Microbial Community Shifts Reflect Losses of Native Soil Carbon with Pyrogenic and Fresh Organic Matter Additions and Are Greatest in Low-Carbon Soils

Abstract

Soil organic carbon (SOC) plays an important role in regulating global climate change, carbon and nutrient cycling in soils, and soil moisture. Organic matter (OM) additions to soils can affect the rate at which SOC is mineralized by microbes, with potentially important effects on SOC stocks. Understanding how pyrogenic organic matter (PyOM) affects the cycling of native SOC (nSOC) and the soil microbes responsible for these effects is important for fire-affected ecosystems as well as for biochar-amended systems. We used an incubation trial with five different soils from National Ecological Observatory Network sites across the US and 13C-labelled 350°C corn stover PyOM and fresh corn stover OM to trace nSOC-derived CO2 emissions with and without PyOM and OM amendments. We used high-throughput sequencing of rRNA genes to characterize bacterial, archaeal, and fungal communities and their response to PyOM and OM in soils that were previously stored at -80°C. We found that the effects of amendments on nSOC-derived CO2 reflected the unamended soil C status, where relative increases in C mineralization were greatest in low-C soils. OM additions produced much greater effects on nSOC-CO2 emissions than PyOM additions. Furthermore, the magnitude of microbial community composition change mirrored the magnitude of increases in nSOC-CO2, indicating a specific subset of microbes were likely responsible for the observed changes in nSOC mineralization. However, PyOM responders differed across soils and did not necessarily reflect a common “charosphere”. Overall, this study suggests that soils that already have low SOC may be particularly vulnerable to short-term increases in SOC loss with OM or PyOM additions. Importance Soil organic matter (SOM) has an important role in global climate change, carbon and nutrient cycling in soils, and soil moisture dynamics. Understanding the processes that affect SOM stocks is important for managing these functions. Recently, understanding how fire-affected organic matter (or “pyrogenic” organic matter (PyOM)) affects existing SOM stocks has become increasingly important, both due to changing fire regimes, and to interest in “biochar” – pyrogenic organic matter that is produced intentionally for carbon management or as an agricultural soil amendment. We found that soils with less SOM were more prone to increased losses with PyOM (and fresh organic matter) additions, and that soil microbial communities changed more in soils that also had greater SOM losses with PyOM additions. This suggests that soils that already have low SOM content may be particularly vulnerable to short-term increases in SOM loss, and that a subset of the soil microbial community is likely responsible for these effects.

13C Labelling of Litter Added to Tea (Camellia sinensis L.) Plantation Soil Reveals a Significant Positive Priming Effect That Leads to Less Soil Organic Carbon Accumulation

“…A structural equation model revealed that microbial communities associated with native SOC mineralization directly affected SOC (indicated as ∆C SOC+litter ), whereas microbial communities associated with litter degradation indirectly affected ∆C SOC+litter by changing β-glucosidase activity under litter incorporation (Figure 8). A previous study found that the magnitude of the microbial community composition mirrored the magnitude of increases in CO 2 derived from native SOC, indicating that a specific subset of microbes was likely responsible for the observed changes in native SOC mineralization [47].…”

Indigenously produced biochar retains fertility in sandy soil through unique microbial diversity sustenance: a step toward the circular economy

“…However, the total carbon decreased slightly. It has been demonstrated by other authors that the change in the microbial community with the addition of pyrogenic organic matter results in carbon loss from the soil, especially in low-carbon soil (Whitman et al, 2021 ). The nutritive and structural properties of biochar play an important role in changing the microbial community structure and activity in the soil (Zhang et al, 2018 ).…”

“…It is argued that the addition of organic matter to soil may not always translate into an increase in microbial diversity or number as different microbial communities respond differently to added organic matter. This may be due to the difference in the carbon use efficiency, carbon assimilation rates, and the ratio of various microbes in the soil (Whitman et al, 2021 ). Furthermore, the type of biochar also influences the microbial community structure.…”

Decreasing Soil Organic Carbon in Maize Cultivated Soil in Lowland Northern Thailand: Evidenced by the Interactions between Nutrients and Dissolved Organic Carbon

“…The SOC content can be influenced by labile carbon inputs, which can change the PE in soils [18]. The addition of labile carbon to low-SOC soils leads to greater increases in PE, especially in low-SOC soils, but also in soils already depleted by increased C input [18] For example, subsoil organic carbon mineralisation is more sensitive to labile carbon and N addition [117], and microbial activity plays a key role in promoting mineralisation [118]. This might be due to the increased SOC loss which occurred in the maize soil in this study.…”