Interaction between Grasses and Epichloë Endophytes and Its Significance to Biotic and Abiotic Stress Tolerance and the Rhizosphere.

Cool-season grasses are the most common forage types in livestock operations and amenities. Several of the cool-season grasses establish mutualistic associations with an endophytic fungus of the Epichloë genus. The grasses and endophytic fungi have evolved over a long period of time to form host-fungus specific relationships that confer protection for the grass against various stressors in exchange for housing and nutrients to the fungus. This review provides an overview of the mechanisms by which Epichloë endophytes and grasses interact, including molecular pathways for secondary metabolite production. It also outlines specific mechanisms by which the endophyte helps protect the plant from various abiotic and biotic stressors. Finally, the review provides information on how Epichloë infection of grass and stressors affect the rhizosphere environment of the plant.

Influence of Tall Fescue Epichloë Endophytes on Rhizosphere Soil Microbiome.

Tall fescue (Lolium arundinaceum (Schreb.) S.J. Darbyshire) often forms a symbiotic relationship with fungal endophytes (Epichloë coenophiala), which provides increased plant performance and greater tolerance to environmental stress compared to endophyte-free tall fescue. Whether this enhanced performance of tall fescue exclusively results from the grass-fungus symbiosis, or this symbiosis additionally results in the recruitment of soil microbes in the rhizosphere that in turn promote plant growth, remain a question. We investigated the soil bacterial and fungal community composition in iron-rich soil in the southeastern USA, and possible community shifts in soil microbial populations based on endophyte infection in tall fescue by analyzing the 16s rRNA gene and ITS specific region. Our data revealed that plant-available phosphorus (P) was significantly (p < 0.05) influenced by endophyte infection in tall fescue. While the prominent soil bacterial phyla were similar, a clear fungal community shift was observed between endophyte-infected (E+) and endophyte-free (E-) tall fescue soil at the phylum level. Moreover, compared to E- soil, E+ soil showed a greater fungal diversity at the genus level. Our results, thus, indicate a possible three-way interaction between tall fescue, fungal endophyte, and soil fungal communities resulting in improved tall fescue performance.

Current Progress in Nitrogen Fixing Plants and Microbiome Research.

In agroecosystems, nitrogen is one of the major nutrients limiting plant growth. To meet the increased nitrogen demand in agriculture, synthetic fertilizers have been used extensively in the latter part of the twentieth century, which have led to environmental challenges such as nitrate pollution. Biological nitrogen fixation (BNF) in plants is an essential mechanism for sustainable agricultural production and healthy ecosystem functioning. BNF by legumes and associative, endosymbiotic, and endophytic nitrogen fixation in non-legumes play major roles in reducing the use of synthetic nitrogen fertilizer in agriculture, increased plant nutrient content, and soil health reclamation. This review discusses the process of nitrogen-fixation in plants, nodule formation, the genes involved in plant-rhizobia interaction, and nitrogen-fixing legume and non-legume plants. This review also elaborates on current research efforts involved in transferring nitrogen-fixing mechanisms from legumes to non-legumes, especially to economically important crops such as rice, maize, and wheat at the molecular level and relevant other techniques involving the manipulation of soil microbiome for plant benefits in the non-legume root environment.

Spatial Distribution of Inorganic Nitrogen in Pastures as Affected by Management, Landscape, and Cattle Locus.

Uneven spatial distribution of soil N in conventionally managed pastures is a function of various biotic and abiotic factors and results in poor land use efficiency. In this study, we measured soil inorganic N (at depths of 0-5, 5-10, and 10-20 cm) in a 50-m grid and specific areas of interest from eight conventionally managed beef pastures (∼17 ha each), four near Eatonton and four near Watkinsville in the southern Piedmont of Georgia, USA, to assess the effects of management, landscape, and cattle locus in spatial distribution of soil inorganic N. Significant spatial autocorrelation was observed in the soil inorganic N indicating that the regions of high inorganic N deposition were near (within 91 m of) one or more pasture equipage (hay, shade, and water). In the Watkinsville pastures, inorganic N was 65% higher within 5 m of shade than the rest of the pastures, down to a 10-cm soil depth. In the Eatonton pastures, inorganic N (0-5 cm) was 22% higher within 30 m of a hay-feeding areas than the rest of the pasture. Cattle locus calculated as cattle density (cow ha yr) was a function of pasture equipage and had a significant positive relationship with soil inorganic N. Landscape parameters (slope and elevation) significantly affected inorganic N distribution; however, the effect was small and was masked by management factors. Our results suggest that strategic placement of pasture equipage (hay, shade, and water) can effectively distribute N where needed in beef pastures, thereby increasing land use efficiency.