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Summary Ectomycorrhizal symbiosis is essential for the nutrition of most temperate forest trees and helps regulate the movement of carbon (C) and nitrogen (N) through forested ecosystems. The factors governing the exchange of plant C for fungal N, however, remain obscure.Because competition and soil resources may influence ectomycorrhizal resource movement, we performed a 10‐month split‐root microcosm study usingPinus muricataseedlings withThelephora terrestris,Suillus pungens, or no ectomycorrhizal fungus, under two N concentrations in artificial soil. Fungi competed directly with roots and indirectly with each other. We used stable isotope enrichment to track plant photosynthate and fungal N.ForT. terrestris, plants received N commensurate with the C given to their fungal partners.Thelephora terrestriswas a superior mutualist under high‐N conditions. ForS. pungens, plant C and fungal N exchange were not coupled. However, in low‐N conditions, plants preferentially allocated C toS. pungensrather thanT. terrestris.Our results suggest that ectomycorrhizal resource transfer depends on competitive and nutritional context. Plants can exchange C for fungal N, but coupling of these resources can depend on the fungal species and soil N. Understanding the diversity of fungal strategies, and how they change with environmental context, reveals mechanisms driving this important symbiosis.
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Dirt cheap: an experimental test of controls on resource exchange in an ectomycorrhizal symbiosis
Summary To distinguish among hypotheses on the importance of resource‐exchange ratios in outcomes of mutualisms, we measured resource (carbon (C), nitrogen (N), and phosphorus (P)) transfers and their ratios, betweenPinus taedaseedlings and two ectomycorrhizal (EM) fungal species,Rhizopogon roseolusandPisolithus arhizusin a laboratory experiment.We evaluated how ambient light affected those resource fluxes and ratios over three time periods (10, 20, and 30 wk) and the consequences for plant and fungal biomass accrual, in environmental chambers.Our results suggest that light availability is an important factor driving absolute fluxes of N, P, and C, but not exchange ratios, although its effects vary among EM fungal species. Declines in N : C and P : C exchange ratios over time, as soil nutrient availability likely declined, were consistent with predictions of biological market models. Absolute transfer of P was an important predictor of both plant and fungal biomass, consistent with the excess resource‐exchange hypothesis, and N transfer to plants was positively associated with fungal biomass.Altogether, light effects on resource fluxes indicated mixed support for various theoretical frameworks, while results on biomass accrual better supported the excess resource‐exchange hypothesis, although among‐species variability is in need of further characterization.
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- Award ID(s):
- 1119865
- PAR ID:
- 10390367
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 237
- Issue:
- 3
- ISSN:
- 0028-646X
- Format(s):
- Medium: X Size: p. 987-998
- Size(s):
- p. 987-998
- Sponsoring Org:
- National Science Foundation
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