Contemporary adaptive divergence of plant competitive traits in urban and rural populations and its implication for weed management

1. Competition among neighboring plants plays essential roles in growth,
reproduction, population dynamics, and community assembly, but how
competition drives local adaptation and the traits underlying the
adaptation remain unclear. Here, we focused on populations of the
aggressive weed Digitaria ciliaris from urban and rural habitats as low-
and high-competition environments for light resources and examined how
competitive interaction drove contemporary adaptive divergence of
competitive traits. 2. To examine local adaptation to different
competitive environments in D. ciliaris and the specific traits that have
been selected for, we compared growth rate and competitive traits in
plants from farmland and urban populations between high- and
low-competition treatments. Furthermore, we conducted a field tillage
experiment with drone (UAV) monitoring to examine the possibility that
trait evolution in farmland habitats might influence weed management
practices in crop fields. 3. Plants from farmland populations had higher
growth rates than plants from urban populations in high-competition
treatments, and vice versa in low-competition treatments. Among
populations, those with larger height/width ratios (farmland populations)
were more tolerant of aboveground competition in high-competition
treatments, but among individuals, those with larger ratios had lower
growth rates in low-competition treatments. More plants from farmland
populations, which had thicker stems (and larger height/width ratios),
survived after experimental tillage than plants from urban habitats with
thinner stems. 4. Synthesis. Our study empirically demonstrated adaptive
divergence in competitive traits in aboveground competitors and its
underlying traits. Moreover, contemporary adaptive divergence between
urban and rural plant populations has practical implications for weed
control. The urban–rural model system can thus contribute to both basic
and applied research in plant evolutionary ecology. Further research is
required to understand adaptive divergence in plants between urban and
rural environments, and the traits underlying the adaptation, not only
aboveground, but also belowground.