Interactive effects of nitrogen deposition and drought-stress on plant-soil feedbacks of Artemisia californica seedlings

Nitrogen (N) deposition and drought are major drivers of global change that will influence plant-soil feedbacks. We investigated how N availability, N-impacted soil communities and drought affect feedback in seedlings of a drought-deciduous mycorrhizal shrub, Artemisia californica. Seedlings were inoculated with soil from either a high or low deposition site or sterilized inoculum and grown with or without supplemental N and under well-watered or drought-stressed conditions. Inoculum, N and water had interactive effects on feedbacks. Seedlings grown in low deposition inoculum exhibited a neutral to positive feedback under drought and had the highest root to shoot ratios and mycorrhizal colonization. Seedlings inoculated with high N-deposition soil experienced a positive feedback when N fertilized and well-watered, but plants allocated large amounts of biomass to shoots and had a negative response to drought. The soil community mediates plant response to varying belowground resource availability. We found N-impacted communities may reduce mycorrhizal colonization and allocation to roots and provide less protection against drought. Our results highlight the context dependency of plant-soil feedbacks and the potential for climate change and N deposition to have interactive effects on these relationships.