© 1993 Heron Publishing—Victoria, Canada
Growth and nutrition of nonmycorrhizal and mycorrhizal pitch pine (Pinus rigida) seedlings under phosphorus limitation
Jonathan R. Cumming
Department of Botany, University of Vermont, Burlington, VT 05405-0086, USA / Received November 11, 1992
Summary
The association of ectomycorrhizal fungi with tree roots enhances the acquisition of phosphorus (P) from the soil. In addition
to increasing the uptake of H2PO4– (Pi), mycorrhizal fungi may increase the spectrum of P sources utilized by tree roots by mediating the dissolution of insoluble
metallophosphate salts or the hydrolysis of organic P compounds. To investigate the role of ectomycorrhizal fungi in enhancing
P acquisition by tree roots, pitch pine (Pinus rigida Mill.) seedlings were grown in sand culture with or without the ectomycorrhizal symbiont Pisolithus tinctorius Coker and Couch under various conditions of P limitation. Compared with nonmycorrhizal seedlings, seedlings inoculated with
P. tinctorius exhibited a greater capacity to function under P limitation as evidenced by superior growth and the
maintenance of normal foliar ion composition at low Pi concentrations. Nonmycorrhizal seedlings subjected to P-limiting conditions exhibited depressed K and P and elevated Na concentrations
in foliage. The association of P. tinctorius with pitch pine seedling roots maintained foliar K concentrations and prevented the accumulation of Na under P limitation.
Nonmycorrhizal seedlings were unable to obtain P from either solid AlPO4 or inositol hexaphosphate (IHP), whereas seedlings inoculated with P. tinctorius
utilized AlPO4, but not IHP as a P source. Root surface acid phosphatase (APase) activity was depressed in roots infected with the mycorrhizal
symbiont and was negatively correlated with seedling growth on all P sources. Root APase activity was negatively correlated
with foliar P concentrations in seedlings grown on Pi, but was not correlated with foliar P concentrations in seedlings cultured with AlPO4 or IHP.
Keywords:
acid phosphatase, ectomycorrhizae, nutrition, phosphorus, Pisolithus tinctorius.
