Predominant Microbial Colonizers in the Root Endosphere and Rhizosphere of Turfgrass Systems: Pseudomonas veronii, Janthinobacterium lividum, and Pseudogymnoascus spp.

Qing Xia,Wei Shi,Thomas Rufty

doi:10.3389/fmicb.2021.643904

Abstract

Microbes can colonize plant roots to modulate plant health and environmental fitness. Thus, using microbes to improve plant adaptation to biotic and abiotic stresses will be promising to abate the heavy reliance of management systems on synthetic chemicals and limited resource. This is particularly important for turfgrass systems because intensive management for plant available nutrients (e.g., nitrogen), water, and pest control is necessary to maintain a healthy and aesthetic landscape. However, little is known on microbial species and host compatibility in turfgrass root endosphere and rhizosphere. Here, by using marker gene high throughput sequencing approaches we demonstrated that a few bacterial and fungal species prevailed the root endosphere and rhizosphere and were of a broad host spectrum. Irrespective of turfgrass species (bermudagrass, ultradwarf bermudagrass, creeping bentgrass, and tall fescue), defoliation intensities (i.e., mowing height and frequency), turfgrass sites, and sampling time, Pseudomonas veronii was predominant in the root endosphere, constituting ∼38% of the total bacterial community, which was much higher than its presence in the bulk soil (∼0.5%) and rhizosphere (∼4.6%). By contrast, Janthinobacterium lividum and fungal species of the genus Pseudogymnoascus were more abundant in the rhizosphere, constituting ∼15 and ∼ 39% of the total bacterial and fungal community, respectively, compared to their respective presence in the bulk soil (∼ 0.1 and 5%) and root endosphere (∼ 0.8 and 0.3%). Such stark contrasts in the microbiome composition between the root endosphere, rhizosphere, and bulk soil were little influenced by turfgrass species, suggesting the broad turfgrass host compatibility of these bacterial and fungal species. Further, their dominance in respective niches were mutually unaffected, implying the possibility of developing a multiple species formula for coping turfgrass with environmental stresses. These species were likely involved in controlling pests, such as infectious nematodes and fungi, decomposing root debris, and helping turfgrass water and nutrient uptake; yet these possibilities need to be further examined.

Highlights

Microbes inhabiting roots and rhizosphere can help plants to cope with biotic and abiotic stresses and thereby promote plant growth under adverse environmental conditions (Glick, 2012; Rolli et al, 2015; Timmusk et al, 2017)
All the four alpha diversity metrics were generally highest for the bulk soil, middle for the rhizosphere, and lowest for the root endosphere (Table 2)
Bacterial and fungal alpha diversity metrics in the root endosphere or rhizosphere were little associated with soil physicochemical properties or turfgrass system/sampling variables (Supplementary Figure 1), except for marginally significant correlations (P < 0.1) between some diversity metrics and turfgrass species/cultivars

Summary

Introduction

Microbes inhabiting roots and rhizosphere can help plants to cope with biotic and abiotic stresses and thereby promote plant growth under adverse environmental conditions (Glick, 2012; Rolli et al, 2015; Timmusk et al, 2017). Mechanisms by which microbes contribute to plant nutrient uptake, stress tolerance, and defense against pathogens are multifaceted and possible ones include, but not limited to controls on phytohormone production, reactive oxygen species scavenging, rhizophagy cycle, phosphorus solubilization, osmolytic adjustment, and antibiotic synthesis (Haas and Keel, 2003; Baca and Elmerich, 2007; Sandhya et al, 2010; Ansary et al, 2012; Alori et al, 2017; White et al, 2018) This has stimulated a great interest in developing microbial inoculant-based biotechnology for making managed systems more adaptive to environmental stresses as well as more ecologically friendly. Given the wide consensus that the plant-associated microbiome can shape the host fitness to the environment, we questioned what microbes in the turfgrass root endosphere and rhizosphere would be beneficial to sustainable turfgrass systems

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Discussion

Conclusion