Stable isotope signatures of pelotons and rhizomorphs reveal nutritional plasticity in Cremastra appendiculata (Orchidaceae).
- 1Department of Biology, Graduate School of Science, Kobe University, Kobe, 657-8501, Hyogo, Japan. [email protected].
- 2Institute for Advanced Research, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 657-8501, Hyogo, Japan. [email protected].
- 3Department of Biology, Graduate School of Science, Kobe University, Kobe, 657-8501, Hyogo, Japan.
Abstract
Many photosynthetic orchids combine photosynthesis with fungal carbon acquisition, yet the isotopic relationships between orchids and their fungal partners remain poorly resolved. Direct stable isotope analysis of pelotons and extraradical fungal tissues can refine fungal baselines and clarify nutritional dynamics in orchid mycorrhizas. We investigated Cremastra appendiculata, a photosynthetic orchid with contrasting mycorrhizal states, by comparing fungal communities between individuals with and without coralloid rhizomes and analyzing the δ¹³C and δ¹⁵N values of leaves, protocorms, coralloid rhizomes, pelotons, Psathyrellaceae rhizomorphs, dead wood, and autotrophic reference plants. Psathyrellaceae-associated individuals were strongly enriched in ¹³C relative to autotrophic reference plants, indicating substantial acquisition of fungal carbon, whereas rhizoctonia-associated individuals exhibited little ¹³C enrichment and appeared predominantly autotrophic. Leaf δ¹⁵N values exceeded those of the associated fungal tissues in both states, suggesting plant-mediated ¹⁵N enrichment during nitrogen assimilation and allocation to leaves. Coralloid rhizome pelotons did not differ detectably in δ¹³C or δ¹⁵N between digestion stages. Pelotons resembled extraradical Psathyrellaceae rhizomorphs in δ¹⁵N but had higher δ¹³C values, indicating tissue-specific carbon isotope baselines. Psathyrellaceae tissues were less ¹³C enriched than fungal tissues reported from fully mycoheterotrophic orchids associated with wood-decaying fungi. These results support contrasting nutritional states in C. appendiculata: a predominantly autotrophic, rhizoctonia-associated state and a more fungus-dependent, Psathyrellaceae-associated state. The fungal isotope pattern raises the possibility that bidirectional carbon transfer persists even in the latter state. Determining whether the orchid transfers carbon to its fungal partners requires controlled culture or tracer experiments.
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BibTeX
@article{suetsugu2026stable,
title = {{Stable isotope signatures of pelotons and rhizomorphs reveal nutritional plasticity in Cremastra appendiculata (Orchidaceae).}},
author = {Kenji Suetsugu and Hidehito Okada and Akihiro Nishimura},
journal = {Mycorrhiza},
year = {2026},
month = oct,
doi = {10.1007/s00572-026-01315-x},
url = {https://europepmc.org/article/MED/42836896},
note = {CC BY},
}
RIS
TY - JOUR
TI - Stable isotope signatures of pelotons and rhizomorphs reveal nutritional plasticity in Cremastra appendiculata (Orchidaceae).
AU - Kenji Suetsugu
AU - Hidehito Okada
AU - Akihiro Nishimura
PY - 2026
DA - 2026/10/06
JO - Mycorrhiza
DO - 10.1007/s00572-026-01315-x
UR - https://europepmc.org/article/MED/42836896
AB - Many photosynthetic orchids combine photosynthesis with fungal carbon acquisition, yet the isotopic relationships between orchids and their fungal partners remain poorly resolved. Direct stable isotope analysis of pelotons and extraradical fungal tissues can refine fungal baselines and clarify nutritional dynamics in orchid mycorrhizas. We investigated Cremastra appendiculata, a photosynthetic orchid with contrasting mycorrhizal states, by comparing fungal communities between individuals with and without coralloid rhizomes and analyzing the δ¹³C and δ¹⁵N values of leaves, protocorms, coralloid rhizomes, pelotons, Psathyrellaceae rhizomorphs, dead wood, and autotrophic reference plants. Psathyrellaceae-associated individuals were strongly enriched in ¹³C relative to autotrophic reference plants, indicating substantial acquisition of fungal carbon, whereas rhizoctonia-associated individuals exhibited little ¹³C enrichment and appeared predominantly autotrophic. Leaf δ¹⁵N values exceeded those of the associated fungal tissues in both states, suggesting plant-mediated ¹⁵N enrichment during nitrogen assimilation and allocation to leaves. Coralloid rhizome pelotons did not differ detectably in δ¹³C or δ¹⁵N between digestion stages. Pelotons resembled extraradical Psathyrellaceae rhizomorphs in δ¹⁵N but had higher δ¹³C values, indicating tissue-specific carbon isotope baselines. Psathyrellaceae tissues were less ¹³C enriched than fungal tissues reported from fully mycoheterotrophic orchids associated with wood-decaying fungi. These results support contrasting nutritional states in C. appendiculata: a predominantly autotrophic, rhizoctonia-associated state and a more fungus-dependent, Psathyrellaceae-associated state. The fungal isotope pattern raises the possibility that bidirectional carbon transfer persists even in the latter state. Determining whether the orchid transfers carbon to its fungal partners requires controlled culture or tracer experiments.
SN - 0940-6360
SN - 1432-1890
ER -