This study will assess N-fixation in rhizosheath forming and non-rhizosheath forming plants. For the first time. The quantity of nitrogen (N) rhizosheath forming plants obtain from either atmospheric or soil sources will be quantified 15N isotope dilution methods. The function of rhizosheath roots in hydraulic lift will also be measured. Rhizosheath soil may act as sinks for deep soil moisture supplies (hydraulic lift) or rhizosheath roots may act as barriers to moisture loss, which can have a direct effect on microbial activity within rhizosheaths and can significantly alter N-fixation. Research will determine whether hydraulic lift of moisture reserves from deep roots to rhizosheath soil occurs and whether hydraulic lift stimulates microbial numbers and N- fixation in rhizosheaths.
