Is resource allocation and grain yield of rice altered by inoculation with arbuscular mycorrhizal fungi?

Aims Our study quantified the combined effects of fertilization and inoculation with arbuscular mycorrhizal fungi (AMF) on grain yield and allocation of biomass and nutrients in field-grown rice (Oryza sativa L.). Methods A two-factor experiment was conducted at a field site in northeast of China (in Shuangcheng, Heilongjiang Province, Songhua River basin): six nitrogen-phosphorus-potassium fertilizer levels were provided (0, 20, 40, 60, 80 and 100% of the local norm of fertilizer supply), with or without inoculation with Glomus mosseae. At maturity, we quantified the percentage of root length colonization by AMF, grain yield, shoot: root ratios, shoot N and P contents and nutrients allocated to panicles, leaves and stems. Important Findings As expected, inoculation resulted in greatly increased AMF colonization, which in turn led to higher shoot: root ratios and greater shoot N contents. Shoot: root ratios of inoculated rice increased with increasing fertilization while there was a significant interaction between fertilization and inoculation on shoot: root ratio. Additionally, AMF inoculation increased panicle: shoot ratios, panicle N: shoot N ratios and panicle P:shoot P ratios, especially in plants grown at low fertilizer levels. Importantly, inoculated rice exhibited higher grain yield, with the maximum improvement (near 62%) at the lower fertilizer end. Our results showed that (i) AMF-inoculated plants conform to the functional equilibrium theory, albeit to a reduced extent compared to non-inoculated plants and (ii) AMF inoculation resulted in greater allocation of shoot biomass to panicles and increased grain yield by stimulating N and P redistribution to panicles.