EFFECTS OF THE ROOT-FEEDING NEMATODE TYLENCHORHYNCHUS-CLAYTONI ON GROWTH AND LEAF GAS-EXCHANGE OF BOUTELOUA-GRACILIS (GRAMINEAE)

Shoot, root and tiller production, net photosynthetic rates, transpiration rates, and biomass allocation patterns of Bouteloua gracilis (blue grama) were compared among controls and plants inoculated with the ectoparastic nematode Tylenchorhynchus claytoni. Total nematode populations increased slowly but number per gram of root biomass remained relatively constant since root biomass increased as well. Nematode densities (1,500-2,000 per g root) were similar to those observed in native North American grasslands. However, calculated nematode consumption exceeded 1% of root production during only one sampling period. No significant differences were observed between control and inoculated plants for any of the measured parameters. These results suggest that T. claytoni has less effect on primary production-related processes than might be assumed from estimates of annual consumption by root-feeding nematodes in grasslands. However, the total impact on system productivity will be a function of the density of all plant-parasitic nematodes, their host-parasitic relationships and other environmental stresses.