Dynamic morphological plasticity in response to emergence timing in Abutilon theophrasti (Malvaceae)

Selections on emergence time might be conflicting, suggesting the existence of the optimal emergence time for plants. However, we know little about this and how morphological plasticity contributes to the strategies of plants in response to emergence timing. To better understand this issue in a dynamic perspective, we conducted a field experiment by subjecting plants of Abutilon theophrasti to four emergence treatments (ET1~ET4) and measuring a number of mass and morphological traits on them at different growth stages (I~IV). At day 50, 70 and/or final harvest, among all ET treatments, plants germinated in late spring (ET2) performed the best in total mass, spring germinants (ET1) and ET2 performed better in stem allocation, stem and root diameters than later germinants (ET3 and ET4); summer germinants (ET3) had the highest reproductive mass and allocation, while late-summer germinants (ET4) had the greatest leaf mass allocation, with greater or canalized leaf number and root length traits than others. Plants that emerged in late spring can maximize their growth potential, while those with either advanced or delayed emergence are still capable of adaptation via allocation and morphological plasticity. Early germinants (ET1 and ET2) preferred stem growth to leaf and reproductive growth, due to sufficient time for reproduction in growth season. With limited time for growth, plants emerged late may prefer to quicken leaf growth (indicated by increased leaf mass allocation and leaf number) at the cost of stem or root growth for complete life cycle, reflecting both positive and negative effects of delayed emergence.