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Differential effects of mineral and organic N sources, and of ectomycorrhizal infection by Hebeloma cylindrosporum , on growth and N utilization in Pinus pinaster
Author(s) -
Plassard C.,
Bonafos B.,
Touraine B.
Publication year - 2000
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1046/j.1365-3040.2000.00630.x
Subject(s) - mycorrhiza , biology , botany , pinus pinaster , ectomycorrhiza , nutrient , horticulture , symbiosis , ecology , bacteria , genetics
The effect of ectomycorrhizal association of Pinus pinaster with Hebeloma cylindrosporum was investigated in relation to the nitrogen source supplied as mineral (NH 4 + or NO 3 − ) or organic N ( L ‐glutamate) and at 5 mol m − 3 . Plants were grown for 14 and 16 weeks with mineral and organic N, respectively, and samples were collected during the last 6 weeks of culture. Total fungal biomass was estimated using glucosamine amount and its viability was assessed using the glucosamine to ergosterol ratio. Non‐mycorrhizal plants grew better with NH 4 + than with NO 3 − and grew very slowly when supplied with L ‐glutamate. The presence of the fungus decreased the growth of the host plant with mineral N whereas it increased it with L ‐glutamate. Whatever the N source, most of the living fungal biomass was associated with the roots, whereas the main part of the total biomass was assayed outside the root. The form of mineral N did not significantly affect N accumulation rates over the 42 d in control plants. In mycorrhizal plants grown on either N source, the fungal tissues developing outside of the root were always the main N sink. The ectomycorrhizal association did not change 15 NH 4 + uptake rate by roots, suggesting that the growth decrease of the host‐plant was related to the carbon cost for fungal growth and N assimilation rather than to a direct effect on NH 4 + acquisition. In contrast, in NO 3 − ‐grown plants, in addition to draining carbon for NO 3 − reduction the fungus competed with the root for NO 3 − uptake. With NH 4 + or NO 3 − feeding, although mycorrhizal association improved N accumulation in shoots, we concluded that it was unlikely that the fungus had supplied the plant with N. In L ‐glutamate‐grown plants, the presence of the fungus increased the proportion of glutamine in the xylem sap and improved both N nutrition and the growth rate of the host plant.