Shoot δ¹⁵N and δ¹³C values of non-host Brassica rapa change when exposed to ±Glomus etunicatum inoculum and three levels of phosphorus and nitrogen

Abstract.

Glasshouse experiments were conducted to study the response of non-host Brassica rapa and host Sorghum bicolor to inoculation with the arbuscular mycorrhizal fungus (AMF) Glomus etunicatum when given different levels of N (0.9 mmol kg^–1 sand, 2.7 mmol kg^–1 sand, 8.1 mmol kg^–1 sand) and P (3.6 µmol kg^–1 sand, 10.7 µmol kg^–1 sand, 32.0 µmol kg^–1 sand) fertiliser. On both plant species, the presence of G. etunicatum inoculum (+AMF) was associated with significant changes of shoot δ¹⁵N values, with +AMF plants having larger average δ¹⁵N values than uninoculated plants (–AMF). These values are the largest average differences in shoot δ¹⁵N yet recorded for AMF and nutrient effects. B. rapa shoot δ¹⁵N average differences ranged from 1.67‰ to 2.70‰, while for S. bicolor they range between 2.07‰ and 4.40‰. For shoot δ¹³C only the non-host B. rapa responded to ±AMF and added N. Although the harvested dry weight biomass (–35.2% B. rapa; +39.8% S. bicolor) of both plant species responded to AMF inoculation, no direct relationship was observed between isotopic discrimination and growth inhibition for the non-host B. rapa. In this paper we discuss some implications regarding AMF inocula on the basis of our findings and current literature.