How much nitrogen can plants absorb from the soil yearly?

Previous research determined that nutrients such as nitrogen are an important co-factor of plant growth, and therefore, plant carbon sequestration. Substantial efforts have been devoted to introduce nitrogen as a co-factor in the most used carbon cycle (CMIP) and vegetation models (TRENDY). Despite of it, the amount of nitrogen plants are taking from the soil to be part of its tissue remains unquantified.

Most of the nitrogen on earth can be found in the atmosphere in gas form (N2), comprising more than 70% of the atmosphere. Even if abundant, N2 is not available to be absorbed by plants, and biotic soil processes led by microorganisms are necessary to transform this nitrogen in plant-friendly forms such as ammonium or nitrate. Aside from these nitrogen-fixing microorganisms, we can also find other microorganisms that compete for organically bound nitrogen of which only part of it is going to available for plants to be absorbed.

We are aiming to leverage published field data accounting for plant biomass increase in roots, wood (if woody plant) and leaves as well as for the nitrogen contained in these tissues to train a machine-learning model. There we will be determining the drivers that affect this relation, creating an upscaled map of nitrogen uptake worldwide and comparing the differences these results suppose to global change calculations.

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Related papers:

Fernández-Martínez M, Vicca S, Janssens IA, Sardans J, Luyssaert S, Campioli M, Chapin FS III, Ciais P, Malhi Y, Obersteiner M et al. 2014. Nutrient availability as the key regulator of global forest carbon balance. Nature Climate Change 4: 471–476.

Hungate, B.A., Dukes, J.S., Shaw, M.R., Luo, Y., Field, C.B. Nitrogen and Climate change. Science 302, 1512-1513, (2003)

Terrer, C., Jackson, R.B., Prentice, I.C. et al. Nitrogen and phosphorus constrain the CO2 fertilization of global plant biomass. Nat. Clim. Chang. 9, 684–689 (2019).