Plant growth is depending on the availability of nutrient in the soil. Free living organisms (such as bacteria, bacteria grazing protozoa and nematodes) and root symbionts (such as mykorrhiza, nitrogen fixating bacteria) help the plants by releasing nutrients for plant uptake (free-living organisms) or by taking up the nutrients for the plant (root symbionts). The microbial activity of root symbionts is fuelled from carbon within the plant whereas rhizodeposition of organic carbon in the soil feds the free-living organisms. We know already that the dominating plants on Brandbjerg have different organism associated with their roots.

The aim is to work with the function and structure of the rhizosphere community of different plants at different climatic conditions. The work will encompass soil sampling in climate manipulated field plots adjacent to the Climaite plots or sampling under well-defined conditions in plant growth chambers. Afterwards the population of bacteria, protozoa and nematodes can be quantified under the microscope and the amount of microbial activity can be measured by gas chromatography.

1) Drought, plant performance and the rhizosphere community. At field plots adjacent to the Climaite plots precipitation will be removed by covering different plant species with a roof. We will study how plant growth and the rhizosphere community respond to drying conditions. Plants, microbes and bacteriovores are all affected by drought. Whether the effects seen are direct or indirect via interactions with the other organisms is a question we will try to answer. 

2) Increased temperature, plant performance and the rhizosphere community. In growth chambers the dominating plants, Descampsia and Calluna will be grown at different temperatures. We will compare the respiration rate in soil with or without plant cover, and further more if the plant species influence the temperature response. In soil under Deshampsia which has a relatively higher exudation rate compared to Calluna, the soil activity could increase more as a response of the raised temperature than in soil under Calluna.

3) Soil nutrient availability, plant performance and the rhizosphere community. We assume that the rhizosphere community helps the plant to take up nutrients. It is a question if the plant will exude less if the nutrients are readily available. Under these conditions the plant might not have to feed its rhizosphere organisms to get inorganic N and P from microbial mineralization of organic matter, so the number of microorganism and bacterivores in the rhizosphere could decrease. We will study how nutrient additions to soil affect the rhizosphere community also with different plant species with has different dependencies on their rhizosphere organisms.

Contact (More contact info - press here):

Søren Christensen, KU, Schristensen@bi.ku.dk; Karen Stevnbak, KU, ksandersen@bi.ku.dk.