Acquisition of N By Plants from 15N-Labeled Root and Leaf Litter

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Organic soils, particularly in northern climates, are often inhabited by ericoid mycorrhizal shrubs. Previous work, generally conducted under axenic conditions and/or with simple forms of organic N, suggests ericoid mycorrhizal fungi may confer a competitive advantage to their hosts through N uptake from organic sources. We hypothesized that ericoid mycorrhizal shrubs would acquire more N from 15N-enriched litter (pine and huckleberry roots and foliage) than would ectomycorrhizal pines. Plants were grown alone and in pairs in a pot experiment with 15N-enriched litter and N uptake was assessed after 1.5, 5, and 12 months. Chemical properties of the 15N-litter differed by species and by plant part. Lower concentrations of polyphenols and tannins, lower C/N ratio, and higher ADF-lignin/N ratio were characteristic of pine relative to huckleberry litter and of root relative to foliage litter.

When grown alone, pines acquired more N from root litter than from foliage litter and both species recovered more N from pine litter than from huckleberry litter. Across all treatments, the greatest quantity of litter N was recovered by pines from pine root litter. When N recovery was compared between pines and huckleberries, it was evident that this difference increased in favor of ericoid mycorrhizal huckleberries as litter tannin concentration increased. Tannin concentration was lowest in pine root litter and highest in huckleberry foliage litter. Thus, when planted singly, each species had the greatest advantage in litter N recovery when grown in its own litter.

When pines and huckleberries were planted in pairs, pines in interspecific pairs grew less and acquired less litter N than did pines in conspecific pairs. This effect was not observed in huckleberries and was independent of differences in litter quality, suggesting that, in addition to the production of recalcitrant litter, huckleberries possess other mechanisms to suppress competition by pines in organic soils.

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Presented at the International Annual Meeting of the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America on October 23, 2017 in Tampa, FL