High-density planting of Panicum virgatum increases soil carbon sequestration and interacts with temporally dynamic soil and root microbiomes

Authors: KAZARINA, ANNA - Kansas State University; MANDYAM, KEERTHI - Alcorn State University; JUMPPONEN, ARI - Kansas State University; GIRISH, PANICKER K.S. - Alcorn State University; Tyler, Heather

Submitted to: Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2025
Publication Date: 10/31/2025
Citation: Kazarina, A., Mandyam, K., Jumpponen, A., Girish, P., Tyler, H.L. 2025. High-density planting of Panicum virgatum increases soil carbon sequestration and interacts with temporally dynamic soil and root microbiomes. Agriculture. https://doi.org/10.3390/agriculture15212274.
DOI: https://doi.org/10.3390/agriculture15212274

Interpretive Summary: Switchgrass is frequently used in conservation agriculture systems due to its ability to grow well in many geographic regions. The soil microbiome plays an important role in plant health and growth. As a result, there is an increasing interest in determining how the microbiome of switchgrass can be used in order to improve productivity. The microbiome can change rapidly based on conditions in the soil, which can have an effect on how the microbiome functions. However, there is limited information on how seasonal and plant development impact the soil microbiome in switchgrass. Scientists at Kansas State University, Alcorn State University, and the USDA-ARS Crop Production Systems Research Unit in Stoneville, MS evaluated how switchgrass variety and planting density influence soil chemistry and microbial community composition in roots and soil over time in a single growing season. Soil chemistry and microbial communities differed more between time points than they did between the type of switchgrass or how densely the switchgrass had been planted. The few differences that were observed between switchgrass treatments occurred earlier in the growing season. Analysis of community composition suggests that switchgrass varieties may differ in their disease susceptibility as well as their ability to recruit beneficial soil microbes early in the growing season. The results of this study may help guide the choice of variety in order to recruit microbiomes for optimal and sustainable switchgrass productivity.

Technical Abstract: Agricultural conservation management focuses on sustainable crop production while mitigating the environmental impacts of agronomic practices such as fertilization and tillage. Switchgrass (Panicum virgatum L.) has been championed for use in conservation agriculture due to its broad geographical distribution and high production on marginal or low-productivity agricultural lands. Because of its potential in conservation agriculture, there is increasing interest in understanding how to exploit the switchgrass microbiome to improve crop performance. The microbiome – including bacteria and fungi inhabiting rhizosphere soil and plant tissues – is important for switchgrass health and performance. However, information on how seasonal changes and plant growth stage impact the microbiome and its functionality is lacking. Here, we evaluated how four switchgrass varieties and two planting densities affect the soil chemistry and microbiomes under conservation agriculture conditions in southeast Mississippi. To also assess the temporal dynamics, we repeatedly sampled switchgrass roots and associated soils for a total of six times during one growing season, starting from within a week from the first leaf emergence in early spring to pre-frost in late fall. DNA was extracted and sequenced for bacterial (v4 of the 16S ribosomal RNA gene) and fungal (Internal Transcribed Spacer 2 (ITS2) of the ribosomal RNA repeat) metabarcode markers. We tested for variety, planting density, and temporal effects on switchgrass associated soil chemistry as well as on bacterial and fungal communities in roots and rhizosphere soil. Results indicated that the soil chemistry and the bacterial and fungal communities were temporally dynamic and shifted during the growing season. The effects of switchgrass varieties and their planting densities were minimal and mainly occurred early in the growing season - within the first few weeks since leaf emergence while density effects were even more rare across datasets. Indicator taxon analysis of early season compositional differences among the varieties identified putative pathogens and potential beneficial members of the microbiome, suggesting that varieties may differ in their disease susceptibility or ability to attract beneficial commensals or mutualists during the early growing season. Despite the overwhelming temporal dynamics, these data suggest that variety choices may enable optimization of the early microbiome assembly for minimal disease susceptibility and the support of sustainable switchgrass productivity. These data contribute towards a better understanding of interactions among plants and their associated microbiomes as well as their seasonal dynamics.