Direct and indirect influences of arbuscular mycorrhizal fungi on phosphorus uptake by two root hemiparasitic Pedicularis species: do the fungal partners matter at low colonization levels?
OBJECTIVE
Because most parasitic plants do not form mycorrhizal associations, the nutritional roles of arbuscular mycorrhizal (AM) fungi in them have hardly been tested. Some facultative root hemiparasitic Pedicularis species form AM associations and hence are ideal for testing both direct and indirect effects of AM fungi on their nutrient acquisition. The aim of this study was to test the influence of AM inoculation on phosphorus (P) uptake by Pedicularis rex and P. tricolor.


METHODS
(32)P labelling was used in compartmented pots to assess the contribution of the AM pathway and the influence of AM inoculation on P uptake from a host plant into the root hemiparasites. Laboratory isolates of fungal species (Glomus mosseae and G. intraradices) and the host species (Hordeum vulgare 'Fleet') to which the two Pedicularis species showed obvious responses in haustorium formation and growth in previous studies were used.


RESULTS
The AM colonization of both Pedicularis spp. was low (<15 % root length) and only a very small proportion of total plant P (<1 %) was delivered from the soil via the AM fungus. In a separate experiment, inoculation with AM fungi strongly interfered with P acquisition by both Pedicularis species from their host barley, almost certainly because the numbers of haustoria formed by the parasite were significantly reduced in AM plants.


CONCLUSIONS
Roles of AM fungi in nutrient acquisition by root parasitic plants were quantitatively demonstrated for the first time. Evidence was obtained for a novel mechanism of preventing root parasitic plants from overexploiting host resources through AM fungal-induced suppression of the absorptive structures in the parasites.
Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, PR China.
Ai-Rong
AR
Li
Kai-Yun
KY
Guan
Rebecca
R
Stonor
Sally E
SE
Smith
F Andrew
FA
Smith
D018533:Biomass; D055137:Glomeromycota / Q000502:physiology*; D001467:Hordeum / Q000469:parasitology*; D038821:Mycorrhizae / Q000502:physiology*; D032262:Pedicularis / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology*; D010758:Phosphorus / Q000378:metabolism*; D010761:Phosphorus Radioisotopes / Q000032:analysis; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology; D018520:Plant Shoots / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology; D013559:Symbiosis
D010761:Phosphorus Radioisotopes; D010758:Phosphorus
Arbuscular mycorrhizal fungi; Glomus; Hordeum vulgare; Orobanchaceae; P. tricolor; Pedicularis rex; barley; phosphorus uptake; root hemiparasitic plant