RESPONSE OF THE ANNUAL ABUTILON THEOPHRASTI MEDIC. (MALVACEAE) TO TIMING OF NUTRIENT AVAILABILITY

Because resource variability is likely to be high in disturbed environments, colonizing species should be opportunistic in their abilities to use resources at any time during the growing season. We examined the effects of timing of nutrient availability on seed quantity and quality in the colonizing annual Abutilon theophrasti. Plants were grown under six different nutrient treatments involving additions of different size, frequency and timing but having the same total amount of nutrients in all treatments. The plants showed an opportunistic response, being able to use nutrients supplied at different times for reproduction. However, when nutrient availability was delayed until fruit maturation had begun, seed number and total seed weight were reduced, production of mature fruits was delayed, and seed P concentrations were reduced. Seeds from the first two fruits of the plants had higher N concentration (mg/g), higher N content (mg/seed), lower P concentration, higher K content, and higher mean seed weight.