Effects of Defoliation and Nematode Consumption on Growth and Leaf Gas Exchange in Bouteloua Curtipendula

Abstract
Bouteloua curtipendula (sideoats grama) plants were grown in soil with and without the root-feeding ectoparasitic nematode Tylenchorhynchus claytoni. Half the plants in each treatment were defoliated at weekly intervals. Replicates from each of the 4 treatments were harvested 7, 36, 65 and 95 d after planting and analyzed for shoot and root biomass and tiller number. Before final harvest, rates of net photosynthesis (Pn) and transpiration were measured on individual leaves of 7 plants from each of the 4 treatments. Root biomass, shoot biomass, and tiller number were significantly decreased by either defoliation or nematode feeding, and combined defoliation and root feeding reduced growth more than either treatment alone. Fine roots were reduced more by nematodes than by defoliation. Rates of Pn and transpiration at final harvest were two or three times higher in defoliated plants than in nondefoliated plants, but there was no significant (P > 0.05) difference in Pn or transpiration between plants with and without nematodes.