Response of plants to ectomycorrhizae in N-limited conditions: which factors determine its variation?
In the present work, the following hypotheses were tested: (1) the negative effects of mycorrhization over host plant productivity in N-limited conditions are due to N retention by the fungal partner and not due to excessive C drainage; (2) If mycorrhization results in decreased N uptake, the host plant decreases its C investment in fungal growth. The effects of mycorrhization over a wide range of combinations between N availability, N concentration in plant tissues, and degree of mycorrhizal colonization were studied in Pinus pinaster L. mycorrhizal with Pisolithus tinctorius. Several plant productivity parameters, the seedlings' N status, chl a fluorescence (JIP test), and mycorrhizal colonization were measured. N was always limiting. A gradient of mycorrhizal effects over the host plant's growth and vitality was successfully obtained. The mycorrhizal effects on plant growth and N uptake were very strongly and positively correlated, and no evidence was found of a C limitation to growth, confirming hypothesis 1. Indications were found that the plants continued to provide C to the fungus although the N supplied by it was increasingly lower, denying hypothesis 2. A new index, the mycorrhizal N demand-supply balance, was found to efficiently explain, and to have a curvilinear relation with, the variation in response to mycorrhization. The mycorrhizal effect on host plant growth was not related to a negative effect on its photosynthetic performance and, therefore, reflected changes in resource allocation between host plant and mycorrhizal fungus, not in plant vitality.
Corrêa
A
A
Centro de Ecologia e Biologia Vegetal-CEBV, Universidade de Lisboa, Faculdade de Ciências, Campo Grande, Edifício C4, Piso 1, 1749-016, Lisbon, Portugal. a.correa@iol.pt.
Strasser
R J
RJ
Laboratoire de Bioénergétique, Université de Genève, Chemin des Embrouchis 10, 1254, Jussy, Geneva, Switzerland.
Martins-Loução
M A
MA
Centro de Ecologia e Biologia Vegetal-CEBV, Universidade de Lisboa, Faculdade de Ciências, Campo Grande, Edifício C4, Piso 1, 1749-016, Lisbon, Portugal.
D001487:Basidiomycota / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D002244:Carbon / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D006790:Host-Parasite Interactions / Q000502:physiology*; D038821:Mycorrhizae / Q000254:growth & development / Q000502:physiology*; D009584:Nitrogen / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology; D028223:Pinus / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology* / Q000502:physiology*
D002734:Chlorophyll; D002244:Carbon; D009584:Nitrogen; D000077194:Chlorophyll A