Inoculation with Aspergillus aculeatus Alters the Performance of Perennial Ryegrass under Phosphorus Deficiency

Phosphorus (P) is an essential nutrient element that is necessary for plant growth and development. However, most of the P exists in insoluble form. Aspergillus aculeatus has been reported to be able to solubilize insoluble forms of P. Here, to investigate the P-solubilizing effect of A. aculeatus on the performance of perennial ryegrass ( Lolium perenne ) under P-deficiency stress, we created four treatment groups: control [i.e., no Ca 3 (PO 4 ) 2 or A. aculeatus ], A. aculeatus only (F), Ca 3 (PO 4 ) 2 and Ca 3 (PO 4 ) 2 + A. aculeatus [Ca 3 (PO 4 ) 2 + F] treatment, and Ca 3 (PO 4 ) 2 at concentrations of 0 and 3 g per pot (0.5 kg substrate per pot). In our results, the liquid medium inoculated with A. aculeatus exhibited enhanced soluble P and organic acid content (tartaric acid, citric acid, and aminoacetic acid) accompanied with lower pH, compared with the noninoculated regimen. Furthermore, A. aculeatus also played a primary role in increasing the soluble P content of substrate (1 sawdust: 3 sand), the growth rate, turf quality, and photosynthetic capacity of the plant exposed to Ca 3 (PO 4 ) 2 + F treatment, compared with other groups. Finally, in perennial ryegrass leaves, there was a dramatic increase in the valine, serine, tyrosine, and proline contents, and a remarkable decline in the glutamic acid, succinic acid, citric acid, and fumaric acid contents in the Ca 3 (PO 4 ) 2 + F regimen, compared with other groups. Overall, our results suggested that A. aculeatus may play a crucial role in the process of solubilizing Ca 3 (PO 4 ) 2 and modulating perennial ryegrass growth under P-deficiency stress.