Plant Adaptation in an Ecosystem Context: Effects of Defoliation, Nitrogen, and Water on Growth of an African C4 Sedge

Abstract

Clones of a C4 sedge, Kyllinga nervosa Steud., from a semiarid location in the Serengeti region of Tanzania were propagated vegetatively and grown at 12—h photoperiods, 30°C maximum daytime temperature and 15° minimum nighttime temperature, simulating conditions at the native site. Clipping height, clipping frequency, nitrogen concentration of the nutrient medium, and watering frequency were varied in an unbalanced factorial experiment. Plants were harvested after 5 mo of sustained treatment. Each yield component was principally regulated by a different environmental factor. Yield to grazers (amount clipped off) was controlled by nitrogen supply, yield to producers (residual biomass) was controlled by water, and yield to decomposers (litter and standing dead) was controlled by clipping height and nitrogen. Plant growth was stimulated by defoliation. Plants overcompensated for amounts removed at moderate defoliation at high nitrogen, undercompensated at severe defoliation, and just compensated under other conditions. Therefore, increments of energy flow to grazers can be additive in ecosystem budgets due to compensatory growth of affected plants. The most important mechanisms accounting for compensatory growth of K. nervosa were activation of plant meristems and stimulated rates of leaf elongation in defoliated plants. Allocation of residual plant biomass to various organs was virtually independent of environment, indicating genetic control of physiological processes tending to balance allocation over a broad environmental range.