Fire effects on ecosystems range from destruction of aboveground vegetation to direct and indirect effects on belowground microorganisms. Although variation in such effects is expected to be related to fire severity, another potentially important and poorly understood factor is the effect of fire seasonality on soil microorganisms. We carried out a large-scale field experiment examining the effects of spring (early-dry season) versus autumn (late-dry- season) burns on the community composition of soil fungi in a typical Mediterranean woodland. Although the intensity and severity of our prescribed burns were largely consistent between the two burning seasons, we detected differential fire season effects on the composition of the soil fungal community, driven by changes in the saprotrophic fungal guild. The community composition of ectomycorrhizal fungi, assayed both in pine seedling bioassays and from soil sequencing, appeared to be resilient to the variation inflicted by seasonal fires. Since changes in the soil saprotrophic fungal community can directly influence carbon emission and decomposition rates, we suggest that regardless of their intensity and severity, seasonal fires may cause changes in ecosystem functioning.

火灾对生态系统的影响范围从地上植被的破坏到对地下微生物的直接和间接影响。尽管预计这种影响的变化与火灾的严重程度有关，但另一个潜在的重要且人们尚未了解的因素是火灾季节对土壤微生物的影响。我们进行了一项大规模的田间试验，研究了春季（早干季）与秋季（晚干季）烧伤对典型地中海林地土壤真菌群落组成的影响。尽管我们规定的烧伤强度和严重程度在两个烧伤季节之间基本一致，但我们发现，由于腐生营养真菌协会的变化，烧伤季节对土壤真菌群落组成的影响不同。在松树幼苗生物测定法和土壤测序中测定的外生菌根真菌的群落组成似乎可以抵抗季节性火灾造成的变化。由于土壤营养缺陷型真菌群落的变化会直接影响碳的排放和分解速率，因此我们建议，不管季节的强度和严重程度，季节性火灾都可能导致生态系统功能的变化。