Effects of Bacillus subtilis and Pseudomonas fluorescens Inoculation on Attributes of the Lettuce (Lactuca sativa L.) Soil Rhizosphere Microbial Community: The Role of the Management System

Eirini Angelina,Efimia M. Papatheodorou,Nikolaos Monokrousos,Triantafyllia Demirtzoglou

doi:10.3390/agronomy10091428

Eirini Angelina, Efimia M. Papatheodorou + Show 2 more

Open Access

https://doi.org/10.3390/agronomy10091428

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Abstract

Inoculation with beneficial microbes has been proposed as an effective practice for the improvement of plant growth and soil health. Since soil acts as a physicochemical background for soil microbial communities, we hypothesized that its management will mediate the effects of microbial inoculants on the indigenous soil microbes. We examined the effects of bacterial inoculants [Bacillus subtilis (Ba), Pseudomonas fluorescens (Ps), and both (BaPs)] on the growth of Lactuca sativa cultivated in soils that originated from an organic maize (OS) and a conventional barley (CS) management system. Moreover, the biomass and the community structure of the rhizosphere microbial communities and the soil enzyme activities were recorded. The root weight was higher in CS than OS, while the foliage length was greater in OS than CS treatments. Only in OS pots, inoculants resulted in higher biomasses of bacteria, fungi, and actinomycetes compared to the control with the highest values being recorded in Ps and BaPs treated soils. Furthermore, different inoculants resulted in different communities in terms of structure mainly in OS soils. For soil enzymes, the effect of the management system was more important due to the high organic matter existing in OS soils. We suggest that for microbial inoculation to be effective it should be considered together with the management history of the soil.

Highlights

Several conventional farming management practices, such as extensive use of inorganic fertilizers and pesticides, have a significant impact on the environment [1,2]; increasing the greenhouse effect [3], reducing biodiversity [4], and enhancing toxicity in the food chain [5]
The experimental design consisted of two management systems [organically (OS) and conventionally (CS) managed soils] × four inoculation treatments [Bacillus subtilis (Ba), Pseudomonas fluorescens (Ps), Bacillus and Pseudomonas consortia (BaPs), and non-inoculated], with four replicates per treatment, giving a total of 32 pots arranged in a randomized block design
The management system exerted the only significant effect on plant growth and an independent significant effect on enzyme activity. It mediated the effects of inoculants on soil rhizosphere microbial biomass and community structure confirming partly our initial hypothesis

Summary

Introduction

Several conventional farming management practices, such as extensive use of inorganic fertilizers and pesticides, have a significant impact on the environment [1,2]; increasing the greenhouse effect [3], reducing biodiversity [4], and enhancing toxicity in the food chain [5]. Such practices could have serious impacts on the soil environment and on soil microbial communities. Organic farming practices, such as manure application and lack of tillage could improve soil fertility, increase microbial biomass [10] and activity [11], and elevate soil microbial diversity [12], affecting the soil microbial community structure [13].

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