INDUCED MICRONUTRIENT TOXICITY IN TOUCHDOWN KENTUCKY BLUEGRASS

The growth of turfgrass may be affected by excess levels of micronutri ents. The objectives of this study were to determine changes in growth responses, leaf pigmentation, and chloroplast structure of Kentucky b luegrass (Pea pratensis L. cv. Touchdown) as affected by elevated leve ls of micronutrients. Plants were established in peat-lite mix in 11-c m pots using a standard nutrient solution and were thereafter constant ly fertilized with nutrient solutions supplemented with individual tre atments of 0.5, 1, 2, 4, 6, 8, or 12 mM of boron (B), chloride (Cl), c opper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), or zinc (Zn) f or 7 wk. The control solution had (in mu M) 20 B, 0.5 Cu, 40 Fe, 10 Mn , 0.5 Mo, and 4 Zn. The lowest micronutrient concentrations that showe d visual toxicity symptoms were 0.5 mM B, 12 mM Cl, 1 mM Cu, 4 mM Fe, 0.5 mM Mo, or 4 mM Zn. A reduction in dry matter yield was evident whe n the nutrient solution contained 2 mM B, 4 mM Cu, 2 mM Mo, or 4 mM Zn . Elevated levels of Cl, Fe, or Mn did not alter the biomass yield. Ch lorophyll-a (Chl-a), chlorophyll-b (Chl-b), and carotenoid contents de creased as B concentration increased. Chlorophyll (Chl) content, parti cularly that of Chl-b, increased with elevated levels of Fe. The alter ed Chl-b levels induced by Fe correlated with increased levels of ligh t harvesting chlorophyll (LHC) apoproteins and granal membrane accumul ations. The loss of Chi in the B and Mo treatments correlated with dec reased stroma membrane level and smaller chloroplast size, respectivel y. A linear relationship between the tissue and nutrient-solution conc entration existed for each micronutrient, suggesting a passive uptake by the plants. Findings of this study may be used in identifying alter ed growth and physiological characteristics of Kentucky bluegrass caus ed by supraoptimal levels of micronutrients.