A disturbance in the aggregates: wildfire reorganizes microbial substrate use across contrasting climatic windows in volcanic soils of native and managed forests
摘要
Wildfires alter aggregate microhabitats that regulate microbial access to carbon in volcanic ash soils, but aggregate-scale catabolic responses across contrasting climatic windows remain poorly understood. The hypothesis was that wildfire would reduce cumulative substrate-induced respiration, with declines concentrated in native forest microaggregates and plantation macroaggregates. The MicroResp whole-soil multiple substrate-induced respiration (MSIR) assay quantified cumulative CO2-C production in topsoil (0–5 cm) macroaggregates (2000 –250 μm) and microaggregates (250 –53 μm) from paired burned and unburned Nothofagus forest and Pinus radiata plantation sites in La Araucanía, south-central Chile. The same five georeferenced points per condition were sampled in February 2024 (dry/warm) and August 2024 (wet/cool). Composite dry/warm samples provided chemical, wavelength-dispersive X-ray fluorescence (WDXRF), and X-ray micro-computed tomography (micro-CT) data for analysis. Across campaigns, amino-acid cumulative CO2-C in native-forest microaggregates decreased from 475 to 181 mg kg− 1 in the dry/warm campaign and from 535 to 342 mg kg− 1 in the wet/cool campaign, whereas carbohydrate responses in plantation macroaggregates decreased from 372 to 119 mg kg− 1 and from 419 to 234 mg kg− 1, respectively. Substrate-level log-response ratios and a normalized differential aggregate fire sensitivity (DAFS) index indicated that fire-associated declines were concentrated in native forest microaggregates and plantation macroaggregates. The results indicate that wildfires reorganized microbial substrate use within aggregates in ways that depended on ecosystem/site context and aggregate fraction, while structural and chemical descriptors should be interpreted as contextual information.