Arbuscular mycorrhiza improved phosphorus efficiency in paddy fields

• We tested the role of arbuscular mycorrhiza in improving P efficiency of rice.
• The root colonization by arbuscular mycorrhizal fungi was enhanced by inoculation.
• Inoculation increased agronomic efficiency by decreasing P loss from paddy fields.
• The improved agrophysiological efficiency was not due to the altered P allocation.

Arbuscular mycorrhizal fungi (AMF) were supposed to improve phosphorus (P) efficiency in paddy fields. Our aim was to investigate the roles of AMF inoculation in increasing P acquisition efficiency (PAE) by cutting down P loss and in enhancing P use efficiency (PUE) via optimizing shoot P investment. A field experiment with two factors was carried out in northeast of China: six fertilizer levels were provided, inoculation with Glomus mosseae was either conducted or not at each fertilizer level. We investigated P loss during the rice growing season while P uptake and investment, biological and economic yields of rice were estimated at maturity. Then, we calculated recovery efficiency (RE), utilization efficiency (UE) and agronomic efficiency (AE) for PAE and physiological efficiency (PE) and agrophysiological efficiency (APE) for PUE. Both apparent and balanced values of these indicators were calculated. In addition, relationships of balanced PAE—P loss and balanced PUE—P investment were investigated for the two sets of plants. We found that AMF inoculation improved root colonization and the economic yield but decreased the biological yield and seasonal P loss. Inoculation led to more P allocated to panicles but less to stems and leaves, without affecting shoot P uptake. We also found that the apparent RE, UE and AE were smaller in inoculated treatments while greater apparent PE and balanced AE and APE was observed in inoculated treatments. Additionally, P loss of paddy fields decreased exponentially as balanced PAE increased and inoculation reduced P loss, without affecting balanced PAE. For the two sets of plants, balanced PE was negatively correlated with shoot P invested in panicles but positively with shoot P invested in stems. Furthermore, inoculation did not significantly altered the relationship between balanced PE and shoot P invested in panicles and stems. Conclusively, our study highlights the importance of AMF inoculation in improving P efficiency of rice production.