Project Number: 8042-12000-039-00
Start Date: May 03, 2011
End Date: May 02, 2016
A. Eight Maryland soils were chosen that varied in pH, texture, organic C, and land use. After collection soils were sieved and maintained at field moisture levels at 4 °C. Soil water potential curves were determined. Soils were incubated in Mason jars under controlled conditions to systematically vary soil moisture, soil temperature, soil pH, soil texture, and amendments with organic amendments. Soil samples are analyzed for microbial community structure by terminal restriction fragment length polymorphism (TRFLP) and phospholipid fatty acid (PLFA) analysis. B. Using the same soils as in (A), a variety of crop and weed seeds will be planted in each soil in pots, using 1 plant species per pot in a full factorial of plant species x soil with 6 replicates. Crop plant species will include cucumber (Cucumis sativus) and wheat (Triticum aestivum), while weed species will include smooth pigweed (Amaranthus hybridus), and giant foxtail (Setaria faberi). Soil and rhizosphere samples will be analyzed by TRFLP, PLFA, and pyrosequencing. C. We have a collection of 20 air-dried soils, collected in Maryland, that vary in pH, soil texture, and land use. Cucumber seeds will be planted in each soil and seedlings grown to select soils that will support cucumber growth with minimal disease. A subset of 8 soils will be chosen that maximize variation in pH and texture. Cucumber seeds will be planted in pots filled with these soils with and without prior seed inoculation with the biocontrol agent Pseudomonas fluorescens Pf-5. Colony forming units (CFU) of an antibiotic (rifampicin) resistant mutant of Pf5 will be determined by dilution-plating onto selective media containing rifampicin. As the cucumber plants grow rhizosphere soil samples (six replicates per treatment) will be taken and used directly to determine the population density of Pf-5 and frozen at -20 °C for analysis of rhizosphere community structure by TRFLP, PLFA, and pyrosequencing. D. We are collaborating with ARS scientists in a variety of locations, including Beltsville, MD; Watkinsville, Georgia; Brookings, South Dakota; Morris, MN; Prosser, WA; and Urbana, IL. They are using rye and/or vetch cover crops as part of their management systems. Bulk soil samples (0-15 cm depth) from three to four replicate plots, with treatments including rye, vetch, and bare soil, are being sent to us twice annually ( spring and fall) and being stored at -20 °C. Soil microbial community structure will be analyzed by TRFLP for Eubacteria, Archaea, and fungi, while soil enzyme assays will be used to measure community function.