Plant δ15N associated with arbuscular mycorrhization, drought and nitrogen deficiency

It has long been evident that plant delta(15)N chiefly reflects the processes which fractionate N-15/N-14 rather than the delta(15)N of plant N source(s). It has emerged recently that one of the most important fractionating processes contributing to the whole plant delta(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 N-15-depleted foliar delta(15)N, commonly as low as -12 parts per thousand. 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 N-15 by as much as 3.5 parts per thousand. 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 delta(15)N found in field situations and do so by N-15 enrichment rather than depletion. Copyright (C) 1999 John Wiley & Sons, Ltd.