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Effects of arbuscular mycorrhizal inoculation on growth, yield, nitrogen, and phosphorus nutrition of nodulating bean varieties in two soil substrates of contrasting fertility

Abstract:

A pot experiment was conducted to study the response of nodulated bean (Phaseolus vulgaris L.), vars. Ceca and Montalban, to inoculation with the arbuscular-mycorrhizae (AM) Glomus spurcum strain IES-3 and G. mosseae strain IES-8 in two non-sterilized non-amended soil substrates (S-1 and S-2) of contrasting fertility. S-1 was an acid soil (pH 5.0) with 77% exchangeable aluminum (A1), low available phosphorus (P) (3.5 μg g-1 dry soil) and 1.8% organic matter. S-2 was a soil with pH 7.0, 7.9 μg P g-1 dry soil, 9.6% organic matter and no exchangeable A1. Plants growing in S-1 (S-1 plants) and S-2 (S-2 plants) soils were sampled at the beginning of the flowering stage. S-1 and S-2 plants were nodulated by the rhizobial populations native of each soil. S-1 plants of both varieties did not respond to AM inoculation in term of shoot and root mass, P content, relative abundance of ureides (RAU) and seed yields. Only the total chlorophyll, chlorophyll-a, chlrophyll-a/b ratio and nodule mass were significantly enhanced in AM-inoculated plants. Increased total reducing sugars concentration was detected in roots of S-1 plants inoculated with G. mosseae. S-2 plants displayed significantly higher shoot and nodule mass as well as increased total chlorophyll, chlorophyll-a, chlorophyll-a/b ratio and P content than S- 1 plants, regardless of the variety and AM inoculation. S-2 plants of the var Ceca showed a two fold increase in seed yields but similar RAU values (>60%) when compared to S-1 plants of the same variety. In contrast, the significant increase in RAU detected in S-2 plants of the var Montalban was not translated into higher seed yields. In S-2, the productivity of plants of the var Ceca doubled that of the var Montalban. For both bean varieties the highest significant P content and seed yield were observed exclusively in S-2 plants inoculated with G. mosseae. This Glomelean strain enhanced the sink-source ratio of the S-2 plants as evidenced by the higher total reducing sugar concentration in the root mass. Arbuscular-mycorrhizae inoculation significantly decreased the acid phosphatase activity in the rhizosphere of S-1 and S-2 plants, respectively, pointing toward a negative effect of foreign AM on the native microbial biomass. The effectiveness of the rhizobial populations native of each soil type and the weak response elicited by G. mosseae in S-2 plants do not justify, at present, the inclusion of foreign inocula in the bean crops carried out at S-1 and S-2 soils of the Sucre State of Venezuela. Results also indicated the higher adaptability of var Ceca to conditions prevailing in S-1 and S-2.