title: The tiny-leaved orchid Cephalanthera subaphylla obtains most of its carbon via mycoheterotrophy.
abstract: The evolution of mycoheterotrophy has been accompanied by extreme reductions in plant leaf size and photosynthetic capacity. Partially mycoheterotrophic plants, which obtain carbon from both photosynthesis and their mycorrhizal fungi, include species with leaves of normal size and others that are tiny-leaved. Thus, plant species may lose their leaves in a gradual process of size reduction rather than through a single step mutation. Little is known about how the degree of mycoheterotrophy changes during reductions in leaf size. We compared the degree of mycoheterotrophy among five Japanese Cephalanthera species, four with leaves of normal size (Cephalanthera falcata, Cephalanthera erecta, Cephalanthera longibracteata and Cephalanthera longifolia), one with tiny leaves (Cephalanthera subaphylla), and one albino form of C. falcata (as reference specimens for fully mycoheterotrophic plants). The levels of mycoheterotrophy were determined by stable isotope natural abundance analysis. All Cephalanthera species were relatively enriched in13C and15N in comparison with surrounding autotrophic plants. Cephalanthera subaphylla was strongly enriched in13C and15N to levels similar to the albinos. Species with leaves of normal size were significantly less enriched in13C than C. subaphylla and the albinos. Thus, C. subaphylla was strongly mycoheterotrophic, obtaining most of its carbon from mycorrhizal fungi even though it has tiny leaves; species with leaves of normal size were partially mycoheterotrophic. Hence, during the evolutionary pathway to full mycoheterotrophy, some plant species appear to have gained strong mycoheterotrophic abilities before completely losing foliage leaves.
authors.affiliation: Botanical Gardens, Tohoku University, 12-2 Kawauchi, Aoba-ku, Sendai, 980-0862, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Sakamoto
authors.affiliation: Department of Agriculture, Saga University, 1 Honjo-machi, Saga, 840-8502, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Ogura-Tsujita
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 1-1 Amamiya-machi, Tsutsumidori, Aoba-ku, Sendai, 981-8555, Japan.
authors.forename: Kinuko
authors.initials: K
authors.lastname: Ito
authors.affiliation: Department of Biology, Graduate School of Science, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 657-8501, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Suetsugu
authors.affiliation: Department of Science, Yamagata University, 1-4-12 Kojirakawa, Yamagata, 990-8560, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Yokoyama
authors.affiliation: College of Agriculture, Tamagawa University, 6-1-1 Tamagawagakuen, Machida, 194-8610, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Yamazaki
authors.affiliation: Tsukuba Botanical Garden, National Museum of Nature and Science, 4-1-1 Amakubo, Tsukuba, 305-0005, Japan.
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Yukawa
authors.affiliation: Botanical Gardens, Tohoku University, 12-2 Kawauchi, Aoba-ku, Sendai, 980-0862, Japan. maki@m.tohoku.ac.jp.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Maki
mesh_terms: D002244:Carbon / Q000378:metabolism*; D005658:Fungi / Q000378:metabolism*; D052836:Heterotrophic Processes; D007564:Japan; D009584:Nitrogen / Q000378:metabolism*; D029595:Orchidaceae / Q000033:anatomy & histology / Q000378:metabolism* / Q000382:microbiology*; D018515:Plant Leaves / Q000033:anatomy & histology; D013045:Species Specificity; D013559:Symbiosis
chemical_list: D002244:Carbon; D009584:Nitrogen
keywords: Cephalanthera; Leaf size; Mycoheterotrophy; Orchidaceae; Stable isotope