Bacterial Subspecies Variation and Nematode Grazing Change P Dynamics in the Wheat Rhizosphere

Abstract

Low phosphorus soils are thought to constitute the majority of soils worldwide and cannot support intensive agriculture without high fertilizer inputs. Rhizobacteria are well-known to modify P dynamics and an increased bacterial diversity normally has a positive impact on various process rates. However, it is not known how variation in bacterial diversity at the subspecies level could influence trophic interactions in the rhizosphere and its consequences on plant P nutrition. We therefore hypothesized that the interactions between closely related P solubilizing bacteria and their grazing nematodes could improve plant P dynamics from an unavailable P source. We isolated four Pseudomonas poae strains and extracted nematodes from a Saskatchewan wheat field soil sample. The potential of all bacterial isolates with and without nematodes for increasing P availability in the wheat rhizosphere was tested in controlled microcosms with Ca3(PO4)2 as sole P source. Liberated P, phosphatase activity, plant P and bacterial abundance based on phnX gene copies were determined. Phosphorus solubilization efficiency of isolates varied between isolates whereas phosphatase enzyme activity was only detected under nematodes grazing and during the first 15 days of the experiment. Nematodes grazing upon individual Pseudomonas poae increased phosphatase enzyme activity, bacterial abundance, but decreased plant P concentration compared to non-grazed system. In contrast, the treatment combining all Pseudomonas poae isolates together with nematodes resulted in significant increases in P availability and plant P concentration. Diverse P-solubilizing efficiency and interaction with nematodes within the same bacterial “species” suggest that P dynamics might be linked to micro variation in soil diversity that would not accurately be picked up using common tools such as 16S rRNA gene sequencing.

Bacterial feeder Nematodes: Facilitator or competitor for Plant Phosphorus in soil

“…In addition, grazing might release P assimilated in bacterial biomass and making it more available to plant roots. (Irshad et al, 2011;Irshad et al, 2012Irshad et al, : 2018 claimed that the bacteria with their grazer nematodes have increased the availability of P from organic and inorganic sources in controlled conditions and our results could serve the extension of their findings in soil conditions. Richardson and Simpson, (2011) reported that the grazing activity upon PSB populations could be as efficient as the production of free P from insoluble mineral P. The treatments without TCP showed no difference or even negative effect of inoculation in case of root P which might be due to increased competition among plant roots, bacteria and nematodes without any added P resource.…”

“…Acid phosphatase activity (phosphomonoesterase) was analyzed by the method as modified by (Irshad and Yergeau, 2018). Briefly, the rhizoplane soil samples were incubated with p-nitrophenyl phosphate (p-NPP) as a substrate for enzyme activity for 1 hour.…”

“…Indeed, phosphatase activity, enhanced in the rhizosphere in response to P deficiency, has been observed in a wide variety of plant species (Richardson and Simpson, 2011). There is a positive correlation between phosphate-solubilization capacity and phosphatase activity (Irshad and Yergeau, 2018). Relwani et al, (2008) suggested that acid phosphatase plays a major role in P-solubilization, apart from other phosphate-solubilization mechanisms.…”

Isolation and Characterization of Phosphorus Solubilizing Bacteria With Multiple Phosphorus Sources Utilizing Capability and Their Potential for Lead Immobilization in Soil

“…Phospholipids and phytate are major organic P pool in soils, which can be hydrolyzed by phosphatase and phytase, respectively (Maougal et al, 2014;Neal et al, 2017;Irshad and Yergeau, 2018). Previous literatures have reported that alkaline phosphatase is exclusively originated from soil microorganisms, and acid phosphatase is mainly produced and secreted by plants (Krämer and Green, 2000;Fraser et al, 2015).Three prokaryotic genes, phoX, phoA, and phoD, are responsible for encoding alkaline phosphatase (Huang et al, 2009); three genes of bpp encoding β-propeller phytase, ptp encoding protein tyrosine phosphatase, and hap encoding histidine acid phosphatase are found in prokaryote (Lim et al, 2007;Neal et al, 2017).…”

Microbiological Insights into the Stress-Alleviating Property of an Endophytic Bacillus altitudinis WR10 in Wheat under Low-Phosphorus and High-Salinity Stresses

“…Among various abiotic stresses, salinity stress and phosphorus deficiency are two worldwide problems and restrict intensive agriculture [1,2]. As one of the major abiotic stresses, salinity affects crop production in arid and semiarid areas, which grow wheat as the major crop.…”