Morphological Characterization and Defoliation Responses of Selected Schizachyrium scoparium Genotypes

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Abstract
Allocation priorities before and after a severe defoliation were studied in a controlled environment for four genotypes of Schizachyrium scoparium selected for extremes in leaf length and tillering rate. Rates of leaf appearance for young tillers with 3-6 leaves were uniform and not correlated with fluctuations in leaf length within genotype, but were significantly lower for the long-leaved relative to the short-leaved genotypes. Rates of leaf elongation and leaf area expansion were generally correlated with fluctuations in leaf length within genotypes but not among genotypes. Nondefoliated tillers with 4-6 leaves of the slow-tillering genotypes produced more and longer roots than tillers of the rapid-tillering genotypes. This observation is reasonably explained by increased availability of carbon resources for root growth in slow-tillering genotypes. However, root growth following defoliation was significantly greater and shoot growth was significantly less for the long-leaved as compared to the short-leaved genotype, irrespective of tillering rate. It is suggested that rates of leaf elongation and carbon allocation following defoliation are genotypically determined, the latter providing important variation in natural populations for partitioning by the selection pressures of intense herbivory.