Microbial biomass in limed and perturbed areas in sandy grassland soils in Sweden

Abstract

This study was done in sandy grasslands in eastern Skane, Sweden, where three experiments were carried out to investigate the effect of changed soil conditions brought about by liming and soil perturbation on different microbial functional groups and how this change affects phosphorous in restoration of sand steppe vegetation in sandy grasslands. In the first experiment, liming was done in three strips of about 0.5 by 3m in June 2007 in order to elevate the soil pH in Rinkaby in a military training area. Sampling was carried out within and outside the strips (controls). In the second experiment, also in Rinkaby area, eight plots of 8 x 8m were delineated; perturbation by soil mixing was done in four of the plots and liming and soil mixing was carried out in the other four. In the third experiment in Lyngsjon area four replicates were carried out along a pH gradient and in each replicate 4 samples were collected. From each experiment, roots and soils samples were collected and amount of mycorrhizal fungi, saprophytic fungi and bacteria tissues were analyzed. Analysis was done using fatty acids and soil chemistry techniques. Biomass estimation was primarily done using the phospholipids fatty acids (PLFAs) technique. Soil chemistry analysis was done to determine the nutrients especially phosphorus (P) and the pH of the soil Although there were changes in the microbial community, there was no significant changes in limed and non-limed soils in Experiment 1, except for the arbuscular mycorrhizal roots ( t (11) = 2.283, p=0.035). In Experiment 2 there was also no significant changes in microbial biomass in the limed and perturbed plots and the perturbed plots alone, except in arbuscular mycorrhizal; AM roots (t (14) = 2.253, p= 0.014); bacteria (t (14) =1.090, p =0.346); Saprophytic fungi (t (14)= 0.708 p= 0.506). In Experiment 3 a regression line of [0.08, 2.43 x (value of pH and P respectively) - 0.485; r = 0.771] was observed showing correlation between arbuscular mycorrhizal in roots and pH and consequently phosphorous. For the saprophytic and bacteria the correlation was very weak, r = 0.344 and 0.396 respectively. There was higher microbial biomass of the functional groups in the limed and perturbed plots in comparison to perturbed plots only, having ratios of 14:1, 32:1 and 6:1 for bacteria, AM fungi and saprophytic fungi respectively. The arbuscular mycorrhizal fungal community changed upon pH shift in all of the three experiments. A weak tendency relationship between pH and P was observed in Experiment 2 and 3. Due to the weak tendencies relationship observed between pH and microbial biomass, the reason for the changes in the microbial community cannot be explained by pH alone, it's therefore important to know how pH affects other factors such as mineralization and solubilisation of nutrients, substrate quality and soil properties.