Genomic Science Program
U.S. Department of Energy | Office of Science | Biological and Environmental Research Program

EndoPopulus: Endophyte Inoculation Alters Whole-Plant Physiology and Growth Dynamics of Populus Under Nitrogen-Deficient Condition

Authors:

Sun Woo Chung1* (jsw599@uw.edu), Darshi Banan1, Shubroto K. Sarkar1, Carter Corcoro1, Sriram Parasurama1, Andrew W. Sher1, Robert J. Tournay1, Jayde Aufrecht2, Amir H. Ahkami2, Soo-Hyung Kim1, Sharon L. Doty1

Institutions:

1University of Washington–Seattle; 2Pacific Northwest National Laboratory

Goals

This project aims to understand how the microorganisms in the Populus tree microbiome affect the host plant health and stress tolerance. The team combines plant physiology experiments under normal, nutrient-limited, and water-limited conditions with field and greenhouse data for crop modeling. The process-based model will guide further examination of microbiology, metabolomic, and transcriptomic data, resulting in a system-level understanding of the plant-endophyte interactions from the molecular to the canopy level.

Abstract

Endophyte inoculation has a potential to improve biofuel crop sustainability by increasing resource use efficiency and stress tolerance, possibly reducing fresh water and fertilizer needs. Previous research demonstrated that Salicaceae endophytes improved water use efficiency in poplar plants under drought conditions (Banan et al. 2024). These endophytes are also known to fix atmospheric nitrogen and alter metabolite biosynthesis, processes that can boost crop productivity. In this study, researchers investigated the morphological changes and resource allocations in poplar trees inoculated with Salicaceae endophytes under nitrogen deficiency at multiple scales ranging from tissue and organ to whole plant. Nisqually-1 Populus trichocarpa were mock-inoculated or inoculated with the endophyte consortia as described by Banan et al. (2024). Plants were irrigated daily with either 10 millimeter (low nitrogen; LN) or 40 mM ammonium nitrate [NH4NO3; high nitrogen (HN)] for 150 days. The length of plant shoots and the number of fully expanded leaves were monitored weekly. Upon detecting differences in these data, additional measurements were taken of leaf size and leaf chlorophyll content by a SPAD meter, and their ratio were assessed for entire leaves weekly. Around 60 days after cultivation (DAC), the endophyte-inoculated plants under LN exhibited taller growth and more leaves than non-inoculated plants. The inoculated plants maintained higher shoot length up to harvest, but leaf numbers equalized by 150 DAC. Under HN, endophyte inoculation had no effect on the shoot length and leaf number. Total leaf area per plant was higher in inoculated plants around 60 DAC, regardless of NH4NO3 levels. This difference became larger up to harvest under LN but diminished after 100 DAC under HN. Chlorophyll content followed a similar trend.

Across treatments, the ratio of chlorophyll content to leaf area decreased over time. Under LN, inoculated plants initially had a higher ratio, but it declined rapidly after 100 DAC, reaching levels similar to non-inoculated plants. Under HN, inoculation did not affect the ratio. Inoculated plants exhibited greater total dry biomass than non-inoculated plants, regardless of NH4NO3 levels. Under LN, inoculation increased stem dry mass with no effect on root or leaf biomass.

Under HN, stem and leaf biomass trends were similar to LN, but inoculated plants also showed higher root biomass, resulting in a higher root-to-shoot ratio. These results suggest that endophyte inoculation aids plant adaptation to stress, enhancing host productivity and resource use efficiency; larger leaves and increased chlorophyll content suggest this adaptation promotes growth under nitrogen-deficient conditions. These physiological data will be used for process-based modeling to quantify the potential of endophytes to enhance biofuel feedstock production.

References

Banan, D., et al. 2024. “Endophyte Mediated Populus trichocarpa Water Use Efficiency Is Dependent on Time of Day and Plant Water Status,” Phytobiomes Journal. DOI:10.1094/PBIOMES-11-22-0077-R.

Funding Information

This research was supported by the DOE Office of Science, BER program, grant no. DE-SC0021137.