Below-ground interactions between a seedling soybean and preestablished soybean plant with and without mycorrhizal fungi. 1. Plant biomass, root growth, and mycorrhizal colonization

Abstract

Nurse-seedling relationships mediated below-ground are not well-known. Seedlings of a non-nodulating isoline of soybean were planted alone or with a 19 day old pre-established nodulating soybean as partner, with the vesicular-arbuscular mycorrhizal (VAM) fungi Glomus mosseae or control inoculum, and with one of four levels of below-ground barrier in the middle of the pot (no barrier, a 20 μm screen, 1 μ screen, or a solid barrier). This study asked how a stressed soybean seedling interacts below-ground with an older non-stressed soybean with and without VAM fungi, in terms of plant biomass, root growth and VAM colonization. Plants were grown for 53 days in a greenhouse with the seedlings on the north side of each pot, shaded by above-ground barriers in the middle of each pot. Non-nodulating soybeans grew best when growing alone with no below-ground barrier in the pot, least with a nodulated pre-established soybean as partner and intermediate when the pot was split in half by a solid barrier. Screen barrier treatments produced intermediate biomass values between the values for no barrier and solid barrier treatments. Biomass results were consistent with a model of resource competition with the larger established nodulated soybean being the superior competitor. Percent VAM colonization was highest in the seedlings when the plants were grown together. In spite of this result, VAM fungi did not change the competitive relations between the two plants.