Epsilon Archive for Student Projects

Abstract

Echinochloa crus-galli (L.) P. Beauv. (barnyardgrass) ranks among the most significant agricultural weeds globally due to its high competitiveness, broad ecological range, and high phenotypic plasticity. Despite becoming an increasingly problematic weed in Northern European cropping systems, it remains unclear how populations originating from northern and southern European environments differ when exposed to the same environmental conditions.

This thesis quantified developmental, vegetative, and generative variation among 26 European populations of E. crus-galli and addressed whether populations from boreal and nemoral environments differ from those originating from continental and Mediterranean environments in phenology, biomass allocation, functional vegetative and generative traits, and trait variation when grown under the same environmental conditions. Populations from boreal/nemoral (BOR/NEM) and continental/Mediterranean (CON/MED) regions were grown in a common garden experiment simulating a 22-week growing season in southern Sweden. The thesis assessed phenological development throughout the growing season, including key developmental stages; biomass allocation to vegetative organs (leaves, stems, and roots); specific leaf area measured using ImageJ, plant height, and seed production and mass as part of the leaf – height – seed (LHS) strategy; population positioning along the competitive – stress-tolerant – ruderal (CSR) strategy; and the proportions of trait variation within and between populations and regions.

At inflorescence emergence, BOR/NEM populations generally required 387 – 590 growing degree days (GDD), compared with 529 – 736 GDD for CON/MED populations. At flowering, the ranges were 416 – 630 and 563 – 767 GDD, respectively, indicating earlier generative development in BOR/NEM populations under Swedish conditions. Biomass allocation patterns also differed between regions; CON/MED populations generally produced more aboveground biomass, whereas some BOR/NEM populations allocated biomass more evenly between aboveground and belowground organs. Principal component analysis (PCA) of leaf – height – seed (LHS) strategy explained 90.9 % of the total variation and revealed three distinct functional groupings among populations, representing alternative competitiveness pathways through plant height, resource uptake, or reproductive traits. All populations had 80 – 90 % competitive scores in the CSR classification, although BOR/NEM populations tended to have a larger ruderal component. Variance partitioning demonstrated variation both within and among populations for vegetative and generative traits, as well as between and within regions.

I conclude that European populations of E. crus-galli differ in how they express traits associated with competition and reproduction under the common garden experiment. BOR/NEM populations completed generative development with less accumulated GDD, whereas CON/MED populations became taller and invested more in aboveground growth. These patterns suggest that adaptation to northern European environments may involve earlier reproduction rather than increased vegetative growth. Variation within populations may also mean that individuals from the same population respond differently to environmental conditions and weed management practices.

The results therefore indicate that E. crus-galli does not rely on a single combination of traits associated with weediness. Instead, populations achieved competitive success through different combinations of functional traits associated with resource uptake, light competition, root development, and reproduction. The LHS strategy analysis revealed multiple pathways to competitiveness within the species, indicating that populations with different environmental histories may express distinct ecological strategies despite belonging to the same species.