DIFFERENTIAL RESPONSES OF C-3 AND C-4 GRASSES TO MYCORRHIZAL SYMBIOSIS, PHOSPHORUS FERTILIZATION, AND SOIL-MICROORGANISMS

The responses of 5 C4, warm-season and 5 C3, cool-season tallgrass prairie grasses to P fertilization, mycorrhizae, and soil microorganisms were compared. The warm-season grasses responded positively to mycorrhizae or to P fertilization, but mycorrhizal plants did not respond to P. The soil microflora reduced mycorrhizal plant dry weight and root colonization. Cool-season grasses did not respond to mycorrhizae or P fertilization. Soil microorganisms did not suppress cool-season plant growth, but root colonization was reduced in nonsterile soil. For the warm-season grasses there was an inverse relationship between mycorrhizal root colonization and P fertilization and a positive relationship between root colonization and plant dry weight. For the cool-season grasses there was also an inverse relationship between root colonization and P fertilization, but the relationship between root colonization and plant dry weight was negative. In both the warm-season and cool-season grasses, low levels of mycorrhizal root colonization persisted even when P fertilization was sufficient to eliminate mycorrhizal efects on plant growth. -from Authors