Abstract
Previous experiments have shown that the application of fertilizer granules containing elemental sulfur (S0) as an ingredient (FBS0) in durum wheat crops produced a higher yield than that produced by conventional ones (F), provided that the soils of the experimental fields (F vs. FBS0) were of comparable quality and with the Olsen P content of the field’s soil above 8 mg kg−1. In this experiment the FBS0 treatment took place in soil with Olsen P at 7.8 mg kg−1, compared with the F treatment’s soil with Olsen P of 16.8 mg kg−1, aiming at reducing the imbalance in soil quality. To assess and evaluate the effect of FBS0 on the dynamics of the rhizospheric bacteria in relation to F, rhizospheric soil at various developmental stages of the crops was collected. The agronomic profile of the rhizospheric cultivable bacteria was characterized and monitored, in connection with the dynamics of phosphorus, iron, organic sulfur, and organic nitrogen, in both the rhizosoil and the aerial part of the plant during development. Both crops were characterized by a comparable dry mass accumulation per plant throughout development, while the yield of the FBS0 crop was 3.4% less compared to the F crop’s one. The FBS0 crop’s aerial part showed a transient higher P and Fe concentration, while its organic N and S concentrations followed the pattern of the F crop. The incorporation of S0 into the conventional fertilizer increased the percentage of arylsulfatase (ARS)-producing bacteria in the total bacterial population, suggesting an enhanced release of sulfate from the soil’s organic S pool, which the plant could readily utilize. The proportion of identified ARS-producing bacteria possessing these traits exhibited a maximum value before and after topdressing. Phylogenetic analysis of the 68 isolated ARS-producing bacterial strains revealed that the majority of the isolates belonged to the Pseudomonas genus. A large fraction also possessed phosphate solubilization, and/or siderophore production, and/or ureolytic traits, thus improving the crop’s P, Fe, S, and N balance. The aforementioned findings imply that the used FBS0 substantially improved the quality of the rhizosoil at the available phosphorus limiting level by modulating the abundance of the bacterial communities in the rhizosphere and effectively enhancing the microbially mediated nutrient mobilization towards improved plant nutritional dynamics.
Highlights
Plant nutrient acquisition from the soil via the root system is influenced by a wide range of factors
Despite the fact that the FBS0 crop was grown in soil containing 53% less phosphorus (Table 1), the dry mass accumulation per plant was statistically the same as the F crop’s one (Figure 2)
The FBS0 crop had a 3.4% lower yield (4.89 t ha−1 ) compared to the F crop (5.06 t ha−1 )
Summary
Plant nutrient acquisition from the soil via the root system is influenced by a wide range of factors. Plants 2019, 8, 379 microorganism communities, the fertilization regime, and environmental conditions are all factors of central agronomic importance. In this context, the biological activities of microorganisms can play an important role [1]. Regardless of the plant species, a fraction of the soil microbiome will eventually colonize the soil bordering the root surface (i.e., the rhizosphere), because plant roots release a wide range of compounds involved in attracting microorganisms, which may be beneficial, neutral, or detrimental to plants [2]. The PGPR that are involved in soil nutrients’ mobilization, enhancing the availability of the mobilized nutrients to the plant, are usually endowed with traits that stimulate the mobilization of unavailable plant nutrients through various mechanisms, including phosphate solubilization and production of siderophores, among several others
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