Plant Species Rather than Elevated Atmospheric CO2 Impact Rhizosphere Properties and Phosphorus Fractions in a Phosphorus-Deficient Soil

By 2050, elevated atmospheric CO2 (eCO(2)) could stimulate plant growth, but dwindling phosphorus (P) stocks in the soil could limit growth. However, little is known about how eCO(2) could affect soil P availability and dynamics in P-poor soils. Here, we conducted a 6-week pot experiment where three plant species were grown in a low-P soil under ambient (390 ppm) and eCO(2) (700 ppm) to investigate plant growth, rhizosphere properties, and changes in soil P fractions. Our results showed that under P deficiency, plant biomass, P uptake, and rhizosphere properties did not respond to eCO(2). Changes were noted by plant species. Compared to the control soil (unplanted pots), rhizosphere pH decreased the most under wheat, while microbial biomass P was higher under blue lupin. Among plant species, the blue lupin rhizosphere exhibited higher acid and alkaline phosphatase activity as well as organic anion release. Soil P fractions were impacted by plant species but similar across CO2 treatments. Blue lupin accumulated labile organic P while depleted moderately labile organic P. Accumulation of labile organic P could be ascribed to microbial P immobilisation, whereas the mineralization of moderately labile organic P was associated with higher phosphatase activity. Wheat depleted acid extractable inorganic P the most, probably due to soil acidification and higher root biomass. These results suggest that plants can mobilise different P fractions irrespective of their chemical availability using morphological and/or physiological adaptations. However, these adaptations to acquire P from a low-P soil were not affected by eCO(2). This implies that current P fertiliser recommendations to boost or maintain crop production in low-P soils would remain unchanged under future eCO(2).

Automated summary

The experiment indicated that under P deficiency, plants did not show significant response to eCO2, and there were variations among different plant species.