Arbuscular mycorrhizal fungi prefer to acquire ammonium from nutrient patches
Arbuscular mycorrhizal fungi (AMF) play a critical role in the global carbon cycle. Recent evidence suggests that AMF could also acquire a large amount of nitrogen (N) and this process is tightly coupled with AMF-mediated carbon cycling. We propose that AMF tend to proliferate in patches enriched with organic materials because of their high demand in ammonium. To test for this, we conducted a microcosm experiment with a combination of different AMF species and nutrient patches. We grew Triticum aestivum colonized with Gigaspora Margarita, Glomus Intraradices, Acaulospora scrobiculata, respectively, and then assessed the proliferation of AMF in 15N-labelled nutrient patches of nitrate, ammonium, amino acid and organic residues, separately.
We found that plants utilized both nitrate, ammonium, amino acids efficiently through AMF. Meanwhile, we found that AMF acquired ammonium-N preferentially over nitrate-N and amino acids. Meanwhile, a prominent proliferation of fungal hyphae in patches of decomposing organic residues was also observed. These findings highlight the importance of the form of nitrogen in understanding the mycorrhizal-mediation of N cycling in the N-limited terrestrial ecosystems.