A multi-method approach to assessing carbon and nitrogen nutritional strategies and response to disturbance of mycoheterotrophic ericaceae

Mycoheterotrophy is a nutritional strategy where plants obtain some portion of their required carbon through mycorrhizal fungi. This four-year study assessed ¹³C and ¹⁵N stable isotopes, gas-exchange data and population densities of putative partial (PMH) and full mycoheterotrophic (MH) ericaceous species relative to assorted autotrophs across various habitats and disturbance levels. Two of the putative PMH Pyroleae species exhibited approximately 30% MH carbon gains; however, some data indicated that ¹³C enrichment in Pyroleae species may result from unique autotrophic physiology or metabolism rather than fungal carbon acquisition. Regardless of nutritional status, the Pyroleae appeared sensitive to high irradiance. Long-term exposure to excess light may have contributed to photosynthetic impairment and population declines observed in clearcuts, where residual vegetation appeared to promote resilience by providing shade and nitrogen obtained through mycorrhizal fungi. This study provides valuable insight into physiological and environmental limitations of plant species that are partially to fully mycoheterotrophic.