Recurrent wildfires do more than sculpt the trees of Mediterranean forests; they leave a measurable signature in the fungal communities living in the soil beneath them. A study published in the journal Fire Ecology on 22 September 2026 reports that in Aleppo pine (Pinus halepensis) forests of eastern Spain, soils from areas with historically frequent crown fires hosted fungal communities with lower phylogenetic diversity than soils from areas with low fire recurrence. The research, led by L. Pérez-Izquierdo together with colleagues including M. Zabal-Aguirre, S. C. González-Martínez, M. Buée, M. Verdú and A. Rincón, also found that the traits of the trees themselves, rather than local climate or soil chemistry, were the strongest predictors of these underground community patterns.

The team worked with natural populations of Aleppo pine, a species widespread across the Mediterranean basin and well known for its fire adaptations, including serotinous cones that retain seeds in a canopy seed bank, early sexual maturity, and lower branches that can carry ground flames into the crown. Five pine populations were selected in areas with historically frequent crown fires, which the authors call HiFi populations, and three populations in zones with low fire recurrence, the LoFi populations. Fire history records for the region show that more than 50 percent of the high-recurrence area burned at least once between 1978 and 2001, compared with roughly 15 percent of the low-recurrence area. All stands were mature, with trees more than 40 years old.

The sampling design centered on individual trees. Five trees separated by more than 10 meters were chosen within each population, for a total of 40 trees, 25 in high-recurrence zones and 15 in low-recurrence zones. In May 2013, the researchers collected four soil samples around each tree, one at each cardinal orientation about a meter from the trunk, digging 10 by 10 by 20 centimeter holes after removing the litter layer. The four samples per tree were pooled, kept cool, and processed within 72 hours. These trees had previously been characterized for productivity and fire-adaptation traits such as bark thickness and serotiny, the proportion of closed cones among fully ripe cones.

Trees in the high-fire zones were strikingly different in phenotype. They were 76 percent more serotinous and had 12 percent greater diameter at breast height than trees in low-recurrence populations. Local climate also differed, with hotter and wetter conditions and lower altitude at the high-recurrence sites. To capture the genetic side of the story, 35 of the trees were genotyped with a single nucleotide polymorphism assay enriched for candidate genes underlying adaptive traits in Mediterranean pines, including stress responses, serotiny, wood properties, phenology and growth. Tree genetic distances differed between high- and low-recurrence populations, although the authors note this result was borderline in significance, partly because genotyping samples from five trees were missing.

In the laboratory, the team sequenced the ITS1 marker region of fungal DNA using Illumina MiSeq technology. After quality filtering and merging, 2,672,346 sequences remained from an initial set of more than 4.3 million, and these clustered into 6,967 fungal operational taxonomic units at a 97 percent similarity threshold. After rarefaction to equal sequencing depth, high-recurrence soils averaged 824 OTUs and low-recurrence soils 711, a difference that was not statistically significant. Basidiomycetes dominated the communities at 44 percent of total sequences, followed by Ascomycetes at 38 percent. The researchers then built an approximate fungal phylogeny from 3,102 OTUs and calculated two phylogeny-weighted metrics: the Net Relatedness Index, where higher values indicate lower phylodiversity, and a fuzzy-weighting index called PCPS that summarizes phylogenetic structure across the whole tree.

The phylogenetic results were clear. Soil fungal communities in high-recurrence zones were less phylodiverse, showing higher Net Relatedness Index values, and their phylogenetic structure pointed to an overrepresentation and clustering of the phylum Basidiomycota. In other words, co-occurring fungal taxa in frequently burned soils were more closely related than expected by chance, a pattern consistent with environmental filtering that favors competitive lineages. The first principal component of the phylogenetic structure, which captures the deepest evolutionary divergences among lineages, explained 34.6 percent of the total variance in community composition. Correlations between phylogenetic trees built by two different methods reached 0.999, supporting the robustness of the analysis.

Community composition also shifted by functional guild. Among the ten most abundant fungi in high-recurrence soils, five were ectomycorrhizal, and three were significantly indicative of that fire regime: Tricholoma batschii, 96 percent more abundant there than in low-recurrence soils, Suillus collinitus at 99.9 percent, and Amphinema sp. at 91 percent. In contrast, the ten most representative fungi in low-recurrence soils were saprophytic, with species such as Cryptococcus podzolicus, Penicillium restrictum, Archaeorhizomyces sp. and Umbelopsis sp. significantly more abundant. Across guilds, ectomycorrhizal fungi showed significantly higher relative abundance in high-recurrence populations, while molds prevailed in low-recurrence sites; yeasts and saprotrophs did not change with fire regime.

