The model plant thale cress acquires organic nitrogen from the soil, although its roots do not form symbiosis with mycorrhizal fungi. This is shown in a study, led by SLU researchers. They also show that plants can acquire organic nitrogen in competition with microorganisms in soil, which previously has been questioned. This means that organic nitrogen can contribute to the plant’s nitrogen supply, and raises the question if agricultural crops could be modified to become more efficient in using organic nitrogen as a source of nutrients.
The classic science on plant nutrition states that plants acquire nitrogen from the soil as nitrate or ammonium, or as nitrogen gas if the plant forms symbiosis with nitrogen-fixing bacteria. Today we know that there are plants that also can make use of organic nitrogen, but the consensus has been that it only applies to certain mycorrhiza-forming plants growing in nutrient-poor soils. Together with colleagues from Austria and Australia the SLU researchers show that a plant that does not form mycorrhiza acquires organic nitrogen when grown in nutritious agricultural soil.
The findings show that the plant is dependent on a specific protein for this to work. The protein is an amino acid transporter, and the researchers have performed a number of experiments on genetically modified thale cress (Arabidopsis thaliana) that either lack the transporter or over produces it.
Torgny Näsholm is Professor in ecophysiology at the Swedish university of agricultural sciences in Umeå, and he led the study.
– We grew the plants in greenhouses in agricultural soil, and could follow the way of the amino acid glutamine from the soil into the plant by labelling the glutamine with carbon and nitrogen isotopes. It turned out that the uptake of the amino acid is much more efficient in plants that overproduce the amino acid transporter, and very low in plants lacking the transporter, he explains.
Additionally, the plants that were lacking the transporter had the lowest carbon/nitrogen ratios, and the plants overproducing the transporters had the highest ratios. Theoretically the amino acids should result in a higher carbon concentration, which indicates that the plants have been taking up organic nitrogen from the soil continuously.
– This study is a milestone in our research. With the use of genetically modified model plants we have been able to show that amino acids in soil are used as nitrogen sources by plants. We also aim to increase the plant capacity to take up nitrogen from the soil, and our results show that an optimization of organic nitrogen uptake is a possible way to achieve this, says Torgny Näsholm.
Thale cress is not an agricultural crop, but a model plant which is often used to predict the effects of genetic modifications in agricultural plant species. The research group now investigates how the uptake of organic nitrogen can be improved in potato.
– We are now testing if it is possible to use the same strategy to increase the uptake of organic nitrogen in an agricultural crop. We have propagated modified potato clones to see if we get the same increase in potato as in thale cress.
Ganeteg, U., Ahmad, I., Jämtgård, S., Aguetoni-Cambui, C., Inselsbacher, E., Svennerstam, H., Schmidt, S., and Näsholm, T. (2017) Amino acid transporter mutants of Arabidopsis provides evidence that a non-mycorrhizal plant acquires organic nitrogen from agricultural soil. Plant, Cell & Environment, 40: 413–423. doi: 10.1111/pce.12881.