Mechanism of C/N competition between legume hosts and parasitic plants

Research Project

Project/Area Number	23K05916
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Multi-year Fund
Section	一般
Review Section	Basic Section 45040:Ecology and environment-related
Research Institution	University of Tsukuba
Principal Investigator	Irving Louis 筑波大学, 生命環境系, 助教 (60597178)
Project Period (FY)	2023-04-01 – 2026-03-31
Project Status	Granted (Fiscal Year 2023)
Budget Amount *help	¥4,290,000 (Direct Cost: ¥3,300,000、Indirect Cost: ¥990,000) Fiscal Year 2025: ¥650,000 (Direct Cost: ¥500,000、Indirect Cost: ¥150,000) Fiscal Year 2024: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000) Fiscal Year 2023: ¥2,340,000 (Direct Cost: ¥1,800,000、Indirect Cost: ¥540,000)
Keywords	Orobanche / parasite / nitrogen / carbon / isotope / parasitic plant / legume / rhizobia / C/N balance / N-fixation
Outline of Research at the Start	This research explores the influence of environmental and spatial factors on the relationships between the holoparasitic plant Orobanche minor, N-fixation, and the performance of the red clover host.
Outline of Annual Research Achievements	I completed the first phase of the research and am preparing a manuscript for publication in a high-impact journal. Host growth and nutrient uptake were severely limited where nutrients were supplied to parasitized roots. I have started three new direction, 1) effect of N level and parasitism on host photosynthesis, 2) effect of parasite / rhizobia position on the host-parasite relationship, 3) developing a clean system for host - parasite isotope tracing studies. For 1, we found that N supply leads to a strong suppression in both parasite establishment and parasite growth. However, low level N supply caused a decline in photosynthetic rates. For 2, we found that parasite mass was strongly increased when grown near the bottom of the root box, although the mechanism is unknown. We have developed two plausible hypotheses, either that the parasite is directly taking nutrients up from the surrounding media, or that N fixed in the upper part of the root is being transported to the parasite. For 3, we have established a system, although parasite necrosis is an issue. In the next few months we will develop an isotope labelling system for 13CO2 in order to quantify host to parasite carbon flux kinetics.
Current Status of Research Progress	Current Status of Research Progress 2: Research has progressed on the whole more than it was originally planned. Reason There are no issues with the project, although it is generating many surprising results which require some reevaluation of the original plan.
Strategy for Future Research Activity	This summer I will measure the effect of parasite number of host photosynthesis (low vs. high rate of parasitism) in collaboration with Dr. Shinya Wada (Tohoku UNiv). We will also try time-series 13C labeling to investigate host --> parasite C transfer kinetics, and the effect of environmental conditions. I will evaluate nutrient uptake and parasite capture of nutrients supplied above or below the point of attachment. It was unexpectedly difficult to do spatial analysis of parasite / rhizobia interactions, because the rhizobia could not be contained in one part of the root system. I will improve my root box design and improve rhizobia-handling procedures to counter these issues.