Isotopic discrimination associated with symbiotic nitrogen fixation in stylo (Stylosanthes hamata L.) and cowpea (Vigna unguiculata L.)

Abstract

A glasshouse study was carried out to determine the isotopicdiscrimination (B values) and the isotopic fractionation factors (β)associated with symbiotic nitrogen fixation in stylo (Stylosantheshamata L.) and cowpea (Vigna unguiculata L.Walp). The B values are required to improve the accuracy of estimates ofnitrogen fixation based on the differences in the natural abundance of15N between nitrogen fixing and non-fixing plants. The B values ofplants grown in nitrogen free media for stylo were −1.60, 82 days after planting (DAP) and −1.86, 98 DAP and −1.48, 49DAP and −1.51 for cowpea shoots 73 DAP. Theisotopic fractionation factors for stylo and cowpea were 1.0016, 82DAP and 1.0019, 98 DAP and 1.0018, 49 DAPand 1.0015, 73 DAP, respectively.