Mycorrhizae on Roots of Quercus havardii Growing in Habitat and Non-habitat Soils

Le, Phuong Ngoc Minh
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Quercus havardii, commonly known as sand shinnery oak, is a deciduous shrub that primarily grows on deep sandy soils ranging from northern Texas and western Oklahoma southward into the Chihuahuan Desert. Sand shinnery oak has an immense root system, consisting of taproots and lateral roots. The root system allows them to withstand droughts and dry weather conditions. The continuous ground cover of sand shinnery oak is useful in preventing soil erosion and can act as a food source for livestock and wild animals after its flowering period. Recent demands of the oil fracking industry for sand has led to the mining of sandy patches in sand shinnery oak habitat. Destruction of sand shinnery oak cover to excavate and remove sand from the environment has resulted in bare patches that are prone to erosion, and consequently increased the need for soil immobilization and potential restoration. Restoration with nursery-grown plantlets of sand shinnery oak have been considered; however, they require feasibility studies that highlight basic growth requirements and conditions for this plant, which is adapted to the dry and nutrient-deficient conditions in its habitat. The goal of this study was to assess the potential interaction of sand shinnery oak with microbes known to be beneficial in the acquisition of both water and nutrients, i.e. mycorrhizal fungi. To better assess the potential interactions between sand shinnery oak and potential fungal symbionts, three studies were conducted: (1) mesocosms were setup and established with two soils, i.e. with habitat sandy soil for sand shinnery oak from West Texas, and with non-habitat sandy from Bastrop, Texas, in a factorial design with soil type, and presence/absence of sand shinnery oak and phosphate fertilization as variables; (2) fungi were cultured and identified from both soils and the mesocosms; (3) bulk soils and rhizospheres (where applicable) were analyzed for fungal diversity by Next Generation Sequencing (NGS) using the Illumina MiSeq. Thirty isolates were obtained from all treatments and identified by Sanger sequencing of rRNA gene ITS regions with primer sets ITS1F/ITS2 and NS3/NS6, with only two isolates (Marianna sp. and Fusarium sp.) also found by NGS using the Illumina MiSeq, indicating the inadequacy of growth-dependent analyses procedures for fungal diversity in soils. NGS data showed that fungi in habitat soil from West Texas soil was slightly less diverse compared to non-habitat soil from Bastrop, with 12 and 13 individual reads retrieved, respectively, contradicting assumptions of higher diversity as a function of plant-microbe interactions benefiting the development of sand shinnery oak in its habitat. Four reads were commonly found in mesocosms of both habitat and non-habitat mesocosms, representing Pezzia sp., Fusarium keratoplasticum, Rhodotorula sp. and Xenoacremonium recifer, respectively. Depending on the treatment, additional reads representing Cladosporium sp. and Alternaria sp. might be present but restricted to specific treatments (e.g. absence of phosphate amendment). The fungal composition in non-habitat soil for sand shinnery oak (Bastrop) was significantly affected by the presence/absence of phosphate fertilization, and also by the presence/absence of plants. These effects were less pronounced in mesocosms with habitat soils from West Texas. In contrast to non-habitat soils, habitat soils were dominated by an uncultured fungus with highest sequence similarity to Sebina species, that are known mycorrhizae forming symbiotic relationships with trees and orchids. While the uncultured fungus represented by read 3 represented a major component of the fungal community in treatments with or without plants when amended with phosphate, all other reads obtained were restricted to mesocosms without direct effect of plants, i.e. the rhizosphere. These results indicate differences in diversity of fungi in habitat and non-habitat soils, and show potential effects of plants and phosphate fertilization on the composition of the fungal community. These statements are based on analyses of the most abundant reads only (i.e. those exceeding 1% of the abundance of all reads), overall diversity, including indications on the potential presence of mycorrhizae, might have been underestimated by our choice of the analyses cutoff at 1% abundance. Sequences in lower abundance could still represent signature fungi for soils and treatments that might have been overlooked due to our threshold setting. Thus, analyses of individual reads found below our threshold might provide additional data on differences in fungal community structure in habitat and non-habitat soils, affected by sand shinnery oak and/or phosphate treatments. Still, the potential presence of mycorrhizae in habitat soils might provide additional challenges but also opportunities for restoration of excavated sites with nursery-grown sand shinnery oak, and potentially increase the likelihood of re-establishment of sand shinnery oak on these sites.
Mycorrhizae, Mycorrhizal fungi, Quercus havardii, Sand Shinnery Oak, Illumina Sequencing, Sanger Sequencing
Le, P. N. M. (2019). <i>Mycorrhizae on roots of Quercus havardii growing in habitat and non-habitat soils</i> (Unpublished thesis). Texas State University, San Marcos, Texas.