Crop species differ in root plasticity response to localised P supply

The effect of localised phosphorus (P) fertiliser placement and in particular, deep P fertiliser placement, on the comparative root growth and P uptake of fibrous vs tap-rooted crops is not known. In this study, we examined the root growth and P uptake of wheat (Triticum aestivum L.), canola (Brassica napus L.), and narrow-leaf lupin (Lupinus angustifolius L.) in a split-root system and in columns with deep (19 cm) or shallow (5 cm) P fertiliser sources in glasshouse conditions. In the split-root system, plants of all three species grown under heterogeneous soil P conditions absorbed more P and produced greater root and shoot biomass than those under homogeneous P supply. Root plasticity differed between species under heterogeneous soil P supply: canola and wheat allocated relatively more root biomass and root length to the high P zone than narrow-leaf lupin. In the column experiment, there was no difference in the amount of P accumulated in shoots of any crops grown in the deep vs shallow P fertiliser treatments. Root proliferation occurred within the shallow and deep-P fertiliser bands in all three species; however, root distribution above or below the bands did not differ between deep or shallow P fertiliser treatments in any species. Whilst root plasticity responses to heterogeneous soil P supply differed among species, root architecture (fibrous vs taproot) did not confer any advantage or disadvantage to the acquisition of P from deep vs shallow P fertiliser bands. Moreover, whilst roots proliferate in the vicinity of P fertiliser bands, root distribution outside of the bands appears to remain unaltered in both fibrous and tap-rooted crops during early growth.