Identifying the Microbial-mediated Strategies for Optimum Phosphorus Uptake in Bahiagrass and Rhizoma Peanut Mixture

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Commodities

• Agronomic: grass (misc. perennial), peanuts

Practices

• Crop Production: nutrient cycling, nutrient management

Rhizoma peanut (RP) [Arachis glabrata Benth.] is incorporated into grassland pastures, such as bahiagrass (BG) [Paspalum notatum Flüggé], to increase pasture feed quality and reduce the need for nitrogen (N) fertilizer inputs. Apart from N, phosphorus (P) is important for forage and animal nutrition. The nutrient dynamics of P is of interest because of its role in the contamination of water bodies. Soil P is influenced by management practices and crops and soil types. Applying P fertilizers to soils with high P sorption capacity, such as the Southern Coastal Plains, Ultisols, can render a large percent of the applied P inaccessible for plant uptake. Although forage species differ in their ability to solubilize soil P for uptake, there is also indication that bulk soil and rhizosphere-associated microorganisms differ across plant species, in terms of their impact on plant-available soil P. Soil microorganisms modify soil P sorption equilibria and increase inorganic P in soil solution through release of organic compounds and enzymes that solubilize P from soil minerals, while organic P is released through biological mineralization. Through P isotope labelling techniques, molecular and metatranscriptomic approaches, and microscopic imaging, this study aims to identify the impact soil microbial communities have for enhancing P availability in BG-RP mixed pastures compared to BG monoculture pastures. Locating and identifying specific microbial groups associated with soil P availability in pastures with and without a legume component, provides a means for evaluating the potential to enhance fertilizer P use efficiency through legume inclusion and related microbial functions.

Hypothesis

1. The integration of RP into BG system will enhance the community and functionality of both BG and RP associated microbial groups that are responsible for P solubilization and mineralization in microbial-soil interface and P exchange in plant-microbial interface.
2. The enhancement of microbial mediated P cycling in hypothesis 1 will be controlled by a set of P cycling genes (Table 1), including but not limited to the genes responsible for solubilizing inorganic P (e.g., gcd and PqqABCDEF), the genes responsible for mineralizing P (e.g. PhoADN, aphA, olpA, php, glp, and app, and the genes involved in microbial-P exchange and plant uptake at the microbial-root P interface.
3. Soil microbial P cycling processes (genes and enzymes release), especially the genes involved in P uptake and transport as well as P starvation genes, will be suppressed when P mineral fertilizers are applied.

Objectives

1. Determine the distribution of applied ³³P-labelled mineral P fertilizer on soil P pools, plant P uptake and P transfer under BG monoculture versus a BG-RP mixture.
2. Identify microbial communities in the different belowground plant parts of bahiagrass (root+rhizome), rhizoma peanut (roots+ rhizome+ nodules), and in the rhizosphere, in response to forage species composition with or without mineral P fertilizer.
3. Use qPCR to quantify organic P mineralization (e.g., phoC and bpp) and inorganic P dissolution (e.g., pqqC) genes in rhizosphere soil and bulk soil across forage species with and without P fertilizer.
4. Profile genome expression of root microbiomes (including AMF) and root cells, with emphasis on identifying and quantifying the expression of key genes that are involved in P uptake and transport, as well as P-exchange (and P-metabolism) in the different forage systems (monoculture vs mixture) with or without mineral P fertilizer.
5. Organize in-person visits with producers in North, Central, and South Florida and present our project findings to them.