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Shoot Competition and Root Competition

J. Bastow Wilson
Journal of Applied Ecology
Vol. 25, No. 1 (Apr., 1988), pp. 279-296
DOI: 10.2307/2403626
Stable URL: http://www.jstor.org/stable/2403626
Page Count: 18
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Shoot Competition and Root Competition
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Abstract

(1) The effects of shoot and root competition in twenty-three studies including additive and replacement techniques, radial and linear layouts, a variety of methods of partitioning and a variety of species are reviewed. (2) The effects of competition were measured by: (i) the competitive balance (relative competitive ability) of the components of the mixture using the competitive balance index, Cb, (ii) the intensity of competition (as determined by plant size) using the competitive intensity index, C1, (iii) the efficiency of resource use by the mixture using the relative yield total (RYT), relative yield of the mixture (RYM) and overyield. (3) Root competition usually affected the balance between components more than shoot competition. Similarly, root competition was usually more intense than shoot competition. However, in crop-weed experiments, shoot competition was often more intense than root competition; crops usually had a greater competitive ability than weeds. (4) The only firm evidence suggests that the relative importance of root competition increases with time, though in some situations the reverse may be true. (5) Increased yield of a mixture can indicate niche separation, which is of potential agricultural significance as a means of obtaining higher yields than with monocultures. Increased yield of mixtures tended to occur in experiments that allowed different species to root at different depths, and root interaction was usually the more important cause. (6) Although positive interaction between shoot and root competition has often been considered a basic feature of competition, such interactions occurred rarely; in the case of intensity of competition the interaction was usually negative. (7) There is little evidence to justify the common assumption that adding environmental resources reduces competitive effects; competitive imbalance was often greater at higher resource levels.

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