Growth, assimilate partitioning and grain yield response of soybean (Glycine max L. Merrrill) varieties to carbon dioxide enrichment and arbuscular mycorrhizal fungi in the humid rainforest

Abstract

This investigation tested variation in the growth components, assimilate partitioning and grain yield of soybean (Glycine max L. Merrrill) varieties established in CO₂ enriched atmosphere when inoculated with mixtures of Arbuscular mycorrhizal fungi (AMF) species in the humid rainforest of Nigeria. A pot and a field experiment were established in Abeokuta (7°15’N, 3°28’E; 75 m asl), Nigeria in 2015. The pot experiment had CO₂ concentration, AMF inoculation and soybean varieties as treatments, in completely randomised design, repeated three times. On the field the treatments were in a split split-plot arrangement fitted into randomised complete block design. The main plot had CO₂ concentration [ambient (≈385 ppm) and elevated (≈550 ppm)], AMF inoculation in the sub plot (+ AMF and – AMF), while the sub sub-plot were soybean varieties (TGx 1448-2E, TGx 1440-1E and TGx 1740-2F), replicated three times. In both experiments assimilatory surface increased in CO₂ enriched atmosphere, with increased relative growth rate. The increased relative growth rate on the field was with increased leaf relative growth rate, reduced leaf area ratio and increased net assimilatory rate. Both trials had higher grain yield at elevated CO₂ than the ambient. Growth response to AMF inoculation was with reduced specific leaf area and increased leaf weight ratio. Soybean variety TGx 1448 -2E was more adaptive to variation in AMF inoculation and CO₂ enrichment. Soybean TGx 1740-2F was more responsive to combined effect of AMF inoculation and CO₂ enrichment, but less suitable in the absence of both in this ecology.

Keywords: Assimilatory surface, carbon dioxide enrichment, inoculation, soybean