Importance of phosphorus supply through endophytic <Emphasis Type="Italic">Metarhizium brunneum</Emphasis> for root:shoot allocation and root architecture in potato plants

Background and aims

Identification of organic P species is important to understand their origin, turnover in soils and their effects on soil fertility. Attention has been recently devoted to microbial inocula, referred to as Bioeffectors, that are capable to increase P bioavailability and plant uptake. Nevertheless, little is known on the effect of Bioeffectors on soil P forms and their dynamics in agricultural soils upon different P fertilization.

Methods

We investigated the effects of the application of different commercial inocula strains (Trichoderma harzianum T 22, Pseudomonas sp., and Bacillus amyloliquefaciens) alone or in combination with different P fertilizers (triple superphosphate, rock phosphate, and both composted cow- and horse-manure) on soil organic P forms. P forms were characterized by liquid-state ³¹P–NMR spectroscopy, while plant P uptake from P-treated soil was followed in a greenhouse pot experiment under maize cultivation.

Results

NMR spectra showed that the type of P fertilizer and bioeffectors inoculation, affected the abundance and the composition of organic P forms. The specific capacity of all bioeffectors, and especially Pseudomonas, was related to an increased content of diesters P forms. Pseudomonas, and, to a lesser extent, B. amyloliquefaciens showed the largest increase in combination with organic P amendments, which also provided the largest plant P uptake. This suggests a key role of Diester-P forms in determining P availability in agroecosystems.

Conclusions

Microbial inoculation plays an important role in the dynamics of soil P, inducing a rapid P cycling that prevents P fixation and losses from soils, thus enhancing the P fertilizer use efficiency in agricultural soils.