Nutrient effects on microorganism communities in nutrient poor soils

Abstract: Better, more efficient fertilizers with great productivity and economic returns are needed, but it is important today to find fertilizers that are also sustainable. It is also important to carefully monitor their impact on the environment, including potential side-effects. In this context, the microbial communities that carry out numerous essential functions contributing to a functional ecosystem are of particular interest. The present study is a complement to a pot experiment that investigated the potential of different waste products for use as fertilizers and how they affect the microbial community. In the pot experiment, the clearest treatment change in microorganism community function was found in the fully fertilized treatment used as a positive control. The question was whether this was indirect, i.e. due to changes to plant growth, or due to a particular nutrient in the fully fertilized treatment. This complementary study sought to identify whether any of the individual nutrient(s) in the fully fertilized treatment affected the soil-microorganism community. This was done through two different incubation experiments (a main experiment and a secondary experiment) in which 12different nutrients were tested one by one on two soils with low concentrations of trace elements, potassium (K)and magnesium(Mg). Changes in microbial community composition in the soils were examined by measuring the Community Level Physiological Profiles (CLPP) using the MicroResp method. In the main experiment the incubation lasted for 13 weeks, with assays after 2 and 13 weeks. In the secondary experiment the incubation lasted for 2 weeks, with 4 assays. The results showed a change in physiological soil microbial profile after addition of nitrogen (N), K, Mg and the fully fertilized treatment. These four treatments also gave significantly higher soil electric conductivity than the other treatments, as did the fully fertilized treatment in the original pot experiment. Therefore, it is possible that electric conductivity is the factor causing the change in microbial community composition. However, there is also a possibility of a direct effect of K and Mg in the nutrient-poor soils studied.