These phylogenetic and compositional patterns carried functional consequences. Potential soil enzymatic activities were measured on fresh soil using fluorogenic substrates for seven hydrolytic enzymes involved in carbon, nitrogen and phosphorus cycling. Activities of chitinase, which mobilizes nitrogen, and phosphatase, which mobilizes phosphorus, were 40 percent and 37 percent higher respectively in high-recurrence soils, while carbon-hydrolyzing enzymes such as glucosidase, cellobiohydrolase, xylosidase and glucuronidase did not differ between zones. Fungal phylogenetic indices and higher ectomycorrhizal abundance were significantly related to these elevated nitrogen- and phosphorus-mobilizing activities. The authors suggest that ectomycorrhizal fungi with medium- and long-distance soil exploration types, considered efficient in mobilizing water, phosphorus and nitrogen, may explain this link through extended soil colonization and enzymatic production.

Perhaps the most striking finding concerned what did and did not explain the fungal patterns. Both phylogenetic indices were significantly related to tree phenotypic traits, summarized through principal component axes of diameter, bark thickness and serotiny, and the structure index was also related to tree genotypes. Neither climate nor edaphic properties significantly explained the phylogenetic structure of soil fungal communities. The authors interpret this as evidence that the effects of frequent fires on fungi are largely indirect, mediated by fire-induced vegetation changes, with the plant host emerging as the key driver. They propose that Aleppo pine adaptation to recurrent fires may partly depend on association with soil symbiotic fungi, generating positive plant-fungal feedbacks in which fire-adapted hosts preferentially associate with fungi that enhance nutrient acquisition.

The study also documents the environmental backdrop that makes these feedbacks plausible. The mean fire-return interval in the study area fell dramatically from 397 years during 1873 to 1972 to 49 years during 1973 to 2006, and recent work in the Valencian Community indicates that short intervals of less than 10 years now occur alongside much longer ones. The authors frame recurrent fires as multiple events within the natural fire regime of Mediterranean ecosystems, where fire is a long-standing ecological and evolutionary driver. Because fungi are central players in plant-soil-microbial feedbacks, recovery of ecosystem structure and function after fire, and long-term ecosystem stability, may depend not only on plant communities but on their fungal partners as well.

The researchers are careful to acknowledge limitations. The taxonomic resolution of ITS1 amplicon sequencing restricted the phylogenetic reconstruction to the genus level, so evolutionary relationships and ecological differences among congeneric species could not be captured. The phylogeny was approximated from published taxonomic and phylogenetic information rather than inferred directly from sequence markers, introducing uncertainty from previously established relationships among fungal lineages. A sensitivity analysis based on repeated subsampling confirmed that the unbalanced design of five high-recurrence versus three low-recurrence populations did not distort the model inference. Even so, the authors argue that their approach successfully incorporates evolutionary information into fungal community analysis, and they suggest that these plant-fungal feedbacks could prove key for understanding Mediterranean fire ecology and for guiding future restoration programs after fire disturbances.

Subject of Research: Soil fungal community phylogenetic and functional responses to recurrent fire in Mediterranean Aleppo pine forests

Article Title: Tree traits drive phylogenetic and functional responses of soil fungal communities in Mediterranean forests subjected to recurrent fires

Article References: Pérez-Izquierdo, L., Zabal-Aguirre, M., González-Martínez, S. C., Buée, M., Verdú, M., & Rincón, A. (2026). Tree traits drive phylogenetic and functional responses of soil fungal communities in Mediterranean forests subjected to recurrent fires. Fire Ecology, 22(1), Article 145. https://doi.org/10.1186/s42408-026-00577-2

Image Credits: AI Generated

DOI: 10.1186/s42408-026-00577-2

Keywords: soil fungi, Aleppo pine, Mediterranean forests, fire recurrence, phylogenetic diversity, ectomycorrhizal fungi, Basidiomycota, soil enzymes, serotiny, nutrient cycling, Fire Ecology, Spain