Short‐term phosphorus uptake rates in mycorrhizal and non‐mycorrhizal roots of intact Pinus sylvestris seedlings

Abstract

Short-term phosphate uptake rates were measured on intact ectomycorrhizal and non-mycorrhizal Pinus sylvestris seedlings using a new, non-destructive method. Uptake was quantified in semihydroponics from the depletion of P i in a nutrient solution percolating through plant containers. Plants were grown for 1 or 2 months after inoculation at a low relative nutrient addition rate of 3 % d −" and under P limitation. Four ectomycorrhizal fungi were studied : Paxillus involutus, Suillus luteus, Suillus bovinus and Thelephora terrestris. The P i -uptake capacity of mycorrhizal plants increased sharply in the month after inoculation. The increase was dependent on the development of the mycobionts. A positive correlation was found between the P i -uptake rates of the seedlings and the active fungal biomass in the substrate as measured by the ergosterol assay. The highest P i -uptake rates were found in seedlings associated with fungi producing abundant external mycelia. At an external P i concentration of 10 µM, mycorrhizal seedlings reached uptake rates that were 2.5 (T. terrestris) to 8.7 (P. involutus) times higher than those of non-mycorrhizal plants. The increased uptake rates did not result in an increased transfer of nutrients to the plant tissues. Nutrient depletion was ultimately similar between mycorrhizal and non-mycorrhizal plants in the semihydroponic system. Net P i absorption followed Michaelis-Menten kinetics : uptake rates declined with decreasing P i concentrations in the nutrient solution. This reduction was most pronounced in nonmycorrhizal seedlings and plants colonized by T. terrestris. The results confirm that there is considerable heterogeneity in affinity for P i uptake among the different mycobionts. It is concluded that the external mycelia of ectomycorrhizal fungi strongly influence the P i -uptake capacity of the pine seedlings, and that some mycobionts are well equipped to compete with other soil microorganisms for P i present at low concentrations in soil solution.

Changes in nitrogen level and mycorrhizal structure of Scots pine seedlings inoculated with Thelephora terrestris

“…Nitrogen nutrition research has always been subjected to conflicted results that may be caused by differences in the nitrogen nutrition of mycorrhizal fungal species and their isolates (Termorshuizen and Ket, 1991). Some authors found greater below-biomass of plants at low N availability (Colpaert et al, 1999;Raich and Nadelhoffer, 1989) but even if the below-biomass was greater there was no significant differences in the above-ground biomass (Hobbie and Colpaert, 2003).…”

Nitrogen availability and mycorrhizal colonization influence water use efficiency and carbon isotope patterns inPinus sylvestris

“…Ten nonmycorrhizal seedlings followed the same procedure in the absence of fungal inoculum and five plants were immediately harvested to determine %C, δ 13 C and C amounts at inoculation. Plants were transferred 3 d later to 70-cm 3 containers filled with 4.6 g acid-washed, sieved perlite (2 -4 mm particles) (Colpaert et al, 1999). Perlite has a low nutrient buffering capacity so plants are growing in a semihydroponic environment where nutrient addition and nutrient uptake in the plants are equivalent.…”

“…Subsequently, containers were centrifuged at 135 g for 30 s in order to remove most of the solution retained in the perlite. Roots and perlite were pulled out of the containers and roots separated from the perlite (Colpaert et al, 1999). Fine roots were detached from coarse roots, mycorrhizas being included in the former fraction.…”

“…Subsamples of perlite were frozen in liquid N to determine the concentration of ergosterol, a fungal biomarker. Ergosterol was analysed by HPLC and results were converted to fungal biomass using conversion factors of 3.0 and 5.9 mg ergosterol g −1 biomass for T. terrestris and S. luteus, respectively (Colpaert et al, 1999). Dry weights of foliage, stems, and roots were determined.…”

Survival and growth of nursery inoculated Fraxinus uhdei in acrisol gullies

“…These fungi play a key role in the establishment and development of most plants (Colpaert, Tichele, Assche and Laere, 1999;Allen, Swenson, Querejeta, Egerton-Warburton and Treseder, 2003). Among the multiple benefits attributed to mycorrhization, its effect on plant development stands out, since there is widespread proof that mycorrhizas improve plant growth by increasing the absorption surface of the root system (Smith and Read, 1997), selectively absorbing and storing certain nutrients (Colpaert et. al., 1999), solubilizing certain chemicals and making some chemical elements that are normally insoluble, in particular phosphorus, available for the plant (Casarin, Plassard, Hinsinger and Arvieu, 2004;Liu, Loganathan, Hedley and Skinner, 2004).…”