Neither advanced nor delayed germination is optimal for performance – dynamic morphological plasticity in response to germination timing in Abutilon theophrasti (Malvaceae)

How plants respond to germination timing via morphological plasticity is not well documented, in spite of its importance for understanding plant strategies in dealing with natural environmental challenges of complicacy, especially in the perspective of the entire life cycle of plants. To address this issue, we conducted a field experiment with Abutilon theophrasti by growing plants in four periods, as four germination treatments (GT1~GT4), before measuring a number of mass and morphological traits on them at three (or four) growth stages (EX, I~III). Results the optimal germination time for A. theophrasti was late spring, as plants that germinated in this period achieved the maximum total mass, with the highest stem and reproductive allocation and the lowest leaf allocation, among plants of all germination treatments. Plants that germinated earlier in spring used a longer time for vegetative growth and did not outperform late-spring germinants, probably due to exposure to spring drought and response to competition. Delaying germination into summer led to a faster growth, increased leaf allocation, decreased stem allocation, advanced reproduction and shorter life cycle, but further delay of germination into late summer led to insufficient reproduction and incomplete life cycle due to extremely short growth period. Results suggested plants that germinated within the optimal period can maximize their growth potential in relatively favorable conditions. In spite of conspicuous disadvantages, plants with advanced and delayed germinated were still able to use different strategies to better adapt to subsequent environments, via plasticity in a number of allocation and morphological traits. Root plasticity may play a predominant or fundamental role in plant response to environments, or it is crucial to maintain root allocation stable, while stem or leaf allocation can often be sacrificed depending on specific situations.