Phosphate fertilization of grassland columns affects the soil microbiota while plant growth rates stay unchanged

This study evaluates the effect of phosphate fertilization on soil biota and soil biological phosphorus (P) cycling in grasslands. Soil columns were setup in a greenhouse using a P-limited Irish soil (index 1), planted with Lolium perenne and fertilized with 0 (control), 5 (low), 10 (medium) and 20 (high) kg/ha inorganic phosphate P. Weekly measurements at different soil depths identified only traces of phosphate in soil solution for the duration of 14 weeks, even after phosphate fertilization. Grass dry matter yield between treatments was not significantly different. High phosphate fertilization significantly reduced the arbuscular mycorrhization (AM) rate, bacterial- and fungal-feeding nematode population, bacterial phoD gene abundance, but increased alkaline and acid phosphatase activities. Likewise, high and medium P treatments significantly shifted the bacterial, fungal and AM community structures compared to the control. Furthermore, the control had a significantly higher abundance of certain bacterial genera when compared to the high phosphate treatment (e.g. Bacillus, Bradyrhizobium, Paenibacillus, Nocardioides, Balneimonas, Allicyclobacillus) that have been associated with P mobilization in the past. These results suggest that a positive effect of a single inorganic phosphate application on plant growth in a soil is largely cancelled out by its negative effect on the soil microbiotas. These findings support the hypothesis that soil microbiotas play an important role in plant P supply in P-limited soils.