Shade and drought increase fungal contribution to partially mycoheterotrophic terrestrial orchids Goodyera pubescens and Tipularia discolor

Many photosynthetic plants supplement photosynthetic carbon with fungal carbon, but the mechanisms that govern dependence on mycoheterotrophic carbon are poorly understood. We used exclusion shelters to manipulate water and light availability to plants of the terrestrial orchids Goodyera pubescens and Tipularia discolor. We tracked changes in δ13C from photosynthesis and δ15N acquired from soil-derived inorganic nitrogen versus mycoheterotrophy, along with direct measures of photosynthesis in T. discolor. We hypothesized that shade would increase dependence on mycoheterotrophy compared to reference plants, while drought would decrease both photosynthesis and the abundance of potential mycorrhizal fungi. Drought and shade enriched 13C and 15N in both G. pubescens and T. discolor, compared to control plants, indicating increased fungal contribution to orchid tissues. Physiological measurements of T. discolor leaves showed that dark respiration, water use efficiency, and relative electron transport rate did not vary significantly, but shaded plants had greater quantum efficiency, suggesting they were light-limited. Light saturated photosynthesis of T. discolor leaves was lower in both shaded and drought-treated plants, indicating lower photosynthetic capacity, and likely greater dependence on mycoheterotrophy and corresponding enrichment in 13C and 15N. This study documented changes in orchid dependence on fungal carbon in response to manipulated environmental conditions. Both shade and drought increased the dependence of both orchids on mycoheterotrophically derived carbon and nitrogen.

The same anthocyanins served four different ways: Insights into anthocyanin structure-function relationships from the wintergreen orchid, Tipularia discolor

Over 500 unique anthocyanins have been described to date, which vary in color, antioxidant, light-attenuating, and antimicrobial properties. Identification of anthocyanin chemical structure may therefore serve as an important clue to their in situ function in plants. We characterized the histological and chemical structures of anthocyanins associated with diverse leaf color patterns in the terrestrial orchid, Tipularia discolor, as a step towards understanding their ultimate function. Tipularia discolor produces a single wintergreen leaf in autumn, which is drab brown in color during expansion. Upper (adaxial) surfaces of fully-expanded leaves may be green, purple-spotted, or solid purple, while lower (abaxial) surfaces are bright magenta. Our results showed that the same three cyanidin 3,7,3'-triglucosides, in similar concentrations and proportions, accounted for coloration in each of these cases, and that different colors result from differences in histological location of anthocyanins (i.e. abaxial/adaxial epidermis, mesophyll). Anthocyanins with 3,7,3' linkage positions are rare in plants, occurring only within the orchid subfamily Epidendroideae, to which Tipularia belongs. These results are important to the discussion of anthocyanin structure-function because they serve as a reminder that 1) plants may employ the same anthocyanins in different anatomical locations to achieve a broad range of colors (and potentially adaptive functions), and 2) anthocyanin chemical structure and anatomical location are influenced by phylogenetic inertia, as well as natural selection.