title: Plant-fungus competition for nitrogen erases mycorrhizal growth benefits of Andropogon gerardii under limited nitrogen supply.
abstract: Considered to play an important role in plant mineral nutrition, arbuscular mycorrhizal (AM) symbiosis is a common relationship between the roots of a great majority of plant species and glomeromycotan fungi. Its effects on the plant host are highly context dependent, with the greatest benefits often observed in phosphorus (P)-limited environments. Mycorrhizal contribution to plant nitrogen (N) nutrition is probably less important under most conditions. Moreover, inasmuch as both plant and fungi require substantial quantities of N for their growth, competition for N could potentially reduce net mycorrhizal benefits to the plant under conditions of limited N supply. Further compounded by increased belowground carbon (C) drain, the mycorrhizal costs could outweigh the benefits under severe N limitation. Using a field AM fungal community or a laboratory culture of Rhizophagus irregularis as mycorrhizal inoculants, we tested the contribution of mycorrhizal symbiosis to the growth, C allocation, and mineral nutrition of Andropogon gerardii growing in a nutrient-poor substrate under variable N and P supplies. The plants unambiguously competed with the fungi for N when its supply was low, resulting in no or negative mycorrhizal growth and N-uptake responses under such conditions. The field AM fungal communities manifested their potential to improve plant P nutrition only upon N fertilization, whereas the R. irregularis slightly yet significantly increased P uptake of its plant host (but not the host's growth) even without N supply. Coincident with increasing levels of root colonization by the AM fungal structures, both inoculants invariably increased nutritional and growth benefits to the host with increasing N supply. This, in turn, resulted in relieving plant P deficiency, which was persistent in non-mycorrhizal plants across the entire range of nutrient supplies.
authors.affiliation: Laboratory of Fungal Biology Institute of Microbiology Czech Academy of Sciences Prague Czech Republic; Department of Mycorrhizal Symbioses Institute of Botany Czech Academy of Sciences Průhonice Czech Republic.
authors.forename: David
authors.initials: D
authors.lastname: Püschel
authors.affiliation: Laboratory of Fungal Biology Institute of Microbiology Czech Academy of Sciences Prague Czech Republic; Department of Mycorrhizal Symbioses Institute of Botany Czech Academy of Sciences Průhonice Czech Republic.
authors.forename: Martina
authors.initials: M
authors.lastname: Janoušková
authors.affiliation: Laboratory of Fungal Biology Institute of Microbiology Czech Academy of Sciences Prague Czech Republic.
authors.forename: Martina
authors.initials: M
authors.lastname: Hujslová
authors.affiliation: Laboratory of Fungal Biology Institute of Microbiology Czech Academy of Sciences Prague Czech Republic.
authors.forename: Renata
authors.initials: R
authors.lastname: Slavíková
authors.affiliation: Laboratory of Fungal Biology Institute of Microbiology Czech Academy of Sciences Prague Czech Republic.
authors.forename: Hana
authors.initials: H
authors.lastname: Gryndlerová
authors.affiliation: Laboratory of Fungal Biology Institute of Microbiology Czech Academy of Sciences Prague Czech Republic.
authors.forename: Jan
authors.initials: J
authors.lastname: Jansa
keywords: Arbuscular mycorrhizal fungi; belowground carbon drain; inoculation; mycorrhizal benefits and costs; nutrient uptake response; shoot nitrogen‐to‐phosphorus ratio