Nitrogen-fixing plant ecology: factors limiting the nitrogen fixing trait

Thumbnail Image
Chen, Haoran
Journal Title
Journal ISSN
Volume Title
In the nitrogen-fixing clade, only 10 out of 28 plant families retain the nitrogen fixation trait. It is thought that the nitrogen fixation has been lost repeatedly since it evolved. Exploring the potential abiotic and biotic factors that trigger the loss of nitrogen-fixing traits is critical to understanding the evolution and ecology of plants. I designed three studies to examine how nitrogen-fixing plants respond to N deposition, different levels of CO2, herbivore damage, and less-effective symbionts. For the first study I grew three nitrogen fixers (Alnus incana ssp. rugosa, Alnus viridis ssp. crispa, and Alnus rubra) and their close non-nitrogen fixing relatives (Betula pumila, Betula papyrifera, Betula glandulosa) at ancient (1600 ppm) or present (400 ppm) CO2 over a range of soil N levels, equivalent to 0, 10, 50, and 200 kg N ha-1 year-1. I found nitrogen-fixing plants were less competitive as soil N increased compared with non-N fixers, but at ancient CO2 levels nitrogen-fixing plants are at an advantage at higher soil N levels. The seconded study explored the interaction between Alnus incana ssp. rugosa and Orgyia leucostigma under ambient (400 ppm), future (800 ppm), and ancient (1600 ppm) CO2. Herbivores preferred to feed on nodulated plant leaves grown at 400 ppm and 1600 ppm when given a choice, compared with non-nodulated leaves. At 800 ppm CO2 nodulated plants accumulated more total phenolic compounds in response to herbivore damage than plants in the non-Frankia and non-herbivore treatments. The third study examined if Alnus spp. can select against less-effective symbiont via partner choice or sanctioning. In a co-inoculation experiment, host plants could not prevent the less effective sp+ Frankia from entering roots when inoculated with a mixture of effective (sp-) and less effective (sp+) Frankia. When plant roots were inoculated with sp+ Frankia and exposed to Argon to induce Frankia cheating, specific nodule mass was not reduced. However, Argon-treated half roots had less specific nodule activity and specific nodule mass when inoculated with sp- Frankia. My studies suggest that increasing N deposition, dropping CO2, and the less/ineffective symbionts might trigger the loss of the nitrogen fixing trait.
Nitrogen-fixing plants, Elevated CO2, Herbivores damage, Total phenolic compounds, Partner choice, Host sanctions, Nitrogen deposition
Chen, H., & Markham, J. (2021). Ancient CO2 levels favor nitrogen fixing plants over a broader range of soil N compared to present. Scientific reports, 11(1), 3038
Chen, H., & Markham, J. (2021). The interactive effect of elevated CO2 and herbivores on the nitrogen-fixing plant Alnus incana ssp. rugosa. Plants, 10(3), 440.
Chen, H., & Markham, J. (2020). Using microcontrollers and sensors to build an inexpensive CO2 control system for growth chambers. Applications in plant sciences, 8(10), e11393