Direct evidence for the role of microbial community composition in the formation of soil organic matter composition and persistence

Abstract

The largest terrestrial carbon sink on earth is soil carbon stocks. As the climate changes, the rate at which the Earth’s climate warms depends in part on the persistence of soil organic carbon. Microbial turnover forms the backbone of soil organic matter (SOM) formation and it has been recently proposed that SOM molecular complexity is a key driver of stability. Despite this, the links between microbial diversity, chemical complexity and biogeochemical nature of SOM remain missing. Here we tested the hypotheses that distinct microbial communities shape the composition of SOM, and microbial-derived SOM has distinct decomposition potential depending on its community of origin. We inoculated microbial communities of varying diversities into a model soil matrix amended with simple carbon (cellobiose) and measured the thermal stability of the resultant SOM. Using a Rock-Eval® ramped thermal analysis, we found that microbial community composition drives the chemical fingerprint of soil carbon. While diversity was not a driver of SOM composition, bacteria-only communities lead to more thermally labile soil C pools than communities with bacteria and fungi. Our results provide direct evidence for a link between microbial community structure, SOM composition, and thermal stability. This evidence demonstrates the relevance of soil microorganisms in building persistent SOM stocks.

Plant biodiversity promotes sustainable agriculture directly and via belowground effects

“…The decomposition of a greater diversity of C compounds could mean higher metabolic costs, resulting in more C remaining in soils [125]. New findings corroborate this theory: bacterial community composition explained the signature of newly formed SOM during microbial growth and more complex communities generated more persistent SOM in a model soil study that manipulated microbial diversity [121]. These findings provide insight that management of soils for maximum biological diversity may be a successful strategy to build persistent SOM stocks in agriculture.…”

“…Plant diversity is associated with increased microbial biomass [120] and respiration, and plant community functional composition is a strong predictor of mycorrhizal community composition [62]. Soil microbial communities in turn can promote ecosystem functions like decomposition [73,121] or mitigate greenhouse gas emissions from the soil [79,80]. The influence of soil microbial communities on ecosystem functioning might occur through interactions with the plant community or via alterations of soil properties like soil aggregation, which can impact, for example, water and oxygen percolation with consequences for plant growth.…”

“…The influence of soil microbial communities on ecosystem functioning might occur through interactions with the plant community or via alterations of soil properties like soil aggregation, which can impact, for example, water and oxygen percolation with consequences for plant growth. Soil microbial diversity positively affects soil aggregation [125], community growth efficiency [74], and the formation of soil organic matter [122] that is more persistent to decomposition [121]. In colors we highlight that we need to join insights that have been gained from research developments in soil microbial ecology, plant-soil feedback loops, and BEF research to design sustainable diversification schemes for agriculture.…”

“…For example, the Jena experiment set up in 2002 to evaluate the impact of plant diversity on ecosystem functions provided direct evidence that more diverse plant communities resulted in an increase in soil C stocks [14,120]. While plant exudates and root biomass are the primary source of C, ultimately it is the soil microorganisms that drive C sequestration [121]. Previously, the recalcitrance of less-reactive compounds and physical protection were thought to control soil C stocks.…”

“…Previously, the recalcitrance of less-reactive compounds and physical protection were thought to control soil C stocks. Recently, the importance of microbially derived SOM has been recognized [120][121][122][123]. When microbes metabolize C inputs (i.e., leaf litter, root exudates, organic amendments, or pre-existing C compounds), some C is allocated to growth, and the resulting biomass can contribute to soil organic carbon pools through exudation or cell death (see Figure 3 in main text).…”