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"From Plant Soil 57 (1980), 363-374. Allelopathic potential of ground cover species on Pinus resinosa seedlings. Norby, R. J., and Kozlowski, T. T. Table 3, with kind permission from Kluwer Academic Publishers. ''Mean of 10 seedlings ± standard error. 'Significantly different from control at p < 0.05. ^Significantly different from control at p < 0.01. 'Significantly different from control at p < 0.001.

"From Plant Soil 57 (1980), 363-374. Allelopathic potential of ground cover species on Pinus resinosa seedlings. Norby, R. J., and Kozlowski, T. T. Table 3, with kind permission from Kluwer Academic Publishers. ''Mean of 10 seedlings ± standard error. 'Significantly different from control at p < 0.05. ^Significantly different from control at p < 0.01. 'Significantly different from control at p < 0.001.

tion and allelopathy arrested growth of Scotch pine seedlings. Mahall and Callaway (1992) reduced the allelopathic influence of roots of creosote bush on adjacent plants by absorbing toxins in the soil with activated carbon.

Although many laboratory studies showed allelopathic effects of plant extracts, Lerner and Evenari (1961) advised caution in extrapolating the results of such experiments to field situations. Some studies used leaching or extraction procedures that gave little insight into natural release of allelochemicals (May and Ash, 1990). Hence, concentrations of allelopathic chemicals in many studies were higher than those to which plants in the field are subjected. Accumulation of allelochems in the field is modified by soil moisture and soil type. Furthermore, the field allelochems often are destroyed by soil microflora. Inderjit and Dakshini (1995) concluded that many laboratory assays of allelopathy had little relevance to field situations. This discrepancy typically results because of differences between laboratory tests and natural conditions, lack of standardized experimental methods, and lack of adequate controls.

Failure of regeneration of black cherry trees in old fields and forests was attributed to allelopathic interference by hay-scented fern (Horsley, 1977a,b). However, when black cherry seedlings were grown in soils from areas with and without hay-scented fern, height growth of black cherry seedlings did not differ, indicating that allelopathic chemicals from hay-scented fern were not accumulating in the field. Often the sites on which allelopathy is indicated are poorly drained, which may prevent leaching away or decomposition of allelochems.

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