Plant δ15N associated with arbuscular mycorrhization, drought and nitrogen deficiency

It has long been evident that plant 15 N chiefly reflects the processes which fractionate 15 N/ 14 N rather than the 15 N of plant N source(s). It has emerged recently that one of the most important fractionating processes contributing to the whole plant 15 N is the presence/absence, type or species of mycorrhiza, especially when interacting with nutrient deficiency. Ecto- and ericoid mycorrhizas are frequently associated with 15 Ndepleted foliar 15 N, commonly as low as ˇ12%. As shown by the present study, plants having no mycorrhiza, or those infected with various species of arbuscular mycorrhiza (AM)-forming fungi, interact with varying concentrations of soil nitrogen [N] and moisture to enrich plant 15 N by as much as 3.5%. Hence the lack of a mycorrhiza, or variation in the species of AM-forming fungal associations, can account for about 25% of the usually reported variations of foliar 15 N found in field situations and do so by 15 N enrichment rather than depletion. Copyright # 1999 John Wiley & Sons, Ltd.