Soil moisture legacy effects: Impacts on soil nutrients, plants and mycorrhizal responsiveness

Although most land-plants form associations with arbuscular mycorrhizal fungi (AMF) as a means of optimising nutrient capture, legacy effects of altered soil moisture regimes on plant responses to arbuscular mycorrhizas (AM) have not been studied. As rainfall patters change with climate change, soil moisture legacy effects, and their impact on plants, soil and microbes may become increasingly important. Results of an experiment are presented in which soil was subjected to a range of different soil moisture regimes prior to planting a mycorrhiza-defective tomato mutant and its mycorrhizal wild-type progenitor. There were clear legacy effects of the soil moisture regime prior to planting on soil physicochemical properties, plant growth and nutrition, the formation of AM and mycorrhizal responsiveness. For example, in the Dry treatment the plants were well colonized by AM, there was a clear benefit to the plants in terms of mycorrhizal growth responses and mycorrhizal P responses. In contrast, in the Intermediate treatment AM colonisation was lower, there was little benefit in terms of mycorrhizal responses. Finally, in the Wet and Wet/Dry treatments AM colonization levels were similar (albeit lower) to those in the Dry treatment, but mycorrhizal growth responses were lower and more variable. Together, these results clearly indicate that soil nutrients, plant growth and nutrition and mycorrhizal responsiveness are affected by soil moisture legacy effect. Consequently, as we move into a period where more variable and intense rainfall amounts and patterns have been projected, we need to consider soil moisture legacy effects.