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Challenging the tragedy of the commons in root competition: confounding effects of neighbour presence and substrate volume
Author(s) -
SEMCHENKO MARINA,
HUTCHINGS MICHAEL J.,
JOHN ELIZABETH A.
Publication year - 2007
Publication title -
journal of ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.452
H-Index - 181
eISSN - 1365-2745
pISSN - 0022-0477
DOI - 10.1111/j.1365-2745.2007.01210.x
Subject(s) - competition (biology) , tragedy of the commons , shoot , biology , substrate (aquarium) , volume (thermodynamics) , botany , agronomy , chemistry , commons , ecology , physics , quantum mechanics
Summary1 It 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. 2 Six 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. 3 We 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. 4 In the treatment with gravel, plants displayed reduced tillering and shoot growth per unit root mass, and an earlier switch to reproduction. 5 Pot 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. 6 We 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.