic symptoms were observed in CK. Addition of HCO^-_3 to soil (treatment (Ⅰ) induced chlorosis initially, but the symptoms disappeared once the roots penetrated into the nutrient solution supplied with Fe. Additions of both HCO^-_3 and Fe to nutrient solution (Treatment Ⅱ) did not induce chlorosis. In treatment Ⅲ, plants were normal initially, but later young leaves became chlorotic after roots reached the nutrient solution. The occurrence of chlorosis or the re-greening of young leaves coincided with the changes in the active and total Fe concentrations. However, Fe concentration in roots (collected from the soil chamber) did not decrease in the chlorotic plants, whereas the concentration of root apoplastic Fe increased. Addition of HCO^-_3 to either soil or nutrient solution decreased the activity of-on Fe (Ⅲ) reductase in the roots collected from the nutrient solution chamber, but not in those from the soil chamber. Iron-deficiency chlorosis induced in treatment Ⅲ was found to increase the concentration of HCO^-_3 in the rhizosphere soil. It is concluded that HCO^-_3 inhibited Fe translocation from roots to shoots, and iron-deficiency chlorosis could also lead to a higher HCO^-_3 concentration in the rhizosphere soil, thus exacerbating the iron-deficiency disorder.