Plant strategy of root system architecture and exudates for acquiring soil nutrients

Abstract

Vascular plants develop diverse root system architectures and exudates to facilitate acquisition of soil nutrients (nitrogen and phosphorus). Plant species have inherently specific properties of root system architectures and exudates, but some plants exhibit high plasticity to respond to spatiotemporal variations in soil nutrient forms and availability. This paper synthesizes evidence on how plant species diversity and root plasticity contribute to soil nutrient mobilization and uptake in plants from the tropics to the Arctic with varying plant species diversity. The development of finer roots in the surface soil is a well-known strategy for the acquisition of limited nutrients (especially phosphorus), but the allocation of roots foraging “nutrient hotspots” in deeper soil (podzolic soil or permafrost-affected soils) is an alternative strategy for coniferous trees tested in the Arctic and boreal forests. This contrasts with findings in tropical forests, where diverse plant species with different capacities of organic acid exudation coexist and species composition shifts in response to phosphorus deficiency. In particular, high malate exudation from roots and rhizosphere microbes stimulates phosphorus solubilization, aluminum detoxification, and lignin degradation in acidic soils. The diversity and plasticity of the root system architecture, root exudation, and the flexibility of nutrient sources mitigate nutrient limitation in soil. Root plasticity facilitating soil nutrient acquisition has a large impact on biogeochemistry and soil formation, such as podzolization, in the long term.