Microbially Derived Inputs to Soil Organic Matter: Are Current Estimates Too Low?

Abstract

Soil microbes are central to many soil processes, but due to the structural complexity of soil organic matter, the accurate quantification of microbial biomass contributions continues to pose a significant analytical challenge. In this study, microbes from a range of soils were cultured such that their molecular profile could be compared to that of soil organic matter and native vegetation. With the use of modern NMR spectroscopy, the contributions from microbial species can be discerned in soil organic matter and quantified. On the basis of these studies, the contributions of microbial biomass to soil organic matter appear to be much higher than the 1-5% reported by other researchers. In some soils, microbial biomass was found to contribute >50% of the extractable soil organic matter fractions and approximately 45% of the humin fraction and accounted for >80% of the soil nitrogen. These findings are significant because organic matter is intimately linked to nutrient release and transport in soils, nitrogen turnover rates, contaminant fate, soil quality, and fertility. Therefore, if in some cases soil organic matter and soil organic nitrogen are predominately of microbial origin, it is likely that this fraction, whether in the form of preserved material or living cells, plays an underestimated role in several soil processes.

Plant diversity increases soil microbial activity and soil carbon storage

“…The importance of microbial residues for soil carbon storage is suggested to even increase over time 23 . Thus, in line with the recent debate [42][43][44] , our findings challenge previous views underestimating or even negating the influence of size and activity of soil microorganisms on soil carbon storage.…”

Microbial community structure mediates response of soil C decomposition to litter addition and warming

“…SOM models that include microbial community structure have shown that changes in microbial physiology, often expressed as CUE (defined as the amount of C in microbial biomass relative to C respired and in biomass), have the potential to dramatically impact the fate of C stocks to climate change (Allison et al, 2010;Schimel, 2013;Wieder et al, 2013;Li et al, 2014), and experimental evidence shows that CUE can be altered by substrate quality, temperature, and N availability (Dijkstra et al, 2011;Manzoni et al, 2012;Frey et al, 2013;Tucker et al, 2013). This concept of changes to CUE is of particular importance as a large portion of SOM has been attributed to microbial derived products, which may have a relatively long turnover time (Simpson et al, 2007;Liang and Balser, 2008;Miltner et al, 2012;Gleixner, 2013). It is therefore necessary to determine the underlying mechanisms and the extent that microbial community structure and function impacts C turnover in response to these global change scenarios.…”

Refractory dissolved organic nitrogen accumulation in high-elevation lakes

“…The 1 H-13 C heteronuclear Single Quantum Coherence (HSQC) spectrum (Fig. 4a) clearly identifies the majority of peaks to be consistent with protein 26,27 . This is particularly evident for the protein a-C-H region (3.4-4.5 p.p.m.)…”