Net photosynthesis, root respiration, and regrowth of Bouteloua gracilis following simulated grazing.

Net photosynthesis (P), root respiration (R), and regrowth of Bouteloua gracilis (H.B.K.) Lag. were examined in the laboratory over a 10-day period following clipping to a 4-cm height to simulate grazing by large herbivores. Net photosynthesis rates of tissue remaining immediately following defoliation were only about 40% as great as preclipping rates. Three days after clipping, P rates of defoliated plants had increased to values about 21% greater (per unit leaf area) than those of unclipped controls and remained at that level through Day 10. No statistically significant changes in R occurred following defoliation. Biomass of unclipped plants nearly doubled during the 10-day study period, while that of defoliated plants increased 67%. Over half the new growth of defoliated plants was allocated to new leaf blades and only 18% to new roots, while only 33% of the new growth of control plants was allocated to new leaf blades but 29% went to new roots. As a consequence of increased P rates and increased carbon allocation to synthesis of additional photosynthetic tissue following defoliation, net CO uptake per plant increased from 9% to 80% of that of the controls from Day 0 through Day 10.