Root or shoot nitrate assimilation in terrestrial vascular plants – does it matter?
2022
Andrews, Mitchell | Raven, John A.
BACKGROUND: Most terrestrial vascular plants can assimilate soil obtained NO₃⁻ in their root and shoot. SCOPE: Data from the literature are collated and analysed with respect to genotype and environmental effects on the partitioning of NO₃⁻ assimilation between root and shoot of terrestrial vascular plants. CONCLUSIONS: Temperate evergreen woody species in the Ericaceae and Pinaceae carry out most of their NO₃⁻ assimilation in the root when growing in low (0.5 mM) up to at least 5 mM soil NO₃⁻. The root is the main site of NO₃⁻ assimilation for temperate deciduous woody species and perennial and annual herbaceous legume species at 0.5–1 mM NO₃⁻ but for many, shoot assimilation increases in importance with increased NO₃⁻ supply. Temperate perennial grasses and annual non-legume species and tropical/ sub-tropical species regardless of life-form, carry out a substantial, usually major proportion of their NO₃⁻ assimilation in shoots at NO₃⁻ concentrations above 0.5 mM. Furthermore, high NH₄⁺ supply, mycorrhizal infection and infection by parasitic plants can increase the proportion of total plant NO₃⁻ assimilation carried out in the shoot while abiotic stress and elevated atmospheric [CO₂] can cause this to decrease. Shoot NO₃⁻ assimilation is an advantage under non-stress conditions due to its positive effect on leaf expansion but can be a disadvantage under freezing and chilling stress conditions. Increased reliance on root NO₃⁻ assimilation at elevated CO₂ was associated with increased and conversely decreased plant growth and NO₃⁻ assimilation depending on study. Resolution of these different findings across studies is an important area for further research.
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