Fig. 2.

Relationship between the Ellenberg light availability index and stable isotope enrichment factors ε ¹³C for 41 Paris-morphotype arbuscular mycorrhizal (AM) plant species. Significance of ¹³C enrichment tested towards co-occurring Arum-type AM species is highlighted by species labels (see Supplementary data Table S3). (A) Pteridophytes (horsetails and ferns). A negative correlation between light and fungal carbon gain [black solid line, t(34) = 12.8, r²_adj = 0.7, P = 0.016, dotted line: 95 % confidence intervals]. (B) Seed plant species. No clear correlation. The coloured solid lines illustrate a regression among seed plant species significantly ¹³C enriched separated by forest habitats [dark khaki-coloured solid line and symbols; t(73) = 0.1, r²_adj = 0.0, P = 0.741] and open lands [light khaki-coloured solid line and symbols; t(84) = 0.1, r²_adj = 0.0, P = 0.729] (dotted 95 % confidence intervals). Ellenberg light availability index and AM morphotype were obtained from the literature (see the Materials and Methods). The single Paris-type AM plant species are represented by mean values. Standard deviations are omitted for clarity. Symbol size reflects the sample size of the Paris-type species (n = 1–31, see Supplementary data Table S3). The figure counts only Paris-type AM species with data on ε ¹³C and Ellenberg light availability values. Paris-type plant species that were significantly ¹³C enriched: (A) A.fil. Athyrium filix-femina, D.fil. Dryopteris filix-mas, E. syl. Equisetum sylvaticum, P.vul. Polypodium vulgare, E.tel. Equisetum telmateia, E.arv. Equisetum arvense, E.flu. Equisetum fluviatile; (B) O.ace. Oxalis acetosella, M.per. Mercurialis perennis, P.qua. Paris quadrifolia, L.num. Lysimachia nummularia, M.nut. Melica nutans, G.syl. Geranium sylvaticum, T.com. Tamus communis, A.maj. Astrantia major, G.lut. Gentiana lutea, S.pec. Scandix pecten-veneris, L.mut. Ligusticum mutellina, M.ath. Meum athamanticum, B.ere. Bromus erectus.