Plant-mediated processess to acquire nutrients: nitrogen uptake by rice plants

The ways in which root-soil interactions can control nutrient acquisition b y plants is illustrated by reference to the N nutrition of rice. Model calc ulations and experiments are used to assess how uptake is affected by root properties and N transport through the soil. Measurements of the kinetics o f N absorption and assimilation and their regulation, and of interactions b etween NH4+ and NO3- nutrition, are described. It is shown that uptake of N from the soil-as opposed to N in ricefield floodwater which can be absorbe d very rapidly but is otherwise lost by gaseous emission-will often be limi ted by root uptake properties. Rice roots are particularly efficient in abs orbing and assimilating NO3-, and NH4+ absorption and assimilation are stim ulated by NO3-. The uptake of NO3- formed in the rice rhizosphere by root-r eleased O-2 may be more important than previously thought, with beneficial consequences for rice growth. Other root-induced changes in the rice rhizos phere and their consequences are discussed.