The role of root size versus root efficiency in phosphorus acquisition in rice

In rice, genotypic differences in phosphorus (P) uptake from P-deficient soils are generally proportional to differences in root biomass or surface area (RSA). It is not known to what extent genotypic variation for root efficiency (RE) exists or contributes to P uptake. We evaluated 196 rice accessions under P deficiency and detected wide variation for root biomass which was significantly associated with plant performance. However, at a given root size, up to 3-fold variation in total biomass existed, indicating that genotypes differed in how efficiently their root system acquired P to support overall plant growth. This was subsequently confirmed, identifying a traditional genotype, DJ123, with 2.5-fold higher RE (32.5 µg P cm−2 RSA) compared with the popular modern cultivar IR64. A P depletion experiment indicated that RE could not be explained by P uptake kinetics since even IR64 depleted P to