Dynamic reproductive plasticity in response to emergence time and population density in Abutilon theophrasti (Malvaceae)

Emergence time and population density both have important influences on plants, but their interactive effects have not been well understood, especially on plant reproduction in dynamic patterns. A field experiment was conducted by subjecting plants of Abutilon theophrasti Medicus (Malvaceae) to four treatments of sowing dates (emergence periods, ET 1 –ET 4 ) and three treatments of (low, medium and high) planting density, and population reproductive traits such as the number of reproductive individuals in total and of different reproductive ranks (RR) were observed, and mean values and among-individual variation in these traits were calculated. Results showed that either an advance or delay of emergence can increase the percentage of flowering or fruiting individuals of the populations. Compared to low density, high density reduced the percentage of flowering individuals and the number of fruits per individual at day 110, with little effect on the percentage of fruiting individuals, whereas medium density promoted the reproduction, for populations of ET 1 . Density effects were only significant for the plants that emerged early, and increased density reduced the responses of plants to emergence time. The results revealed the strategies of A. theophrasti in dealing with complex biotic environmental changes at the population level: advanced or delayed emergence can result in shortened vegetative growth and earlier reproduction, whereas increased density tended to decrease the percentage of flowering individuals while maintaining that of fruiting ones stable and effects density depend on the strength of inter-plant interactions.