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Ann Bot. 2017 Sep 1;120(3):361-371. doi: 10.1093/aob/mcx054.

Mixotrophy in Pyroleae (Ericaceae) from Estonian boreal forests does not vary with light or tissue age.

Author information

1
Institut de Systématique, Évolution, Biodiversité (ISYEB), UMR 7205 CNRS MNHN UPMC EPHE, Muséum national d'Histoire naturelle, Sorbonne Universités, 57 rue Cuvier, CP39, 75005 Paris, France.
2
Master BioSciences, Département de Biologie, École Normale Supérieure de Lyon, Université de Lyon, UCB Lyon1, 46 Allée d'Italie, Lyon, France.
3
Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Street Kreutzwaldi 5, 51014, Tartu, Estonia.
4
Institute of Forestry and Rural Engineering, Estonian University of Life Sciences, Street Kreutzwaldi 5, 51014 Tartu, Estonia.
5
Tartu Observatory, 61602 Tõravere, Tartu County, Estonia.
6
Agroécologie, AgroSupDijon, CNRS, INRA, Université de Bourgogne Franche-Comté, 21000 Dijon, France.
7
Department of Plant Taxonomy and Nature Conservation, University of Gdansk, ul. Wita Stwosza 59, 80-308 Gdańsk, Poland.

Abstract

Background and Aims:

In temperate forests, some green plants, namely pyroloids (Pyroleae, Ericaceae) and some orchids, independently evolved a mode of nutrition mixing photosynthates and carbon gained from their mycorrhizal fungi (mixotrophy). Fungal carbon is more enriched in 13C than photosynthates, allowing estimation of the proportion of carbon acquired heterotrophically from fungi in plant biomass. Based on 13C enrichment, mixotrophic orchids have previously been shown to increase shoot autotrophy level over the growth season and with environmental light availability. But little is known about the plasticity of use of photosynthetic versus fungal carbon in pyroloids.

Methods:

Plasticity of mixotrophy with leaf age or light level (estimated from canopy openness) was investigated in pyroloids from three Estonian boreal forests. Bulk leaf 13C enrichment of five pyroloid species was compared with that of control autotrophic plants along temporal series (over one growth season) and environmental light gradients (n=405 samples).

Key Results:

Mixotrophic 13C enrichment was detected at studied sites for Pyrola chlorantha and Orthilia secunda (except at one site for the latter), but not for Chimaphila umbellata, Pyrola rotundifolia and Moneses uniflora. Enrichment with 13C did not vary over the growth season or between leaves from current and previous years. Finally, although one co-occurring mixotrophic orchid showed 13C depletion with increasing light availability, as expected for mixotrophs, all pyroloids responded identically to autotrophic control plants along light gradients.

Conclusions:

A phylogenetic trend previously observed is further supported: mixotrophy is rarely supported by 13C enrichment in the Chimaphila + Moneses clade, whereas it is frequent in the Pyrola + Orthilia clade. Moreover, pyroloid mixotrophy does not respond plastically to ageing or to light level. This contrasts with the usual view of a convergent evolution with orchids, and casts doubt on the way pyroloids use the carbon gained from their mycorrhizal fungi, especially to replace photosynthetic carbon.

KEYWORDS:

13C; Chimaphila; Ericaceae; Moneses; N content; Orthilia; Pyrola; mixotrophy; mycoheterotrophy; orchids; response to light; stable isotopes

PMID:
28575199
PMCID:
PMC5591414
DOI:
10.1093/aob/mcx054
[Indexed for MEDLINE]
Free PMC Article

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