The carbon bonus of organic nitrogen enhances nitrogen use efficiency of plants.


The importance of organic nitrogen (N) for plant nutrition and productivity is increasingly being recognized. Here we show that it is not only the availability in the soil that matters, but also the effects on plant growth. The chemical form of N taken up, whether inorganic (such as nitrate) or organic (such as amino acids), may significantly influence plant shoot and root growth, and nitrogen use efficiency (NUE). We analysed these effects by synthesizing results from multiple laboratory experiments on small seedlings (Arabidopsis, poplar, pine and spruce) based on a tractable plant growth model. A key point is that the carbon cost of assimilating organic N into proteins is lower than that of inorganic N, mainly because of its carbon content. This carbon bonus makes it more beneficial for plants to take up organic than inorganic N, even when its availability to the roots is much lower - up to 70% lower for Arabidopsis seedlings. At equal growth rate, root:shoot ratio was up to three times higher and nitrogen productivity up to 20% higher for organic than inorganic N, which both are factors that may contribute to higher NUE in crop production.





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Publication Info

Franklin, Oskar, Camila Aguetoni Cambui, Linda Gruffman, Sari Palmroth, Ram Oren and Torgny Näsholm (2017). The carbon bonus of organic nitrogen enhances nitrogen use efficiency of plants. Plant, cell & environment, 40(1). pp. 25–35. 10.1111/pce.12772 Retrieved from

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Sari Palmroth

Research Professor in the Division of Environmental Science and Policy

Dr. Palmroth's research focuses on the effects of resource availability and climatic variability on carbon uptake and allocation of individual shoots, trees and forest ecosystems. She studies ecophysiological processes in trees from leaf to stand scales, with special emphasis on conifers. In particular, Dr. Palmroth is interested in the radiative transfer in forest canopies, how the radiation regime is affected by conifer shoot structure, and what the feedbacks are between availability of solar energy and allocation on carbon and nitrogen within canopies. She is also interested in how the carbon fixed in photosynthesis is allocated between above and belowground pools and what are the possible interaction effects on the allocation of the availabilities of nutrients and water and the level of atmospheric [CO2].


Ram Oren

Nicholas Distinguished Professor of Earth Systems Science

With his graduate students, Oren quantifies components of the water cycle in forest ecosystems, and their responses to biotic and abiotic factors. Relying on the strong links between the carbon and water cycles, he also studies the components of the carbon flux and their response to these factors. Climate variability, including variations in air temperature, vapor pressure deficit, incoming radiation and soil moisture, and environmental change, including elevated atmospheric carbon dioxide, affect the intra- and inter-annual dynamics, and amounts of water used by forest ecosystems, and their spatial distribution, as well as carbon uptake and sequestration. In turn, the variation of water flux influence the temporal and spatial partitioning of incoming radiation between latent and sensible heat. The flow of water from soil through plant leaves into the atmosphere, and the exchange of water for CO2 absorbed from the atmospheric, are among the processes theoretically best understood in plant and ecosystem physiology. Using these theories, local mass balance approaches, and detailed measurements of water and carbon flux and driving variables in the soil, plants, and the atmosphere, Oren has been attempting to predict the likely responses of forest ecosystems, from the equator to the arctic circle, to environmental change and management.

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