Effect of three weeds on the growth and mycorrhizal infection of black walnut seedlings

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Abstract
The effect of unincorporated and incorporated litter and extracts of broom-sedge, fescue, and blackberry on the mycorrhizal development and growth of black walnut seedlings was investigated in two greenhouse experiments. Seedling growth varied with method of litter application. Only fescue extract decreased growth in the extract experiment, but unincorporated and incorporated broom-sedge litter significantly (P ≤ 0.05) reduced seedling total dry weight below that of mycorrhizal control seedlings. The total dry weight of seedlings in incorporated fescue litter was reduced by 47%. The number of mycorrhizal infected root segments on seedlings grown in unincorporated litter was more than twice the number of infected roots on seedlings grown in incorporated litters. Significantly fewer mycorrhizal roots were found on seedlings grown with fescue and broom-sedge litters than on mycorrhizal control seedlings. On the average, incorporation of litter increased the percentage of leaf phosphorus, but the shoot absorption of phosphorus was considerably less for seedlings grown in incorporated fescue litter compared with unincorporated fescue litter. Seedlings grown in fescue extract had 33% less phosphorus than control seedlings. Except for possible interference with mycorrhizal development when litter was incorporated, there was no evidence to suggest that blackberry litter contains substances that are allelopathic to black walnut.