Photon costs of shoot and root NO, and root NH, assimilation in terrestrial vascular plants considering associated pH regulation, osmotic and ontogenetic effects.

The photon costs of photoreduction/assimilation of nitrate (NO) into organic nitrogen in shoots and respiratory driven NO and NH assimilation in roots are compared for terrestrial vascular plants, considering associated pH regulation, osmotic and ontogenetic effects. Different mechanisms of neutralisation of the hydroxyl (OH) ion necessarily generated in shoot NO assimilation are considered. Photoreduction/assimilation of NO in shoots with malic acid synthesis and either accumulation of malate in leaf vacuoles or transport of malate to roots and catabolism there have a similar cost which is around 35% less than that for root NO assimilation and around 20% less than that for photoreduction/assimilation of NO, oxalate production and storage of Ca oxalate in leaf vacuoles. The photon cost of root NH assimilation with H efflux to the root medium is around 70% less than that of root NO assimilation. These differences in photon cost must be considered in the context of the use of a combination of locations of NO assimilation and mechanisms of acid-base regulation, and a maximum of 4.9-9.1% of total photon absorption needed for growth and maintenance that is devoted to NO assimilation and acid-base regulation.

© 2022. The Author(s), under exclusive licence to Springer Nature B.V.