Endophytic bacteria and rare earth elements; promising candidates for nutrient use efficiency in plants

Nutrient use efficiency (NUE) depends on the plant's ability to take up nutrients efficiently from the soil, but also depends on internal transport, storage and remobilization of nutrients. Nitrogen (N) is a fundamental element regulating plant growth and development. Plants have evolved inorganic and organic N-uptake systems to cope with heterogeneous N availability in the soil. However, NUE is dependent on root growth and root architecture. Endophytic bacteria have a direct influence on root growth and increase nutrient uptake. Under reciprocal exchange, trading carbon for nutrients, plant and bacteria establish a symbiotic association. In this chapter we will address how endophytic bacteria might contribute to efficient nutrient uptake, especially organic nitrogen, through bacterial cell degradation or by externally activating nitrogen transporters. Also, here we propose the use of rare earth elements as an option for improving NUE in plants and their possible use as fertilizers.