An ecophysiological approach was used to determine if competition can be detected among plants in a recently abandoned old-field and in a native tallgrass prairie in northeastern Kansas. In situ photosynthetic parameters and water potentials (Ψ) of target plants were measured 1-2 d after neighbor (intra- and interspecific) removal as well as 1-4 weeks later, and compared with values for plants with neighbors. Only two of the six study species (four old-field and two prairie species) responded to removal of neighboring plants, and only after several weeks had elapsed. Net photosynthetic rates (PN) and stomatal conductances (gs) of Ambrosia trifida in an old-field increased after removal of both intra- and interspecific neighbors. For Apocynum cannabinum, another old-field species, PN of target plants without neighbors was significantly higher than that of target plants with neighbors. For both these species, values of Ψ were not different between target plants with and without neighbors, suggesting that increased availability of nutrients may have been responsible for the observed ecophysiological responses. Though numerous past studies indicate that competition is a major factor influencing plants in old-field and in prairie communities, the experimental approach used in this study revealed that neighbor removal had only limited effects on ecophysiology of the target plants in either community. and F. Norman, C. E. Martin.
The effects of intra- and interspecific competition on growth, net photosynthetic rate (/^n), intemal CO2 concentration (cj), leaf conductance to CO2 (gi), and xylem leaf water potentials Q¥) were investigated among well-watered seedlings of the old-field species Abutilon theophrasíi. Ambrosia tri/ida, and Helianíhus annuus. In all comparisons, *F values of the target plants were unaffected by the presence of neighbors. On the other hand, revealed inhibitory effects of neighbors on A. theophrasíi and H. annuus. The above- and belowground biomass of all species was reduced in the presence of neighbors. Hence both inter- and intraspecific competition among seedlings may be important in influencing community stiucture in old-field communities.