Impact of greenhouse practices on infective capacity of arbuscular mycorrhiza in peri-urban horticulture

The metropolitan area of Buenos Aires (Argentina) includes a peri-urban region where greenhouse horticulture is the main productive activity. Preventing soil degradation is a significant challenge for sustainable production in these conditions. In this study, the number of viable propagules of arbuscular mycorrhizal (AM) fungi and their initial infectivity was analyzed in soil derived from lettuce plants grown under different management practices (agroecological, organic, and conventional). The greenhouse soil of all productive systems was characterized by high pH values and elevated electrical conductivity. The principal management difference between agroecological versus conventional and organic farms was the presence of a greater diversity of non-cultivated plants. Agroecological management, with spontaneous plant growth on edges of cultivated plots, significantly enhanced AM spore counts, and infective propagule numbers. Nevertheless, effective mycorrhization of lettuce roots was low in all systems, suggesting a reduced AM inoculum infective potential under intensive greenhouse conditions. The spontaneous plant management gradient revealed that less disturbed greenhouse margins act as reservoirs, potentially making external inoculation unnecessary in agroecological systems. However, the greenhouse environment in all systems remained a barrier to effective establishment of symbiosis. This suggests that, even with a functional external inoculum, intensive greenhouse practices suppress successful crop colonization.