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A test of the applicability of the R* hypothesis of resource competition to higher plants.
GRACE, JAMES1, GUNTENSPERGEN, GLENN2, KEOUGH, JANET2, 1 2
ABSTRACT- The R* hypothesis predicts that superior nutrient competitors will be those that possess low minimum nutrient requirements and the ability to reduce nutrient concentrations to lower levels than their competitors. A particular suite of plant traits have been predicted to be associated with good nutrient competitors. The objective of this study was to determine if the R* hypothesis could be used to predict the performance of plants in mixture based on their properties in monoculture. To accomplish this, a number of experiments were performed to examine competitive dynamics and monoculture traits under greenhouse conditions. Only a portion of the predictions were met. Competitive success was positively correlated with total nitrogen uptake and negatively correlated with final sediment ammonia concentrations, suggesting that nitrogen reduction drove the competition process. Also as predicted, high allocation to roots and low nitrogen loss rates correlated with competitive success. However, other predictions were not met. Minimum nutrient requirements were inversely correlated with competitive success, while high maximal growth rates correlated with competitive success. Based on these findings, it appears that the R* hypothesis is not adequate as a framework for predicting competitive dynamics of rhizomatous, perennial plants. The discrepancy observed in this study between final resource reduction and minimum resource requirement is at odds with the equilibrium assumptions of R* and suggests that higher plant competition should be modeled as a nonequilibrium process.
KEY WORDS: competition, nutrients