EFFECTS OF EXCESS MANGANESE ON MINERAL UPTAKE IN MYCORRHIZAL SORGHUM

Associations between vesicular-arbuscular mycorrhizal (VAM) fungi and manganese (Mn) nutrition/toxicity are not clear. This study was conduc ted to determine the effects of excess levels of Mn on mineral nutrien t uptake in shoots and roots of mycorrhizal (+VAM) and nonmycorrhizal (-VAM) sorghum [Sorghum bicolor CL) Moench, cv. NB9040]. Plants coloni zed with and without two VAM isolates [Glomus intraradices UT143-2 (UT 143) and Gl. etunicatum UT316A-2 (UT316)] were grown in sand irrigated with nutrient solution at pH 4.8 containing 0, 270, 540, and 1080 mu M of added Mn (as manganese chloride) above the basal solution (18 mu M). Shoot and root dry matter followed the sequence of UT316 > UT143 > -VAM, and shoots had greater differences than roots. Shoot and root c oncentrations and contents of Mn, phosphorus (P), sulfur (S), potassiu m (K), calcium (Ca), magnesium (Mg), iron (Fe), zinc (Zn), and copper (Cu) were determined. The +VAM plants generally had higher mineral nut rient concentrations and contents than -VAM plants, although -VAM plan ts had higher concentrations and contents of some minerals than +VAM p lants at some Mn levels. Plants colonized with UT143 had higher concen trations of shoot P, Ca, Zn, and Cu and higher root Mg, Zn, and Cu tha n UT316 colonized plants, while UT316 colonized plants had higher shoo t and root K concentrations than UT143 colonized plants. These results showed that VAM isolates differ in enhancement of mineral nutrient up take by sorghum.