It was interesting to learn that prince’s pine (Chimaphila umbellata), the subject of my last post, was a mycoheterotroph. Then as I delved further into this shrubby wildflower I discovered that prince’s pine, also known as pipsissewa, is a mixotroph.
Mycoheterotrops obtain their nutrition indirectly from another plant via the mycorrhiza of fungi (think mushrooms). The mycorrhizal fungi attach to the roots of a photosynthetic host (prince’s pine can have many different plants as a host) and also to the roots of prince’s pine and form at bridge between the host plant and prince’s pine – host to fungi to prince’s pine – thus assisting in the transfer of organic nutrients to prince’s pine. Studies have shown that all prince’s pine roots have fungi hyphae complexes.
Autotrophs are plants that are capable of synthesizing their organic matter from inorganic nutrients, most often through photosynthesis. Heterotrophs (mycoheterotrophs included) cannot obtain their organic matter from inorganic sources thus must obtain their carbon from other organic sources. A mixotroph can produce its own organic matter and also utilizes other organic sources – a combination auto and heterotroph.
Usually we think of heterotrophs as plants without chlorophyll (see Indian Pipe and Indian Pipe Flower). Yet prince’s pine is definitely a green plant with chlorophyll. Using stable isotopes of carbon and nitrogen the sources of these two elements were identified in prince’s pine. The carbon isotope “signature” of prince’s pine resembled that of autotrophs while the nitrogen signature was that of a mycoheterotroph. Therefore it seems as though the organic matter in prince’s pine derives from both autotrophic and heterotrophic processes, making prince’s pine a mixotroph. The mychorrhizal contribution appears less significant once the plant begins to photosynthesize.
One suggestion as to why prince’s pine obtains organic matter by both methods suggests that during initial development prince’s pine is mycoheterotrophic and that once the plant is established it becomes autotrophic. Prince’s pine seeds are minescule, like dust, and possibly contain minimal food reserves for the developing plant. The mycorrhizal bridge provides nourishment for the young plant, which can then begin to photosynthesize its own organic matter once established. Like many other mycorrhizal plants, it is difficult or impossible to germinate prince’s pine in sterile soil or soil not native to its habitat.
A fascinating plant!