NUTRIENT SALTS AND THE TOXICITY OF BLACK-LAYER INDUCED BY CYANOBACTERIA AND DESULFOVIBRIO-DESULFURICANS TO AGROSTIS-PALUSTRIS

Cyanobacteria and Desulfovibrio desulfuricans can interact to form a s ubsurface black-layer in high-sand content golf greens that impairs in ternal water drainage and results in the decline of the Agrostis palus tris turfgrass on the green. Research was initiated to evaluate the ef fect of mineral salts (sulfur, iron, Lime) and fructose (a soluble car bohydrate) added to a balanced nutrient salts control solution on the development and toxicity of black-layer to the growth of A. palustris. The various nutrient salts combinations were applied to single isolat es of cyanobacteria and D. desulfuricans in nonblack-layered sand, and to the combination of cyanobacteria and D. desulfuricans (necessary f or black-layer development) in black-layered sand. Dry weights of A. p alustris treated with the salts control decreased with individual isol ates of cyanobacteria and more so in the blackened sand produced by th e combinations of cyanobacteria and D. desulfuricans. The addition of sulfur to the salts control increased dry weights of A. palustris grow ing with single isolates of cyanobacteria and in the sand blackened by the combinations of cyanobacteria and D. desulfuricans compared with the salts control; dry weight decreased in response sulfur only in non blackened sand with D. desulfuricans alone. The addition of iron to th e salts control produced the greatest increase in dry weight relative to the salts control among all single and combined microorganisms, exc ept for D. desulfuricans. The addition of lime or fructose to the salt s control decreased dry weight among plants growing in the no-organism control, with D. desulfovibrio alone, and with individual isolates of cyanobacteria relative to the salts control. Dry weights in response to lime and fructose in sand blackened by the combination of cyanobact eria and D. desulfuricans remained unchanged or decreased relative to the salts control. Growing roots of A. palustris cleared the blackenin g in sand and showed gold-colored cortical cells with blackened cell w alls and vascular cylinders. The observations are discussed relative t o the role of the various salts on the toxicity of D. desulfuricans to A. palustris in black-layered and nonblack-layer sand.