Arbuscular mycorrhizas increased tomato biomass and nutrition but did not affect local soil P availability or 16S bacterial community in the field

While interest in arbuscular mycorrhizal (AM) fungal effects on soil phosphorus (P) have recently increased, field experiments on this topic are lacking. While microcosm studies provided valuable insights, the lack of field studies represents a knowledge gap. Here, we present a field study in which we grew a mycorrhiza-defective tomato (Solanum lycopersicum L.) genotype (named rmc) and its mycorrhizal wild-type progenitor (named 76R) with and without additional fertiliser, using a drip-irrigation system to examine the impacts of the AM symbiosis on soil P availability and plant growth and nutrition. AM effects on fruit biomass and nutrients, soil nutrient availability, soil moisture and the soil bacterial community were examined. At the time of harvest, the AM tomato plants without fertiliser had the same early season fruit biomass and fruit nutrient concentrations as plants that received fertiliser. The presence of roots reduced the concentration of available soil P, ammonium and soil moisture in the top 10 cm soil layer. Arbuscular mycorrhizas did not significantly affect soil P availability, soil moisture, or 16S bacterial community composition. These findings suggest an indirect role for AM fungi in tomato production but not necessarily a direct role in determining soil physicochemical traits, during the one season that this experiment was conducted. While longer-term field studies may be required in the future, the present study provides new insights into impacts of AM fungi on P availability and uptake in a field soil system.