The Relationship between Microbial Carbon and the Resource Quality of Soil Carbon

Abstract

The biological health of soil is an important aspect of soil quality because of the many critical functions performed by organisms in soil. Various indicators of soil quality have been proposed, but measurements of microbial biomass are most commonly used. During decomposition of plant residues in soil the relative intensities of the O-alkyl-C signal decreases and the alkyl-C signal increases in nuclear magnetic resonance (NMR) spectra. This leads to the suggestion that the alkyl-C to O-alkyl-C ratio of a soil may indicate the degree of decomposition. Consequently, the overall resource quality of soil C as a substrate for heterotrophic microorganisms may be inversely related to the alkyl-C to O-alkyl-C ratio. Our hypothesis is that a relationship exists between the size of the soil microbial community (microbial biomass) and the quality of soil carbon as a resource for microorganisms. New data have been combined with previously published data to show that there was a significant, negative correlation between the biomass C to total C (Cmic, to Corg) ratio and the alkyl-C to O-alkyl-C ratio (p < 0.01), which supports our hypothesis.

Influence of Stability and Origin of Organic Amendments on Humification in Semiarid Soils

“…This index has been proposed as an indicator of the capacity for decomposition of OM (Baldock et al, 1997;de Nobili et al, 2008) and also as a sensitive indicator of humification during the early stages of leaf material decomposition (Almendros et al, 2000). A high ratio indicates a highly decomposed OM, which consequently is more resistant to rapid C loss (Webster et al, 2001). In our study, soil HA and FA from both compostamended soils (CSS and CMW) showed higher alkyl C/0-alkyl C ratios than those of the SS-and MSW-amended soils after the 1-yr incubation, meaning that the humic fraction formed in compost-amended soils was more stable.…”

Studies on litter characterization using 13C NMR and assessment of microbial activity in natural forest and plantation crops’ (teak and rubber) soil ecosystems of Kerala, India

“…The presence of species such as lignin/tannin tend to slow down the decomposition process of litter considerably and are reported to be the most recalcitrant materials among the naturally occurring organic compounds (Hammel 1997). Webster et al (2001) and Hopkins et al (2000) reported that as ratio of alkyl-C to O-alkyl-C increases the resource quality as a substrate for heterotrophic microorganisms declines. The C species comprising polysaccharide C or carbohydrate C was invariably the largest group present in all the five litter species studied represented by the high peaks in the shift region 45-90 ppm (Fig.…”

“…Though many biological indicators of soil quality have been proposed (Elliot et al 1996;Pankhurst et al 1997), microbial biomass measurement through substrate induced respiration method is often preferred as it can be applied to a range of soils and due to easiness in its measurement (Webster et al 2001).…”

Carbon Sequestration in Soil

“…In contrast, a decrease was observed for the bound FA of both stubbed and woodland soil samples. The alkyl C to O -alkyl ratio has been suggested as an indicator of the decomposability of SOM (Baldock et al, 1997 ;Webster et al, 2001 ), high alkyl C to O -alkyl C ratios indicating a lower resource quality of SOM. All 13 C -NMR spectra of free FA display a strong signal in the O -alkyl C region and a lower proportion of N -alkyl and alkyl C than HA.…”