The Effect of Phytophagous Nematode Grazing on Blue Grama Die-off

Abstract

Nematode populations were sampled in ungrazed and heavily grazed areas in northeastern Colorado under patches of healthy, senescing, and dead blue grama to test the hypothesis that phytophagous nematodes may cause the senescence. Densities of plant parasites were significantly different under the 3 plant types. Live blue grama supported the highest numbers (1.2 X 10^6 m2) and dead blue grama, the lowest (2 X 10^5 m2). Bacterial feeding nematodes also varied significantly with plant type. Highest densities were found under senescing plants (2.4 X 10^6 m2) and lowest densities were under dead plants (7 X 10^5 m2). Total densities were slightly but insignificantly lower in the heavily grazed area. Scarlet globemallow and fringed sagewort supported lower populations of both plant parasites and bacterial feeders than did live blue grama. The densities under live blue grama were not unusually high and well within the values reported in the literature for arid grasslands. Thus, nematode root grazing may decrease net primary production but we conclude that nematodes themselves were not the major cause of the die-off.