Predicting Compensatory Growth and Reproduction in Agricultural Weeds Using a Plant’s Growth Rate Trajectory: A Test with Defoliation of Abutilon theophrasti

A plant’s capacity to compensate for pest damage as a function of resource availability needs to be predictable in order to apply biocontrol agents effectively. In this research, it was hypothesized that a weedy plant species’ capacity to compensate for defoliation is related to how resource availability affects a plant’s growth trajectory. Growth rate trajectory is defined as the percent change in relative growth rate or the slope of a plant’s relative growth rate. 90 Abutilon theophrasti, a common weed species, in cultivated fields of corn and soybean, grew in a greenhouse for 70 d under three nitrogen (N) fertilization treatments. “Unfertilized” plants were not fertilized, “bulk” fertilized plants received 0.6 g N on day 15 and “exponential” fertilized plants received a total of 0.6 g N supplied at an exponential rate of 10% per day with a starting concentration of 0.02 g N on day 15. On day 25, 15 plants in each N treatment had 75% of total leaf area removed. Biomass and reproductive compensation were determined after 50 d and 70 d of growth. Results showed that bulk plants had the greatest absolute growth, but also the greatest decline in growth rates and the least capacity for compensation. Unfertilized plants had the lowest absolute growth, but declines in growth rates were similar to bulk plants with only a slightly greater compensatory capacity. Exponential plants had intermediate absolute growth, but the least decline in growth rates and the greatest capacity for compensation. This experiment indicates that a plant’s growth rate trajectory, and not high or low relative growth rates or N availability per se, can be used to predict a weedy plant’s capacity to compensate for herbivory, and has implications for biocontrol of weedy species.