Seedling treatments and phosphorus solution concentrations affect nodulation and nodule functions in soybean (Glycine max L.)

Abstract

The effect of three seedling treatments: T 0 , normal germination; T 1 , cotyledons removed; T 2 , cotyledons removed 5 days earlier than in T 1 ; and two phosphorus levels (P 0 and P 30 ) on nodulation and nodule function in soybean [Glycine max (L.) Merr.] were investigated in nutrient solution culture. The number of nodules formed at P 0 was in the order T 2 > T 0 > T 1 , but it was T 0 > T 2 > T 1 at P 30 . Nodule dry weight per plant had the same tendency as the nodule number. Nodule size (dry weight per nodule) in seedlings ranged from 0.601 to 1.089 mg in the order T 0 > T 1 > T 2 , regardless of P level. For example, nodule size in T 0 was larger by 86% and 52% than T 2 at P 0 and P 30 , respectively. Furthermore, regardless of P level, a specific acetylene reduction activity (ARA, µM C 2 H 4 /h/g nodule) increased with P content in seedlings, but no significant difference was found (P < 0.05). Leghemoglobin (Lb) content was not significantly affected by P level; however, seedlings (T 0 and T 1 ) significantly affected the Lb content per unit plant biomass (P < 0.05). All these results suggest that seedling P content plays a key role in nodulation and nodule function of soybean.