Mechanisms Involved in Soil–Plant Interactions in Response to Poultry Manure and Phytase Enzyme Compared to Inorganic Phosphorus Fertilizers

While soil responses to organic and inorganic phosphorus (P) fertilizers have been widely studied, plant physiological and molecular responses remain insufficiently characterized. Such an understanding is necessary to develop sustainable P fertilization strategies that enhance plant performance in soils with P limitations. This study investigated the impact of poultry manure (PM) and its combination with phytase enzyme on molecular plant responses involved in P use efficiency (PUE) of ryegrass plants growing on a P-deficient Andisol. A greenhouse experiment under controlled conditions was performed to evaluate soil properties, plant biomass, P uptake, plant performance, and the expression of P transporters under the following P treatments: P deficiency (PD), mineral fertilizers (F), PM alone, and PM combined with phytase. The combination of PM and phytase enhanced soil P availability by 60% and increased soil P enzyme activities 2.6-fold, facilitating the mineralization of organic P. This resulted in a 63% increase in shoot P concentration and a 35% enhancement in shoot biomass. Additionally, oxidative stress markers decreased, with lipid peroxidation in roots reduced up to five-fold, while antioxidant activity increased 1.6-fold. Molecular analysis revealed that the expression of the P transporter gene LpPHT1;4 was upregulated 9.3-fold, indicating an improved capacity for P acquisition and utilization. These findings suggest that phytase-mediated hydrolysis of organic P and the activation of plant P transporters are key mechanisms driving enhanced P uptake and efficiency in P-deficient soils.