The separation of above- and below-ground competition in plants - A review and critique of methodology

The relative merits of different methods for separating root and shoot competition in plants are reviewed. The 'Divided Pot' technique involves vertical partitions that divide above- and below-ground competition within pots. This design usually creates unrealistic competition for light by using artificial barriers around pot perimeters to contain above-ground growth and by using a constant orientation of incident light from directly above. The 'Row' technique involves parallel rows of plants that are separated by vertical partitions above- and below-ground. Although, this design may be well suited to some agricultural applications, its value for field studies of wild plants is limited. The Divided Pot and Row techniques have been associated often with the replacement series design, which has a number of limitations. The 'Target' technique has always been associated with an additive planting design as it involves surrounding a plant of interest (the 'target') with other plants (the 'neighbours') while including above- and below-ground partitions to prevent root and shoot competition. Most studies using this technique have not provided adequate control for apparatus effects, yet this method appears to have the most potential for application in ecological studies, especially in the field. A standard protocol for the target technique is proposed allowing greater control over potential apparatus effects than in previous studies and allowing assessment of the interaction between root competition and shoot competition.