Wheat, canola and grain legume access to soil phosphorus fractions differs in soils with contrasting phosphorus dynamics

TLDR: It is hypothesized that insoluble P fractions may be more available to non-legume plants in alkaline soils due to increased dissolution of the dominant calcium(Ca)-P pool into depleted labile P pools, whereasnon-legumes may have limited access to insolubleP fractions in iron(Fe)- and aluminium(Al)-P dominated acid soils.

Abstract: Despite the high phosphorus (P) mobilizing capacity of many legumes, recent studies have found that, at least in calcareous soils, wheat is also able to access insoluble P fractions through yet unknown mechanism(s). We hypothesized that insoluble P fractions may be more available to non-legume plants in alkaline soils due to increased dissolution of the dominant calcium(Ca)-P pool into depleted labile P pools, whereas non-legumes may have limited access to insoluble P fractions in iron(Fe)- and aluminium(Al)-P dominated acid soils. Four crop species (faba bean, chickpea, wheat and canola) were grown on two acid and one alkaline soil under glasshouse conditions to examine rhizosphere processes and soil P fractions accessed. While all species generally depleted the H2O-soluble inorganic P (water Pi) pool in all soils, there was no net depletion of the labile NaHCO3-extractable inorganic P fraction (NaHCO3 Pi) by any species in any soil. The NaOH-extractable P fraction (NaOH Pi) in the alkaline soil was the only non-labile Pi fraction depleted by all crops (particularly canola), possibly due to increases in rhizosphere pH. Chickpea mobilized the insoluble HCl Pi and residual P fractions; however, rhizosphere pH and carboxylate exudation could not fully explain all of the observed Pi depletion in each soil. All organic P fractions appeared highly recalcitrant, with the exception of some depletion of the NaHCO3 Po fraction by faba bean in the acid soils. Chickpea and faba bean did not show a higher capacity than wheat or canola to mobilize insoluble P pools across all soil types, and the availability of various P fractions to legume and non-legume crops differed in soils with contrasting P dynamics.