Phosphatase activity and acidification in lupine and maize rhizosphere depend on phosphorus availability and root properties: Coupling zymography with planar optodes

Increase of phosphatase activity and rhizosphere acidification are two main physiological mechanisms of phosphorus mobilization by plants. To understand plant P-acquisition strategies, the spatial distribution of phosphatase activity and pH in the rhizosphere in response to P availability between legumes and cereals and along individual roots were investigated. Zymography of acid and alkaline phosphatase activities visualizing P hydrolysis potential was combined with planar optodes to localize pH changes in maize and lupine rhizosphere. Lupine was more adapted to P-deficiency than maize by increasing phosphatase activity (up to 30%), decreasing pH for 0.8 units in the rhizosphere and having larger hotspot areas compared to P addition. The P deficiency-induced increases of phosphatase activities and acidification were position-specific along taproot of lupine: acid phosphatase was highest while alkaline phosphatase was least at apical parts; pH was 1.7 units lower at the apical than at the basal part. The phosphatase activities and pH along lateral roots of lupine were independent on P availability but had specific distribution patterns: acid phosphatase activity declined from the root tips toward basal part, while the alkaline phosphatase activity was slightly increased from root tips; the pH was highest at the root tips (first 5 mm) and declined thereafter until stabilized after 20 mm. We conclude that 1) lupine is better adapted to P deficiency than maize by a stronger increase of phosphatase activities and facilitation of rhizosphere acidification; 2) The organic P mobilization by phosphatases and mineral P solubilization by acidification along individual mots were dependent on the root zone.

Automated summary

This study investigated the phosphatase activity and pH changes in the rhizosphere in response to P availability in legumes and cereals. It was found that lupine is better adapted to P deficiency than maize by increasing phosphatase activities and rhizosphere acidification. The spatial distribution of phosphatase activities and pH along individual roots of plants were found to be dependent on the root zone, with specific patterns observed in the distribution of acid and alkaline phosphatase activities along lateral roots of lupine.