Challenging the tragedy of the commons in root competition: confounding effects of neighbour presence and substrate volume
Article first published online: 24 JAN 2007
© 2007 The Authors. Journal compilation © 2007 British Ecological Society
Journal of Ecology
Volume 95, Issue 2, pages 252–260, March 2007
How to Cite
SEMCHENKO, M., HUTCHINGS, M. J. and JOHN, E. A. (2007), Challenging the tragedy of the commons in root competition: confounding effects of neighbour presence and substrate volume. Journal of Ecology, 95: 252–260. doi: 10.1111/j.1365-2745.2007.01210.x
- Issue published online: 12 FEB 2007
- Article first published online: 24 JAN 2007
- Received 25 June 2006 revision accepted 6 November 2006Handling Editor: David Gibson
- Avena sativa;
- activated carbon;
- pot partitions;
- root exudates;
- root interactions;
- self/non-self discrimination;
- substrate volume;
- tragedy of the commons
- 1It has been claimed that, compared with plants grown without competition, plants competing for a common pool of soil-based resources overproduce roots at the expense of reproduction (known as the tragedy of the commons). However, experiments on this phenomenon have manipulated not only the presence/absence of neighbours, but also substrate volume. Restricted substrate volume can itself affect plant growth, possibly through chemical self-inhibition of root growth. We conducted an experiment with oats (Avena sativa) to examine whether the experimental design used in previous studies on the tragedy of the commons in root competition might have confounded the effects of detection of neighbours and substrate volume.
- 2Six treatments combined two factors, namely the presence or absence of activated carbon, and either the presence of a plastic or a mesh partition, or the absence of a partition, between two plants in a pot. Activated carbon was used to adsorb root exudates and reduce their potential effects on root growth. In a seventh treatment, plants were grown alone in pots with half the substrate volume replaced by gravel, to fragment the distribution of available resources.
- 3We observed no tragedy of the commons in a comparison of the performance of plants grown with and without partitions; plants performed equally well in the presence and absence of root competition.
- 4In the treatment with gravel, plants displayed reduced tillering and shoot growth per unit root mass, and an earlier switch to reproduction.
- 5Pot partitioning was associated with inhibition of root growth that was mediated by root exudates. When activated carbon was present, plants in partitioned pots performed better than plants growing with a root competitor.
- 6We conclude that two processes could determine plant growth in the experimental design used in studies of the tragedy of the commons: (i) greater root self-inhibition in the more limited space of partitioned pots, and (ii) inefficient root placement in larger substrate volumes in unpartitioned pots that are shared with roots of a competitor. These findings provide a new challenge for experimental designs attempting to demonstrate the role of self/non-self discrimination in root competition.