Vicia villosa is an annual legume plant,and is mainly used for green manure by farmers in southwest China.Field growth experiments were performed on six plots.The concentrations of mineral nutrients and soluble sugar,and the changes of carbon and nitrogen isotopic composition within and among organs of Vicia were determined.Significant differences in legume growth were found in response to soil type and its moisture conditions.The Vicia villosa was relatively well adapted to growth in limestone soils than sandstone soils.The distribution of sugar concentrations and δ13C-differences between roots and leaves indicate that the translocation of sugars from leaves to roots may be restricted by soil drought.Therefore,there was an inhibition of Pi distribution from roots to leaves,resulting in over optimum threshold of N/P ratio.Those may originate from the feedback regulation in the legume,where soluble sugar could not be distributed from leaves to roots.The results of δδ15N values in tissues suggest that there should be different preferential use of nitrogen resource by legume during the formation of nodules:before nodule formation the legume preferentially utilizes inorganic nitrogen from soils,but afterwards the nitrogen should be mainly from N2-fixation.Our results indicate that the lack of nodulation development,except for S2,should be ascribed to the factor controlling bi-direction nutrient transfer,which should be efficiency of establishment symbiosis with arbuscular mycorrhiza before nodulation formation.It is predicted that the species of Vicia villosa should be a legume associated with dual symbiosis with rhizobia and mycorrhiza.