Diversity And Community Structures Of Soil Fungi Associated With Different Ecotypes Of Switchgrass

Switchgrass (Panicum virgatum L.) is a perennial C4 grass native to North America. It has two typical ecotypes:the lowland ecotype, which grows bigger with coarse roots, and the upland ecotype, which is generally shorter with finer roots. Both upland and lowland ecotypes can grow on marginal lands unsuitable for crop production. Because of its high yield, drought and flooding tolerance, low herbicide and fertilizer requirements, ease of management, and strong adaptability to poor soil and climate conditions, switchgrass has been widely considered as an efficient bioenergy crop, a valuable forage plant and an important choice for soil conservation. Due to its economic and ecological significance, switchgrass has been introduced in China since 1980s, In the past decades, a great deal of studies have focused on conditions affecting its growth and productivity, as well as its adaptive strategies on marginal lands. Less is known about how switchgrass interacts with soil microorganisms which play potentially important roles in plant performance and productivity.This study aimed to investigate the differences in fungal communities associated with two different cultivars of switchgrass, "Kanlow" and "Pathfinder" representing lowland ecotype and highland ecotype, respectively. We were particularly interested in arbuscular mycorrhizal fungi (AMF) because of their symbiotic relationship with host plants and their functional significance in plant-soil interactions. We collected roots and rhizosphere soil samples under replicated plant individuals of Kanlow and Panthfinder that had been grown in a common garden for four years. We also collected bulk soil to serve as the control. To characterize general fungal communities in soils, we targeted the ITS2 region of fungal rDNA with Illumina sequencing. To characterize AMF communities in plant roots, we sequenced particle 18S rDNA in order to identify each constituent taxa. We also analyzed major nutrients of rhizosphere soil in order to relate fungal and AMF community variation with differences in soil properties.Based on the sequencing data of general fungi we obtained from all samples, a total of 636 operational taxonomic units (OTUs) were identified, mostly belonging to 35 fungal genera. Out of these OTUs,254,155, and 227 came from Kanlow, Pathfinder and bulk soils, respectively. Although 18% of the OTUs(115) were common in all samples,79 OTUs were unique to Kanlow,8 were unique to Pathfinder, and 60 were found in bulk soil only. Fungal species richness, community composition and diversity all differed among Kanlow, Pathfinder and bulk soils. Kanlow had the highest species richness and the most diverse fungal communities in rhizosphere.Switchgrass roots were heavily colonized by AMF. The colonization rates for all examined roots were greater than 92%, but there was no significant difference between the two ecotypes. AMF sequencing analyses identified a total of 10 OTUs belonging to 2 orders,2 families and 2 genera including Glomus and Paraglomus. The genus Glomus dominated the communities associated with both Kanlow and Pathfinder, whereas Paraglomus was only found in roots of Pathfinder ecotype whose AMF species richness was greater than Kanlow’s.Our soil analyses revealed that Panthfinder rhizosphere had significantly higher contents of available K. The contents of soil organic matter, total N and available P were also higher in Pathfinder rhizosphere, but not statistically significant. All these major nutrients except available P were low. This indicates that soil fungi, particularly AMF may play important roles in improving nutrient status of switchgrass that often grows well in nutrient poor soils. The relation between soil properties and fungal communities associated with different ecotypes of switchgrass needs to be further studied in order to understand the adaptive strategies of this economically and ecologically important plant.