SOIL RESPIRATION AS MICROBIAL RESPONSE TO THE ENDOGEN INPUT OF BIO-SYNTHESIZED ORGANIC MATTER AND ITS IMPLICATION IN CARBON SEQUESTRATION

Abstract

Active C, as a measure of the level of chemical oxidation of organic matter, reflects the carbon available to microorganisms. Soil respiration, as a direct way to estimate edaphic microbial activity, could be a measure of the fluctuations of carbon stocks in soils. To determine the ability of soil respiration to evaluate such fluctuations we used soils with an increased content of organic carbon, constant optimal conditions, to eliminate the disturbing factors, analyzed in a short period of time. The influence of the specific decomposition rates of these soils was assessed by both spot determinations of soil respiration and analyzing the flux of CO2 from ex situ soil samples, under standard experimental conditions, to highlight carbon storage in such soils. Reference data can be accumulated through the analysis of these parameters, which compared with the results of quantitative/qualitative determinations regarding the changes in the content of microbial biomass, the content of fulvic sub-fractions, the fluorescence of dissolved organic material and the evolution of the content of siderophores, could be considered, by their own evolutions, as arguments in sustaining the use of respiration in the efficient estimation of carbon storage evolution in the soils. The analyses of these parameters were carried out in two phases, for comparing initial and final data of experiment (after 30 days). The soils had different levels of the respiration potential between phases. The level of soil respiration was reduced in time between 4.27-14.60%, in each soil. The CO2 flux showed, in time, a continuous decreasing trend in both soils. In the case of Mollic Histic Gleysol (Salinic), the coefficient of determination has the value R2=0.92 for the flux determined in the final phase. The levels of microbial biomass of both soils were increased significantly at the end of the experiment. In the case of Mollic Histic Gleysol (Salinic), microbial biomass increased from 456±23.12 μgC∙g-1 to 514±24.57 μgC∙g-1 soil. The fulvic sub-fractions A-D of both soils revealed significant accumulates of soluble organic compounds, with different molecular weights and complexity levels, after 30 days of incubations in standard conditions. The fluorescent components present in the water-extractable organic matter were highlighted by imagistic method. The highest degree of storages of newly bio-synthesized compounds of carbon was registered in organic matter of Mollic Histic Gleysol (Salinic). The intensity of siderophores biosynthesis increased over time, starting from an initial lower presence in the Mollic Gleysol (Salinic) (with Ø 11 mm halo), which were followed by an increasing of siderophores content and availability of iron, at the end of the experimental period. Accumulations of siderophores in the Mollic Histic Gleysol (Salinic) determined a Ø 31 mm halo diameter.