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

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