Competition is a key feature that structures the composition of plant communities. A growing body of evidence is showing that the presence of neighbours, especially belowground neighbours, induces varied morphological responses in plants. However, in many species, it is not known whether neighbour identity also influences plant morphological responses such as biomass allocation patterns. To assess plant response to above- and belowground neighbour presence and identity, we conducted a greenhouse experiment consisting of conspecific (pea; Pisum sativum L.) and heterospecific (oat; Avena sativa L.) neighbours growing with a P. sativum focal plant. Four interaction regimes were constructed including shoot, root, or ‘full’ interaction (root & shoot) treatments, as well as a control with no interactions permitted. Our results showed that pea plants responded negatively to the presence of neighbours, and in particular, the presence of belowground neighbours. Treatments where belowground interactions were permitted (full and root interactions) had lower root and shoot mass fractions (R:S ratios) than where shoot interactions were permitted. Shoot and root allocation and R:S ratios of focal pea plants were not affected by neighbour identity, suggesting that neighbour presence, but not identity, influenced allocation patterns. The impact on P. sativum of a neighbouring competitor was more prominent than neighbour identity, showing that some plants may not discriminate between the identity of neighbours even though they are capable of responding to their presence.

The inclusion of competitive crop cultivars in crop rotations is an important integrated weed management (IWM) tool. However, competitiveness is often not considered a priority for breeding or cultivar selection by growers. Field pea (Pisum sativumL.) is often considered a poor competitor with weeds, but it is not known whether competitiveness varies among semileafless cultivars. The objectives of this study were to determine if semileafless field pea cultivars vary in their ability to compete and/or withstand competition, as well as to identify aboveground trait(s) that may be associated with increased competitive ability. Field experiments were conducted in 2012 and 2013 at three locations in western Canada. Fourteen semileafless field pea cultivars were included in the study representing four different market classes. Cultivars were grown either in the presence or absence of model weeds (wheat and canola), and competitive ability of the cultivars was determined based on their ability to withstand competition (AWC) and their ability to compete (AC). Crop yield, weed biomass and weed fecundity varied among sites but not years. Cultivars exhibited inconsistent differences in competitive ability, although cv. Reward consistently exhibited the lowest AC and AWC. None of the traits measured in this study correlated highly with competitive ability. However, the highest-yielding cultivars generally were those that had the highest AC, whereas cultivars that ranked highest for AWC were associated with lower weed fecundity. Ranking the competitive ability of field pea cultivars could be an important IWM tool for growers and agronomists.

No abstract