Influence of Plant Density on the Growth of Prosopis glandulosa var. glandulosa and Buchloe dactyloides

Abstract

W. VAN AUKEN AND J. K. BUSH (Div. Life Sci., Univ. Texas at San Antonio, San Antonio, TX 78285). Influence of plant density on the growth of Prosopis glandulosa var. glandulosa and Buchloe dactyloides. Bull. Torrey Bot. Club 114:393-401. 1987.-Intra- and interspecific competition experiments were conducted in the greenhouse with seedlings of Prosopis glandulosa var. glandulosa Torr. (honey mesquite) and Buchloe dactyloides (Nutt.) Engelm. (buffalo grass). Growth of P. glandulosa seedlings by themselves, as measured by number of leaves, stem length, basal diameter, above-, belowground, and total biomass per plant, decreased as plant density increased. All of these parameters increased on a per pot basis. Root: shoot ratios increased as plant density increased. Above-, belowground, and total biomass per plant of B. dactyloides decreased with increasing B. dactyloides density in monoculture. Root: shoot ratios increased with increasing grass density. A single B. dactyloides plant did not significantly reduce above-, belowground or total biomass of P. glandulosa seedlings as compared to P. glandulosa grown by itself. However, B. dactyloides densities of two or more caused a significant decrease in all P. glandulosa biomass measurements. Root: shoot ratios for both P. glandulosa and B. dac- tyloides increased by a factor of two from the lowest to highest grass density when grown together. Slopes of log-log regressions of plant density and biomass for both intra- and inter- specific interactions were less than zero, showing that both intra- and interspecific competition occurred. Slopes of intra- and interspecific regressions for aboveground biomass of P. glandulosa were not significantly different. However, slopes of belowground and total biomass were steeper for interspecific competition than for P. glandulosa intraspecific competition. This suggests that B. dactyloides is a better competitor for soil resources than seedlings of P. glandulosa, especially at a high grass density. In addition, the presence of one seedling of P. glandulosa did not have any effect on the slope of regressions of above-, belowground or total biomass of B. dactyloides. Thus, P. glandulosa is probably not an invader of high density, highly productive B. dactyloides grasslands; rather, it is a colonizer of open, low-density areas.