Short-Term Kinetics of Soil Microbial Respiration — A General Parameter Across Scales?

Abstract

Microbial parameters derived from the short-term Michaelis-Menten type model are tested and applied on the ecosystem study. Soil dried immediately after sampling and stored at 4 o C was moistened to 60% water holding capacity and CO 2 production was measured (GC) after 24 h (respiration response to water supply, V DS ) and between the 5 th and 6 th day of incubation (basal respiration V BR ). Then glucose was added into the soil and CO 2 production was measured 16 to 24 h later (maximum respiration, V MAX ). Substrate saturation kinetics of respiration was measured after addition of glucose in 6 different concentrations. Soil heterotrophic respiratory potential was expressed as V DS /V MAX ratio; biologically available C (AC BR ) and potential flush of the biologically available C (AC DS /AC BR ) was estimated using Michaelis-Menten type model. It is shown that the above parameters can get relevant results because they meet the basic assumptions: (i) Fitting of Michaelis-Menten type model is accurate (R 2 R R = 0.956-0.994), (ii) microbial respiration is substrate limited in natural conditions, (iii) V MAX is relatively invariable for a wide range of C substrate concentrations and microbial populations are not growing. (iv) After moistening of the soil, extra C is released, the amount of which is characteristic for the given soil. Application of the short-term kinetic approach on the upper soil layer of various 229

Soil Heterotrophic Respiration Potential and Maximum Respiration Rate of Differently Managed Meadows

“…Carbon in the coarse fraction of the soil is weakly bound when related to that in the fine fraction, giving thus a high proportion of the available carbon (SANTRUCKOVA et al 2005). In our case, the proportions of different particle-size fractions were very similar on both meadows, and thus the texture was not the factor influencing the results obtained.…”

“…Its values in the range from 0.21 to 0.65 indicate, according to SANTRUCKOVA et al (2005), either a low quality of biologically available C or a low microbial biomass. The abandonment of the meadow caused an increase of V DS /V MAX and V MAX .…”

“…The abandonment of the meadow decelerated the nutrient cycling, and as reported in the work by FORMANEK et al (submitted for publication), Ah horizon of the abandoned meadow showed a higher net N immobilisation, probably as the result of a higher C availability and needs of N for its utilisation. The increasing temperature increases the solubility of organic compounds as well as the ability of microbial populations to produce extracellular enzymes and mineralise more complex organic materials (CHRIST & DAVID 1996;ANDREWS et al 2000;SANTRUCKOVA et al 2005). We do not have the information on the temperature differences in Ah horizon between both meadows studied, nevertheless, we suppose they are very small and insignificant.…”

“…CO 2 evolution was measured 24 h after moistening (respiration response to water supply, V DS ), between 5 th and 6 th days of incubation (basal respiration rate at 60% soil water content v/w, V BR ), and then after glucose amendment (3.64 mg C/g dry soil) between 6 th and 7 th days (maximum respiration rate, V MAX ) (SANTRUCKOVA et al 2005). Glucose was added to the soils as dry powder and mixed in thoroughly.…”

“…As stated in the work by SANTRUCKOVA et al (2005), soil heterotrophic respiratory potential is a function of microbial population size and physiology, C quality and availability. V MAX is controlled mainly by the size of microbial populations, growth physiology, and C quality (ANDERSON & DOMSCH 1978;PANIKOV 1995).…”