The Non-Simultaneous Enhancement of Phosphorus Acquisition and Mobilization Respond to Enhanced Arbuscular Mycorrhization on Maize (Zea mays L.)

Arbuscular mycorrhizal (AM) fungi can ameliorate not only plant phosphorus (P) nutrition but also soil P mobilization, while P mobilization occurs secondarily and may in turn limit P acquisition at certain crop growth stages. It can be termed as the “mycorrhiza-inducible P limitation”, which has so far largely escaped study. A pot experiment was conducted to test the dynamic P acquisition of maize (Zea mays L.) at the vegetative growth stage and P mobilization in the soil in response to AM fungal inoculation in an unsterilized arable alkaline soil. The experiment included two fertilization levels and two AM inoculation levels, i.e., nitrogen (N), P, and potassium (K) fertilization (NPK) and non-fertilization (control), as well as Funneliformis mosseae inoculation (+M) and non-inoculation (–M). Regardless of fertilization, +M increased mycorrhizal colonization and plant biomass at weeks 4 and 8 but increased tissue P concentration only at week 4 compared with those of –M. In addition, the plant P acquisition and shoot biomass in the control+M treatment at weeks 4 and 8 were close to and much lower than those of NPK–M, respectively. Furthermore, the increase in soil P mobilization potential, which was achieved by the accelerated soil alkaline phosphatase activity and the decreased soil pH, was lower than the increase in root P-acquiring efficiency, which was achieved by the enhanced mycorrhization and ZEAma;Pht1;6 (a mycorrhiza- inducible Pi transporter in maize root) expression. Regardless of fertilization, +M thus significantly decreased soil available P concentrations compared with those in the –M treatments. Therefore, there was a large, real gap between soil P mobilization and root P acquisition in response to enhanced root mycorrhizal colonization, substantially limiting plant P acquisition and growth.