Root or shoot nitrate assimilation in terrestrial vascular plants - does it matter?

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.

Automated summary

This study collates and analyzes data from the literature regarding the effects of genotype and environment on the partitioning of NO3- assimilation between root and shoot of terrestrial vascular plants. The results show that different plant species have different proportions of NO3- assimilation in their roots and shoots under different concentrations of soil NO3-. Factors such as high NH4+ supply, mycorrhizal infection, and parasitic plant infection can increase the proportion of shoot NO3- assimilation, while abiotic stress and elevated atmospheric CO2 can decrease it. Resolving the discrepancies between different studies is an important area for future research.