Leaf net photosynthesis (Pn), conductance to water vapor, water potential, solar radiation penetration within the leaf canopy, and biomass production of mesa dropseed (Sporobolus flexuosus) was measured 4-, 18-, and 34-days following removal of one-half of all shoots. Pn rates of defoliated plants were 35% higher than leaves of similar aged leaves on control plants after 18 and 34 days. Daily integrated radiation penetration within the canopy of defoliated and control plants averaged 66 and 32 percent, respectively, of the total irradiance received in the open. Compensatory photosynthesis evident in this study was not due to changes in conductance or improvements in plant water status. There were no differences between treatments in leaf conductance, but on all three sample days, leaf water potential of partially defoliated plants were 20-30% more negative than those of control plants. In conclusion, compensatory photosynthesis may be a common response in defoliated range grasses despite the suboptimal environmental conditions common in the field.
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