The proposed purchase of a mass spectrometer for isotope ratio analyses is to benefit and enhance a number of collaborative projects, especially those of the rhizosphere research group of which the principal investigator are major participants. The objectives of this research group are: (1) to understand the fundamental relationships among plant roots, soil, and microorganisms (rhizosphere systems), (2) to characterize and quantify nutrients cycling in rhizosphere systems of natural and disturbed ecosystems (ecosystem rhizosphere), and (3) to provide, through a multidisciplinary approach, information derived from rhizosphere studies for use in improving the nutrient use efficiency of plants and managing environmentally sensitive ecosystems in response to their reactions to human influence. A considerable amount of research has already been conducted or been initiated by our research group, and several more projects are being considered. A significant portion of the methodology being developed is centered around the use of a stable isotope of nitrogen (15N), a major nutrient common to all rhizosphere systems. The 15N isotope can be traced throughout the plant-soil system using the isotope-ratio mass spectrometer for analysis. The ability to trace this element through the various transformation processes affords us the opportunity to quantify the processes of rhizosphere systems with emphasis on microorganisms-root interactions and nutrient transport and transformations. Our cooperative projects address basic questions on the functions of rhizosphere systems of which is a dire lack of knowledge. These areas include the effect of introduced organisms in the rhizosphere on plant-soil nutrient dynamics, nitrogen cycling in deforested areas, nitrogen use efficiency in semi-arid areas, rhizosphere processes, and the fate of genetically engineered organisms in the environment. These projects will contribute significantly to our basic knowledge of rhizosphere functioning. The acquisition of a modern isotope-ratio mass spectrometer will greatly enhance our ability to carry out the planned research as well as to stimulate other research interests.
