Department of Plant Sciences

Contribution of arbuscular mycorrhizal fungi (AMF) to P nutrition is evident in low-P soils, but such benefit may not be expected under non-limiting conditions. A trait to quantify responsiveness to AMF colonization is the mycorrhizal dependency (MD). Our objective was to compare the AMF colonization and MD in soybean, sunflower and maize under contrasting P levels. Synchronized soil and root field sampling allowed the characterization of the relationship between the available soil P and indigenous AMF colonization for the three species on several agricultural soils. A greenhouse experiment including different P levels and AMF inoculation was also conducted. For soybean and maize the AMF colonization was significantly and negatively correlated with available soil P following linear-plateau function, whereas for sunflower we could not find any significant relationship. The high colonization levels observed in the three species suggest that this mechanism is highly relevant for P nutrition of crops grown in the Pampean soils, even in P-rich soils, in which the percentage of AMF colonization did not fell below 30%. Soybean was the specie more favored from AMF colonization and this response was modulated by P availability. Mycorrhized soybean at low and medium P levels enhanced P uptake and total biomass and show the highest MD. Although maize showed low MD values across all P levels, none of them was negative, so there was not carbon drain in mycorrhized maize. Our results show that under contrasting growth conditions soybean had higher AMF colonization and MD than sunflower and maize.