Rhizosphere Bacterial Communities Differ According to Fertilizer Regimes and Cabbage (Brassica oleracea var. capitata L.) Harvest Time, but Not Aphid Herbivory.

Flora J M O’Brien,Jeremy S Webb,Guy M Poppy,Marc G Dumont

doi:10.3389/fmicb.2018.01620

Flora J M O’Brien, Jeremy S Webb + Show 2 more

Open Access

https://doi.org/10.3389/fmicb.2018.01620

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Abstract

Rhizosphere microbial communities are known to be highly diverse and strongly dependent on various attributes of the host plant, such as species, nutritional status, and growth stage. High-throughput 16S rRNA gene amplicon sequencing has been used to characterize the rhizosphere bacterial community of many important crop species, but this is the first study to date to characterize the bacterial and archaeal community of Brassica oleracea var. capitata. The study also tested the response of the bacterial community to fertilizer type (organic or synthetic) and N dosage (high or low), in addition to plant age (9 or 12 weeks) and aphid (Myzus persicae) herbivory (present/absent). The impact of aboveground herbivory on belowground microbial communities has received little attention in the literature, and since the type (organic or mineral) and amount of fertilizer applications are known to affect M. percicae populations, these treatments were applied at agricultural rates to test for synergistic effects on the soil bacterial community. Fertilizer type and plant growth were found to result in significantly different rhizosphere bacterial communities, while there was no effect of aphid herbivory. Several operational taxonomic units were identified as varying significantly in abundance between the treatment groups and age cohorts. These included members of the S-oxidizing genus Thiobacillus, which was significantly more abundant in organically fertilized 12-week-old cabbages, and the N-fixing cyanobacteria Phormidium, which appeared to decline in synthetically fertilized soils relative to controls. These responses may be an effect of accumulating root-derived glucosinolates in the B. oleracea rhizosphere and increased N-availability, respectively.

Highlights

Healthy soils are vital for agricultural production and, an important pillar for achieving food security
Post hoc Tukey HSD tests showed that the control plants had a significantly lower fresh weight biomass than those treated with chicken manure (CM) (p = 0.0098), Low N (p < 0.0001), and High N (p < 0.0001)
Our results show that several operational taxonomic units (OTUs) assigned to the genus Flavobacterium increased in abundance in the rhizospheres of CM plants over time

Summary

Introduction

Healthy soils are vital for agricultural production and, an important pillar for achieving food security. Compositional shifts in these communities can have significant consequences for the nutritional status and health of crops. Modern farming practices, such as fertilizer applications, can alter soil microbial communities through their impact on various edaphic factors, including soil moisture, pH (Li et al, 2012; Tripathi et al, 2012; Blasiak et al, 2014), nutrient availability, organic matter content, and temperature (Kowalchuk and Stephen, 2001; Bulluck et al, 2002; Bates et al, 2011; de Vries et al, 2012b). In comparison to mineral fertilizers, organic fertilizers (e.g., animal manures and compost) have been reported to enhance the bacterial richness (number of species) and lower evenness (relative abundance of taxa) of soil communities (Hartmann et al, 2015; Lupatini et al, 2017). The amount of nitrogen (N) applied to soils has been reported to impact microbial communities (Nemergut et al, 2008; Ramirez et al, 2010, 2012; Fierer et al, 2012), leading to a reduction in soil microbial diversity in some cases (Li et al, 2016)

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