Arbuscular mycorrhizal fungi prefer to acquire ammonium from nutrient patches

Background/Question/Methods

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.

Results/Conclusions

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.