Abstract
High concentrations of soil Al3+ in acid soil severely influence the growth of Medicago sativa (alfalfa). The objective of the current study was to analyze whether Arbuscular Mycorrhizal Fungi (AMF) inoculation could improve alfalfa growth in acid soils. A two-way completely randomized factorial design was employed for M. sativa and M. lupulina (black medick) with two inoculations (rhizobia and AMF) and three Al3+ levels, and replicated four times. The soil Al3+ levels were adjusted to 900 mg/kg, 1000 mg/kg and 1100 mg/kg. Spores of AMF were isolated directly from rhizosphere soils of black medick. The rhizobia were isolated from root nodules in fields separately from two plant species. At each Al3+ level, there were four inoculations, non-inoculation, AMF solely, rhizobia solely and dual-inoculation with AMF and rhizobia. Soil Al3+ concentration significantly limited above- and below-ground growth of both alfalfa and black medick, reducing plant height, branching number, shoot and root weight, and root length, surface area and volume. Compared to rhizobia, AMF showed a higher tolerance to soil Al3+. AMF inoculation increased the shoot and root weight of both plant species under most circumstances. Overall, AMF colonization had a trend in increasing the contents of phosphorus in both plant species at all Al3+ concentrations but not nitrogen and potassium. Dual inoculation significantly increased nodulation ability, enabling both plant species to form nodules at 900 and 1000 mg/kg Al3+. Though the soil Al3+ concentration influenced the efficiency of AMF inoculation, AMF inoculation improved nodulation, increased plant growth and nutrient uptake, suggesting that it was an alternative way in improving alfalfa growth in acid soils.
Highlights
Medicago sativa L., a perennial legume crop, is widely grown in temperate and subtropical regions all over the world for its high feeding value, good palatability, great adaptability, and high yield
A long-term cover cropping with black medic showed that Triticum aestivum following black medic had a higher early percent root length colonized by Arbuscular Mycorrhizal Fungi (AMF), suggesting that cover cropping with black medic was an effective method of increasing early AMF colonization (Turmel, 2007). These results suggested that AMF from black medick might be effective in low fertility soils, benefiting its wide distribution
The two-way ANOVA analysis indicated that soil Al3+ levels significantly influenced all parameters from both plants and soils, whereas inoculations significantly influenced shoot weight, root/shoot ratio, phosphorus concentration in plant, root length, surface area and volume from both plant species, and all soil parameters except soil pH for M. lupulina (Table 2)
Summary
Medicago sativa L. (alfalfa), a perennial legume crop, is widely grown in temperate and subtropical regions all over the world for its high feeding value, good palatability, great adaptability, and high yield. Soil acidity has become one of the limiting factors in planting alfalfa in the South of China (Guo, Ni, Yuan, & Huang, 2009). With the reduced pH levels in acid soils, alfalfa yield declines rapidly (Undersander et al, 1991), so do the nodulation, leaf retention, leaf to stem ratio, and crude protein content (Grewal & Williams, 2003). Among the factors decreasing soil fertilities in acid soil, aluminum (Al) toxicity has been regarded as the main factor limiting crop yields (Foy, 1988). In soils with pH below 5.5, the solubility of aluminum increases greatly and is released into the soil solution in the form of toxic ions to plants [Al(OH)2+, Al(OH)2+, Al3+ and Al(H2O)63+] (Kochian, Piñeros, & Hoekenga, 2004; Rouphael, Cardarelli, & Colla, 2015). Increased concentrations of Al3+ caused damage to the root tip, leading to the inhibition of root growth, and jas.ccsenet.org
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