EFFECT OF SOIL-PH ON MINERAL ELEMENT CONCENTRATIONS OF 2 ERYTHROXYLUMSPECIES

Erythroxylum coca var. coca Lam. (E. coca) and Erythroxylum novogranat ense var. novogranatense (Morris) Hieron (E. n. novogranatense) are tw o of four Erythroxylum species grown in the tropics of South America f or cultural medicines and the alkaloid benzoylmethylecgonine. In a pub lished study of biomass production over a soil pH range of 3.5 to 7.0, E. coca grew best at a pH equal to and below 5.5, and E. n. novograna tense grew best within the pH range of 4.7 to 6.0. Erythroxylum coca w as tentatively classified as more tolerant to metal toxicities [alumin um (Al) and manganese (Mn)] than E, n. novogranatense, however, concen tration patterns of mineral elements for E. coca and E. n. novogranate nse tissue have not been reported, nor have the mechanisms of differen tial acid-soil-tolerance been elucidated. In the current study, the ef fects of soil pH on concentrations of Al, calcium(Ca), copper (Cu), ir on (Fe), potassium (K), magnesium (Mg), Mn, and zinc (Zn) in leaves, s tems, and roots were investigated. At pH 3.5, roots of both species ac cumulated high concentrations of Al that decreased as soil pH increase d, however, there was no pH x species interaction. The highest concent ration of Ca was found in the leaves of both species, however, E. coca accumulated more Ca as soil pH increased than did E. n. novogranatens e. Manganese and Zn levels were highest in roots of both species (E. c oca and E. n. novogranatense); levels in all tissues decreased with in creasing pH. Manganese concentration was highest in roots of E. coca a nd Zn concentration was highest in tissues off. n. novogranatense. Cop per, Fe, K, and Mg levels were erratic with increasing pH, indicating that sufficient amounts of these nutrients are acquired at low pH leve ls. Root concentrations of Fe and K in E. coca increased markedly betw een pH 3.5 and 4.7. At pH 3.5, E. coca demonstrated no symptoms of min eral deficiency and/or toxicity, however, chlorosis, leaf distortion a nd root atrophy were prevalent at pH 6.5 and 7.0. By contrast, E. n. n ovogranatense demonstrated diminished growth and root atrophy at soil pH 3.5, whereas at pH 6.5 and 7.0, although biomass production was red uced, no symptoms of mineral deficiency and/or toxicity were present. The species obviously behave differentially at pH extremes and E. coca appears to be most tolerant of extremely acid soils; the two species may also differ in mineral sensitivities between the species at higher pH levels. Erythroxylum coca may compete more effectively with Al for Ca binding sites within the root, and may have greater internal toler ance of Mn, compared with E. n. novogranatense.