Abstract
Phosphorus (P) is an essential nutrient for plants. The use of plant growth-promoting bacteria (PGPB) may also improve plant development and enhance nutrient availability, thus providing a promising alternative or supplement to chemical fertilizers. This study aimed to evaluate the effectiveness of Enterobacter sp. strain 15S in improving the growth and P acquisition of maize (monocot) and cucumber (dicot) plants under P-deficient hydroponic conditions, either by itself or by solubilizing an external source of inorganic phosphate (Pi) [Ca3(PO4)2]. The inoculation with Enterobacter 15S elicited different effects on the root architecture and biomass of cucumber and maize depending on the P supply. Under sufficient P, the bacterium induced a positive effect on the whole root system architecture of both plants. However, under P deficiency, the bacterium in combination with Ca3(PO4)2 induced a more remarkable effect on cucumber, while the bacterium alone was better in improving the root system of maize compared to non-inoculated plants. In P-deficient plants, bacterial inoculation also led to a chlorophyll content [soil-plant analysis development (SPAD) index] like that in P-sufficient plants (p < 0.05). Regarding P nutrition, the ionomic analysis indicated that inoculation with Enterobacter 15S increased the allocation of P in roots (+31%) and shoots (+53%) of cucumber plants grown in a P-free nutrient solution (NS) supplemented with the external insoluble phosphate, whereas maize plants inoculated with the bacterium alone showed a higher content of P only in roots (36%) but not in shoots. Furthermore, in P-deficient cucumber plants, all Pi transporter genes (CsPT1.3, CsPT1.4, CsPT1.9, and Cucsa383630.1) were upregulated by the bacterium inoculation, whereas, in P-deficient maize plants, the expression of ZmPT1 and ZmPT5 was downregulated by the bacterial inoculation. Taken together, these results suggest that, in its interaction with P-deficient cucumber plants, Enterobacter strain 15S might have solubilized the Ca3(PO4)2 to help the plants overcome P deficiency, while the association of maize plants with the bacterium might have triggered a different mechanism affecting plant metabolism. Thus, the mechanisms by which Enterobacter 15S improves plant growth and P nutrition are dependent on crop and nutrient status.
Highlights
Crops cultivated around the world, belonging to both monocot and dicot clades, can be very diverse; their growth and development are strongly influenced by the state and the availability of nutrients in the soil
P-deficient cucumber plants appeared darker in color (Figure 2) with the supplemented with 0.1 mM of KH2PO4; P, nutrient solution (NS) non-supplemented with KH2PO4) and four biostimulant treatments [C, uninoculated control; CIP, uninoculated control with the insoluble phosphate Ca3(PO4)2; 15S, inoculated with the plant growth-promoting bacteria (PGPB) Enterobacter 15S; 15S in combination with the insoluble phosphate (15SIP), inoculated with the PGPB Enterobacter 15S plus the insoluble phosphate Ca3(PO4)2]
No significant differences are indicated by omitting notation letters. asoil-plant analysis development (SPAD), SPAD units; Length, total root length; Surf. area, root surface area; Diameter, root diameter; Volume, total root volume; Tips, Number of root tips; RDW, root dry weight; SDW, shoot dry weight; R/S, root-to-shoot ratio. bP levels: P+ [nutrient solution (NS) supplemented with 0.1 mM of KH2PO4]; P– (NS non-supplemented with KH2PO4). cBiostimulant treatments: C, uninoculated control; CIP, uninoculated control with the insoluble phosphate Ca3(PO4)2; 15S, inoculated treatment with the PGPB Enterobacter 15S; 15SIP, inoculated treatment with the PGPB Enterobacter 15S plus the insoluble phosphate Ca3(PO4)2
Summary
Crops cultivated around the world, belonging to both monocot and dicot clades, can be very diverse; their growth and development are strongly influenced by the state and the availability of nutrients in the soil. The yield levels and the overall performance of a crop can considerably vary both spatially and temporally, depending on both soil characteristics and agricultural practices In this context, phosphorus (P) is known to play a crucial role in plant nutrition; helping to achieve optimal growth and productivity. Plants take up P as inorganic phosphate (Pi); due to its low solubility and mobility, P is sparingly available in the soil solution, as its concentration is often rather limited (
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