Weathering of pyrogenic organic matter induces fungal oxidative enzyme response in single culture inoculation experiments

Abstract

The addition of pyrogenic organic matter (PyOM), the aromatic carbon-rich product of the incomplete combustion of plant biomass or fossil fuels, to soil can influence the rate of microbial metabolism of native soil carbon. The interaction of soil heterotrophs with PyOM may be governed by the surficial chemical and physical properties of PyOM that evolve with environmental exposure. We present results of a 36-day laboratory incubation investigating the interaction of a common white-rot fungus, Trametes versicolor, with three forms of 13C-enriched (2.08 atom% 13C) PyOM derived from Pinus ponderosa (450 °C): one freshly produced, and two artificially weathered (254 nm, UV light-water treatment and water-leaching alone). Analysis (FTIR, XPS) of the UV-weathered PyOM showed increased aliphatic C–H content and oxidation of aromatic carbon relative to both the original and water-leached PyOM. The addition of both weathered forms of PyOM stimulated (positively primed) fungal respiration of the growth media, while the unaltered PyOM mildly inhibited (negatively primed) respiration. Artificial weathering resulted in higher oxidative (laccase and peroxidase) enzyme activity than unaltered PyOM, possibly the result of a diminished capacity to bind reactive substrates and extracellular enzymes after weathering. However, and contrary to expectations, simple water-leached weathering resulted in a relatively higher enzyme activity and respiration than that of UV-weathering. The 13C content of respired CO2 indicated negligible fungal oxidation of PyOM for all treatments, demonstrating the overall low microbial reactivity of this high temperature PyOM. The increased enzymatic and positive priming response of T. versicolor to weathered PyOM highlights the importance of weathering-induced chemistry in controlling PyOM–microbe–soil carbon interactions.

Interacting Controls of Pyrolysis Temperature and Plant Taxa on the Degradability of PyOM in Fire-Prone Northern Temperate Forest Soil

“…Our results suggest that the potential positive priming of insoluble fractions of PyOM by PyOM w is greater in higher-temperature PyOM treatments (T450 and T600), where the insoluble PyOM fraction is likely greater. This is in keeping with our previous study that showed that artificially aged PyOM, which was thought to have significant amounts of leachable C, induced the enhanced oxidative enzyme response from white-rot fungi in a single culture while not being degraded itself [22]. We attributed the lack of decomposition in Reference [22] to the absence of a soil microbial consortia (present here in this study), which may benefit from the oxidative enzyme response of fungi can could lead to the further solubilization of PyOM for direct metabolism by bacterial groups [17][18][19]23].…”

“…It is assumed that the first-order control on PyOM reactivity in soil is determined by the pyrolysis of the initial plant material, whereby PyOM becomes progressively condensed and aromatized with increasing pyrolysis temperature [5,13,14]. While PyOM may persist for long periods of time in soil due to its acquired physicochemistry and the promotion of stabilization through soil aggregation [15,16], it is susceptible to both abiotic and biotic decomposition processes, which are influenced by the soil microbial community composition [17][18][19], soil edaphic properties [8], and exposure to chemical and photo oxidants [20][21][22][23]. Direct microbial degradation has been extensively documented.…”

Changes in soil chemical properties as affected by pyrogenic organic matter amendment with different intensity and frequency

“…Pyrogenic organic matter (PyOM), also called biochar or black carbon derives from incomplete combustion of organic materials including plant biomass and fossil fuels (Gibson et al, 2016). Incorporation of PyOM into soil can alter soil physicochemical properties and carbon (C) from PyOM makes up~5-45% of soil organic C (SOC) (Glaser et al, 1998;Skjemstad et al, 2002).…”

“…Incorporation of PyOM into soil can alter soil physicochemical properties and carbon (C) from PyOM makes up~5-45% of soil organic C (SOC) (Glaser et al, 1998;Skjemstad et al, 2002). The PyOM is highly condensed aromatic substance with high hydrophobicity and low microbial accessibility (Gray et al, 2014;Gibson et al, 2016). After adding to soils, PyOM could be eventually oxidized through abiotic and biotic processes to be hydrophilic as incorporation of oxygen-containing functional groups and accessible to soil microorganisms (Gul et al, 2015;Zimmerman, 2010).…”

“…Field experiments usually apply PyOM into soils once (low frequency) (Major et al, 2010) or yearly for several times (high frequency) (Du et al, 2016), but few study compared the effect of these two different PyOM application ways on soil properties. Even being hydrophobic and highly aromatic at the initial stage of soil application, PyOM amendments could still supply labile components into soil which is hydrophilic and easily washed out by soil water (Gibson et al, 2016;Zimmerman, 2010). Higher frequency of PyOM amendment would continuously supply labile organic materials and complement the nutrients for plants through fresh PyOM amendment (Gibson et al, 2016).…”