Microbial Consortia versus Single-Strain Inoculants: An Advantage in PGPM-Assisted Tomato Production?

Abstract

The use of biostimulants with plant growth-promoting properties, but without significant input of nutrients, is discussed as a strategy to increase stress resistance and nutrient use efficiency of crops. However, limited reproducibility under real production conditions remains a major challenge. The use of combination products based on microbial and non-microbial biostimulants or microbial consortia, with the aim to exploit complementary or synergistic interactions and increase the flexibility of responses under different environmental conditions, is discussed as a potential strategy to overcome this problem. This study aimed at comparing the efficiency of selected microbial single-strain inoculants with proven plant-growth promoting potential versus consortium products under real production conditions in large-scale tomato cultivation systems, exposed to different environmental challenges. In a protected greenhouse production system at Timisoara, Romania, with composted cow manure, guano, hair-, and feather-meals as major fertilizers, different fungal and bacterial single-strain inoculants, as well as microbial consortium products, showed very similar beneficial responses. Nursery performance, fruit setting, fruit size distribution, seasonal yield share, and cumulative yield (39–84% as compared to the control) were significantly improved over two growing periods. By contrast, superior performance of the microbial consortia products (MCPs) was recorded under more challenging environmental conditions in an open-field drip-fertigated tomato production system in the Negev desert, Israel with mineral fertilization on a high pH (7.9), low fertility, and sandy soil. This was reflected by improved phosphate (P) acquisition, a stimulation of vegetative shoot biomass production and increased final fruit yield under conditions of limited P supply. Moreover, MCP inoculation was associated with selective changes of the rhizosphere-bacterial community structure particularly with respect to Sphingobacteriia and Flavobacteria, reported as salinity indicators and drought stress protectants. Phosphate limitation reduced the diversity of bacterial populations at the root surface (rhizoplane) and this effect was reverted by MCP inoculation, reflecting the improved P status of the plants. The results support the hypothesis that the use of microbial consortia can increase the efficiency and reproducibility of BS-assisted strategies for crop production, particularly under challenging environmental conditions.

The role of N form supply for PGPM‐host plant interactions in maize

“…Accordingly, Nkebiwe et al (2016) reported increased root proliferation and plant growth promotion by PGPM inoculation combined with ammonium fertilization in maize, both, in laboratory and field experiments. Similar results were reported for P acquisition, plant growth promotion and yield formation of tomato in a drip-irrigated tomato production system with ammonium placement and inoculation of microbial consortia in the Negev desert in Israel (Bradá č ová et al, 2019). The results of Mpanga et al (2019) suggested that the beneficial effects of stabilized ammonium fertilization on PGPM per-formance might be at least partially attributed to an improved root-induced mobilization of P and other sparingly soluble nutrients by the well documented rhizosphere acidification effect of ammonium fertilizers (Neumann and Rö mheld, 2002).…”

“…Moreover, in agricultural systems, the amount (Dogra and Dudeja, 1993;Nouri et al, 2014;Huang et al, 2017;Schü tz et al, 2017) and the type of the applied fertilizers can also play an important role. In the latter context, the preferential perform-ance of PGPMs in combination with N-rich organic fertilizers has been repeatedly reported (Abbasi et al, 2015;Thonar et al, 2017;Mpanga et al, 2018;Bradá č ová et al, 2019). Recently, Mpanga et al (2019) found an improved plant performance associated with a wide range of fungal and bacterial PGPMs in combination with stabilized ammonium fertilizers as compared with nitrate fertilization.…”

“…Tab. 1 summarizes the effects in maize (Nkebiwe, 2016;Mpanga et al, 2019), wheat (Nkebiwe, 2016), and tomato (Mpanga et al, 2018;Bradá č ová et al, 2019). Accordingly, Nkebiwe et al (2016) reported increased root proliferation and plant growth promotion by PGPM inoculation combined with ammonium fertilization in maize, both, in laboratory and field experiments.…”

Improving the efficiency and effectiveness of global phosphorus use: focus on root and rhizosphere levels in the agronomic system

“…Certain production systems (e.g., tomato production systems based on nursery production in greenhouses with organic fertilizers and low fertility drip-fertigated field with mineral fertilizer in the Negev Desert) strongly respond to microbial inoculants with improved phosphate acquisition, quality and yield [43] . Beneficial effects of consortia inoculation vs single strains have also occasionally been observed, e.g., in a low fertile soil, where the soil microbial community is profoundly changed by inoculation of consortia [43] .…”

“…Certain production systems (e.g., tomato production systems based on nursery production in greenhouses with organic fertilizers and low fertility drip-fertigated field with mineral fertilizer in the Negev Desert) strongly respond to microbial inoculants with improved phosphate acquisition, quality and yield [43] . Beneficial effects of consortia inoculation vs single strains have also occasionally been observed, e.g., in a low fertile soil, where the soil microbial community is profoundly changed by inoculation of consortia [43] . Despite substantial rhizocompetence of inoculated microbes, these mostly represent a minor fraction of the soil microbiome after a few weeks, however, and community shifts toward less potentially pathogenic composition can persist beyond the prominent presence of inoculants [44] .…”