Influences of phosphorus application level on maize arbuscular mycorrhizal colonization and hyphal acquisition to heterogeneous phosphorus supply

Objectives The objectives of this study are to investigate the arbuscular mycorrhizal infection on maize and their promotion to plant phosphorus uptake in acid soils, and to study the effects of arbuscular mycorrhizal fungi and environmental phosphorus nutrition on the acquisition of local phosphorus nutrition by root hyphae.

Methods Using pot experiment and maize as host plant, three P levels of 0, 50 and 500 mg/kg (P0, P50 and P500, P was supplied by KH₂PO₄) were designed. Then two plastic chambers containing 120 g sterilized soil with P 50 mg/kg were installed in each pot. One chamber was enclosed with 0.45 μm mesh fabric to prevent hyphae and root from penetration (–H treatment), and the other one was enclosed with 50 μm mesh fabric to allow hyphae penetration (+H treatment). Maize plant growth, P uptake, AM fungi colonization, hyphal density and P acquisition by hyphae from chambers were measured.

Results The plant height, leaf SPAD value, total dry weight, P concentration and uptake were all increased with the increase of P supply level, with the highest root dry weight in P50 treatment, while root/shoot ratio was decreased with the increase of P level. The P50 treatment showed the best AM fungi colonization rate and development of arbuscule and vesicle. Compared with the P50 treatment, the P0 treatment had fewer vesicles although there was no significant difference in the AM colonization rate and arbuscule richness. Even with 87.22% colonization point existing in whole root system, plants of the P500 treatment showed the lowest AM fungi colonization rate and development of arbuscule and vesicle, indicating severe inhibition of high P supply on AM fungi. The bulk soil hyphal density was decreased with the increase of soil P level, with a little difference between the P0 and P50 treatments. The hyphal density kept stable and was very low in all –H chambers, while the hyphal density in the +H chambers was decreased with the increase of bulk soil P level. Under the same P application level, the hyphal density was highest in bulk soil, followed by +H chamber soil, and lowest in –H chamber soil. The P acquisition from the +H chamber by hyphae was decreased with increase of bulk soil P supply.

Conclusions A moderate soil P supply could benefit root growth and AM fungi colonization in acid soil. The hyphae exploration for local P supply is influenced by bulk soil P status, with higher P acquisition from P-rich area when bulk soil P supply is low.