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

View the project final report

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 a large percent of soil P is unavailable to plants, especially in weathered soils, and P play a critical role in the contamination of water bodies. This study investigated P uptake and mobilization strategies in BG monoculture versus BG-RP mixture under low and adequate soil P level. We also identified soil microbial communities responsible for nutrient uptake both in the field and in the greenhouse. We hypothesized that in addition to soil and plant root associated microbes, RP will employ strategies that will increase soil P availability in BG-RP mixture, especially under low soil-P. Our findings showed that under low soil P, RP in BG-RP mixture has the potential to increase BG shoot biomass compared to BG monoculture. Another interesting finding was that under low soil P, RP in BG-RP mixture had greater shoot concentration of P, Fe, Mn, Zn, and Cu concentrations than BG shoots under low P, indicating that RP has higher ability to mobilize these nutrients than BG. Soil-P fractions analysis showed that NaOH- organic P occupied a larger percent (34%) of soil P. Soil microbial analysis conducted on the field showed that RP enhanced the relative abundances of fungal genera Fusarium, Gibberella, and Humicola. These fungi contribute to litter decomposition and nutrient cycling through their saprophytic lifestyle.

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 effect of P fertilizer application 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.