Effect of Bacillus subtilis QST713 and Trichoderma asperellum T34 on P uptake by wheat and how it is modulated by soil properties

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Objectives The effect on P uptake by plants after inoculation with P-mobilizing 19 microorganisms may be modulated by soil properties, including natural microbiota. 20 However, to put this theory into practical use, research is needed to shed new light on the 21 soil factors which affect the capability of improving P nutrition in plants. The aim of this 22 study was to assess how two P-mobilizing microorganisms, Trichoderma asperellum T34 23 and Bacillus subtilis QST713, influence P uptake by wheat plants in different soils; this 24 will allow us to identify the soil properties which affect the efficiency of P nutrition in 25 plants. 26 Materials and methods. In a completely randomized experiment, wheat was grown in 12 pots in a growing chamber in soil with Olsen P values ranging from 4.8 to 8.7 mg kg-1 27 . 28 The plants were inoculated with 3 treatments: T34, B. subtilis and a non-inoculated 29 control. 30 Results and discussion. Overall, B. subtilis was more effective in increasing plant P 31 uptake and in mobilizing soil P (measured as Olsen P values) than T34. In some soils, B. 32 subtilis was the only treatment which increased Olsen P in the rhizosphere after 33 cultivation. However, the effect of both microorganisms differed depending on the soil. 34 For B. subtilis, phytase hydrolysable P, Olsen P, carbonates, the Feca/Fecbd ratio and citrate 35 soluble P accounted for 92 % of the variation in P uptake in inoculated plants (compared 36 with the non-inoculated control). Most of these soil properties also accounted for 87 % 37 of the variation in the levels of shoot DM in B. subtilis inoculated plants compared with 38 shoot DM in the control plants. In addition, Olsen P, the Feca/Fecbd ratio and phytase 39 hydrolysable P in the NaOH extracts accounted for 82 % and 74 % of the variation in the 40 effect of T34 on P uptake and shoot DM, respectively. Overall, the lower the initial Olsen 41 P in the soil, the higher the P uptake caused by microorganisms. 42 Conclusions. The initial availability of P and organic P in soil, in addition to other 43 properties affecting P dynamics in the soil, may explain the triggering and efficiency of 44 the P-mobilizing mechanisms in microorganisms. These are crucial in explaining the 45 potential benefits to crops and, as a result, their practical use as a bio-fertilizer.

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