Deciphering Soil Microbial Dynamics in Northeastern American Grasslands with Goldenrods (Solidago sp.)

Abstract

Grasslands are important centers of biodiversity; however, these ecosystems have been in decline. Although many methods for grassland restoration have been developed, the abundant microbial communities in these regions are understudied and could be used to assist in these efforts. In this study, we aimed to understand how microbial communities varied by soil type, grassland site, and environmental conditions. Samples were taken from rhizosphere soil (attached to plant roots), proximal soil (close to the plant roots), and from bulk cores at Ricketts Glen State Park and Nescopeck State Park in northeastern Pennsylvania, USA, during June and August of 2021 and 2022. Rhizosphere soil samples were taken from the native common grassland plant, Solidago rugosa. 16S rRNA gene sequencing revealed that pH as well as soil type (bulk, proximal, or rhizosphere) significantly influenced the microbial community composition of each soil. Each soil type had its own distinct microbial communities, and proximal soil was identified as a transition zone between rhizosphere and bulk microbial communities. We also observed that the rhizosphere communities were dependent upon geography, as these communities were significantly different between grasslands even though the plant species remained the same. Our results highlight the complex nature of soil microbial communities and how many factors, including pH, soil type, and geography, can be overlayed to impact soil microbes. Results suggest future avenues of conservation research through modification and regulation of specific soil microbial communities in order to aid in the rehabilitation of these diminished regions.

Keywords: Grassland; Microbial ecology; Rhizosphere; Soil microbial communities.

Fig. 1

Microbial community taxonomy. A Microbial community taxonomy on the phylum level within soil types, “other” is bacteria that had a mean relative abundance under 4%. B Microbial community taxonomy on the order level within soil types, “other” is bacteria that has a mean relative abundance under 1.5%

Fig. 2

Box jitter plots of Shannon diversity. Box and jitter plot separated by soil type. The black line represents the mean Shannon diversity for each soil type

Fig. 3

Microbial community composition across soil types. Each color represents a different soil type. A All 120 soil samples. B Samples with a pH of 5 or higher. C Samples with a pH below 5

Fig. 4

Relative abundance of ASV303 and ASV110. A Bubble plot nMDS diagram of all 120 samples representing the abundance of ASV303. Larger dots indicate a higher abundance, and the smaller dots indicate a lower abundance. There is a higher abundance of ASV303 in the rhizosphere than in the bulk and proximal soil. B Bubble plot nMDS diagram of all 120 samples representing the abundance of ASV110. Larger dots indicate a higher abundance, and the smaller dots indicate a lower abundance. There is a higher abundance of ASV110 in the rhizosphere than in the bulk and proximal soil

Fig. 5

Relative abundance of ASV116 and ASV463. Bubble plot nMDS diagram representing the abundance of ASV116 and ASV463. Larger dots indicate a higher abundance, and the smaller dots indicate a lower abundance. A Indicator ASV116 in all 88 samples with a pH above 5. B Indicator ASV463 in all 32 samples with a pH below 5

Fig. 6

Relative abundance of ASV24 and ASV82. Bubble plot nMDS diagram represents the abundance of ASV24 and ASV82. The larger dots indicate a higher abundance, and the smaller dots indicate a lower abundance. A Indicator ASV24 in all 120 samples across both grasslands. B Indicator ASV82 in all 120 samples across both grasslands