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Are Rhizobium populations in clover affected by organic management?

Rhizobia are vital in the fixation of nitrogen in legumes. Legumes are extensively used in organic farming systems for fertility building, so this project will determine whether there is a difference in the diversity of Rhizobia in organic compared to non-organic white clover.

Department: Agricultural & Food Economics, Agriculture, Policy and Development

Supervised by: Dr Hannah Jones

The Placement Project

Legume species have the capacity to fix atmospheric nitrogen through the symbiotic association with Rhizobia bacteria in their roots. There are five recognised Rhizobia genera: Rhizobium, Sinorhizobium, Bradyrhizobium, Azorhizobium and Mesorhizobium. A wide variation in host-Rhizobia combinations have been observed although there is some specificity in the association for some plant species (e.g. Moreira et al., 1998). The ability of the plant to obtain organic nitrogen from the bacteria is of major economic value in agricultural rotations for the (1) production of grain legumes; and (2) building soil fertility. However, there is limited knowledge relating to the diversity of Rhizobia bacteria in agricultural soils in the UK and how management practices influence the soil populations. The population level and the diversity of Rhizobia species in the soil has been shown to be influenced by the previous cropping (Miethling et al, 2000) and the use of agrochemicals (e.g Afifi et al, 1969). Therefore, we hypothesise that the diversity and the number of Rhizobia will be greater in organic compared to non-organic managed soils because of the prohibition of agrochemical use on certified land, and as a result of the standard use of legumes in organic rotation (Watson et al, 2002), To test this hypothesis the student will sample the bacterial nodules from white clover (Trifolium repens) grown under organic and non organic conditions. The clover will be grown and harvested from the University of Reading Sonning research station where adjacent organic and non-organically managed plots will reduce the variability of soil type, and climate on bacterial diversity. Bacteria will be extracted from root nodules from plants sampled from the two treatments. A phylogenetic analysis will be carried out on (1) the diversity of bacteria within one plant; and (2) the diversity of bacteria between plants sampled within the same treatment. Phylogenetic analysis will be carried out using RFLP analysis of the SSU rDNA integenic spacer, and of five parts of the conserved symbiotic region adjacent to the nod gene (Lafay & Burdon, 1998). Taken together, these analyses will provide key information on the importance of using organic and non-organic farming on bacterial diversity and plant growth.

Tasks

The student will spend the majority (>90%) of their time carrying out experiments in a laboratory. Weeks 1-2 plant sampling and Rhizobium extraction Weeks 3-6: DNA extraction & sequencing Weeks 7-9 Phylogenetic analysis Week 10 Project completion

Skills, knowledge and experience required

Essential: an interest in microbiology and agricultural production systems, and good teamwork skills. Desirable: some basic lab skills such as culturing bacteria and making solutions; growth of plants; able to use a microscope.

Skills which will be developed during the placement

The student will learn how to culture bacteria; perform molecular biology including the polymerase chain reaction and RFLP, and use phylogenetic assessment software. When a paper is written from this work, the student would certainly be either 1st or 2nd author. The PI’s lab will learn from Dr Jones the details regarding agricultural rotation and farm management.

Place of Work

Sonning Field Station & AMS Wing laboratory G53

Hours of Work

Monday-Friday 9am-5pm

Approximate Start and End Dates (not fixed)

Unknown - Unknown

How to Apply

Students should send a covering letter and curriculum vitae to h.e.jones@reading.ac.uk


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