Soil pH and Soluble Organic Matter Shifts Exerted by Heating Affect Microbial Response

Abstract

Fire-induced alterations to soil pH and organic matter play an important role in the post-fire microbial response. However, the magnitude of which each parameter affects this response is still unclear. The main objective of this work was to determine the magnitude in which soil pH and organic matter fire-induced alterations condition the response of viable and cultivable micro-organisms using laboratory heating, mimicking a range of fire intensities. Four heating treatments were applied to unaltered forest soil: unheated, 300, 450, and 500 °C. In order to isolate the effect of nutrient or pH heating-induced changes, different culture media were prepared using soil:water extracts from the different heated soils, nutrient, and pH amendments. Each medium was inoculated with different dilutions of a microbial suspension from the same original, unaltered soil, and microbial abundance was estimated. Concurrently, freeze-dry aliquots from each soil:water extract were analyzed by pyrolysis-gas chromatography/mass spectrometry. The microbial abundance in media prepared with heated soil was lower than that in media prepared with unheated soil. Nutrient addition and pH compensation appear to promote microbial proliferation in unaltered and low-intensity heated treatments, but not in those heated at the highest temperatures. Soil organic matter characterization showed a reduction in the number of organic compounds in soil-heated treatments and a marked increase in aromatic compounds, which could be related to the observed low microbial proliferation.

Soil Organic Matter Molecular Composition Shifts Driven by Forest Regrowth or Pasture after Slash-and-Burn of Amazon Forest

“…Moreover, these plots highlight the strong contribution of pyrogenic compounds to the SOM of BAF, despite 20 months of forest regrowth since the slash-and-burn of the forest. High temperatures (>350 °C) close to the soil surface during fire in BAF [ 15 ] may have reduced soil microbial communities [ 24 ], and, coupled with the accumulation of compounds toxic to microorganisms such as PAHs in BAF after fire ( Table 2 ), likely hindered microbial proliferation and recovery in BAF. Consequently, a slow incorporation of new biomass added to soil into SOM composition can be expected [ 24 ].…”

“…High temperatures (>350 °C) close to the soil surface during fire in BAF [ 15 ] may have reduced soil microbial communities [ 24 ], and, coupled with the accumulation of compounds toxic to microorganisms such as PAHs in BAF after fire ( Table 2 ), likely hindered microbial proliferation and recovery in BAF. Consequently, a slow incorporation of new biomass added to soil into SOM composition can be expected [ 24 ]. The recalcitrant nature of PAHs and their toxicity to soil microorganisms add explanation to the 19% higher TOC content in BAF compared to NAF at 0–5 cm depth ( Table 1 ).…”

“…Usually, fire leads to a depletion of ligno-cellulosic and labile microbial-derived compounds and neoformation of C-condensed structures, conferring wider hydrophobicity and aromaticity indexes to SOM [ 19 , 20 , 21 , 22 , 23 ]. Together with a reduced soil microbial activity caused by fire [ 24 ], this partially explains the higher mean residence time of SOM observed in fire-affected soils compared to control sites [ 25 ].…”

Effects of fire and fire-induced changes in soil properties on post-burn soil respiration

“…Fire-driven increases in soil pH are attributed to ash deposition and thermal modification of OM (Giovannini and Lucchesi 1997, Bodí et al 2014, Araya et al 2017), with higher soil temperatures resulting in larger pH increases up to a point (Araya et al 2017, Bárcenas-Moreno et al 2022). Over time, erosion and leaching remove ash from the soil profile, resulting in soil pH returning to pre-burn levels (Bodí et al 2014, Matosziuk et al 2020).…”

Advancing horizons in vegetable cultivation: a journey from ageold practices to high-tech greenhouse cultivation—a review

“…The Best Management Practices strive to harmonize nutrient inputs and protect water sources while ensuring sustainable yields ( Liu et al., 2022a ). The pH spectrum intertwines with the soil microbial community impacting nutrient dynamics and bolstering plant health ( Husson, 2013 ; Bárcenas-Moreno et al., 2022 ). The oxidation–reduction potential (Eh) is a dimension that is yet to be extensively studied.…”