Evaluation of the xylem ureide method for measuring N2 fixation in six tree legume species

摘要: Abstract The xylem ureide method, based on analysis of sap for N solutes associated with 2 fixation (ureides) and soil-N use (NO 3 − , α amino-N), is used estimating Pfix (proportion plant derived from fixation) herbaceous species the leguminous tribes Phaseoleae Desmodieae may have application tree legumes. We report experiments, involving Calliandra calothyrsus, Leucaena leucocephala, Gliricidia sepium, Sesania grandiflora, Desmodium rensonii Codariocalyx gyroides to: (i) determine each composition to calibrate, where possible, method using 15 isotope dilution as an independent measure Pfix; (ii) establish appropriate procedures sampling in field studies. In first experiment, legumes were grown 55–77 weeks sampled repeatedly (6–9 times) vacuum-extracted sap, shoot dry matter, total N. Asparagine was predominant amino compound all species. relative abundance ureide-N (ureide-N a proportion + amino-N NO N) compared five six Sap S. grandiflora could not be analysed ureides standard colorimetric methods because high levels non-specific, background colour. For D. C. ranged less than 20% (Pfix zero) around 65 40%, respectively 100%). Functions describing relationships between ( y ) x were: = 18.3 0.446 r 0.91) ; 8.49 0.279 0.92) . With other three species, related Pfix. concluded that technique suitable only. second established trees G. rensonii, calothyrsus assess protcols. Results indicated vacuum extraction should proceed immediately branch cut, plants need noon eliminate diurnal effects branch-to-branch variation values within single minor.