Department of Plant and Microbial Biology, University of California, Berkeley, California, United States of America.
Department of Microbiology and Plant Pathology, University of California-Riverside, Riverside, California, United States of America.
PLoS One. 2020 Mar 4;15(3):e0222691. doi: 10.1371/journal.pone.0222691. eCollection 2020.
We have designed a pyrocosm to enable fine-scale dissection of post-fire soil microbial communities. Using it we show that the peak soil temperature achieved at a given depth occurs hours after the fire is out, lingers near this peak for a significant time, and is accurately predicted by soil depth and the mass of charcoal burned. Flash fuels that produce no large coals were found to have a negligible soil heating effect. Coupling this system with Illumina MiSeq sequencing of the control and post-fire soil we show that we can stimulate a rapid, massive response by Pyronema, a well-known genus of pyrophilous fungus, within two weeks of a test fire. This specific stimulation occurs in a background of many other fungal taxa that do not change noticeably with the fire, although there is an overall reduction in richness and evenness. We introduce a thermo-chemical gradient model to summarize the way that heat, soil depth and altered soil chemistry interact to create a predictable, depth-structured habitat for microbes in post-fire soils. Coupling this model with the temperature relationships found in the pyrocosms, we predict that the width of a survivable "goldilocks zone", which achieves temperatures that select for postfire-adapted microbes, will stay relatively constant across a range of fuel loads. In addition we predict that a larger necromass zone, containing labile carbon and nutrients from recently heat-killed organisms, will increase in size rapidly with addition of fuel and then remain nearly constant in size over a broad range of fuel loads. The simplicity of this experimental system, coupled with the availability of a set of sequenced, assembled and annotated genomes of pyrophilous fungi, offers a powerful tool for dissecting the ecology of post-fire microbial communities.
我们设计了一个热室，以实现对火灾后土壤微生物群落的精细剖析。利用它，我们发现，在给定深度下达到的峰值土壤温度出现在火灾熄灭数小时后，会在很长一段时间内保持在这个峰值附近，并且可以通过土壤深度和燃烧的木炭量准确预测。我们发现，不会产生大煤块的闪燃燃料对土壤加热的影响可以忽略不计。将这个系统与 Illumina MiSeq 对对照和火灾后土壤的测序相结合，我们表明，在试验火灾后的两周内，我们可以刺激 Pyronema（一种已知的嗜热真菌属）迅速、大规模地响应。这种特定的刺激发生在许多其他真菌类群的背景下，这些真菌类群与火灾没有明显变化，尽管整体丰富度和均匀度有所降低。我们引入了一个热化学梯度模型，以总结热量、土壤深度和改变的土壤化学相互作用的方式，为火灾后土壤中的微生物创造一个可预测的、深度结构的栖息地。将这个模型与热室中发现的温度关系相结合，我们预测，在一系列燃料负荷下，能够选择适应火灾后微生物的可生存“黄金地带”的宽度将保持相对稳定。此外，我们预测，一个更大的腐殖质区，包含最近热杀死的有机物中的易分解碳和养分，将随着燃料的增加而迅速增大，然后在广泛的燃料负荷范围内保持几乎恒定的大小。这个实验系统的简单性，加上一组已测序、组装和注释的嗜热真菌基因组，为剖析火灾后微生物群落的生态学提供了一个强大的工具。
