Summary Priority effects among wood decomposers have been demonstrated by manipulating fungal assembly history via inoculations in dead wood and then tracking community development using DNA sequencing. Individual wood‐degrading fungi have been shown, however, to initiate decay after having colonized living trees as endophytes. To track these ‘upstream’ colonizers across the endophyte–saprophyte transition, we coupled high‐throughput sequencing with wood physiochemical analyses in stem sections extracted from healthy birch trees (Betula papyrifera; 4–7 cm dia.). We incubated wood in microcosms, limiting communities as endophytes−only or challenging endophytes with Fomes fomentarius or Piptoporus betulinus at high exogenous inoculum potential. Initial fungal richness in birch stems averaged 143 OTUs and decreased nearly threefold after five months of decomposition. Although F. fomentarius successfully colonized some stem sections incubated at 25 °C, decayed wood was generally dominated by saprophytic fungi that were present originally in lower abundances as endophytes. Among saprophytes, fungi in the brown rot functional guild consistently dominated, matching wood residues bearing the chemical hallmarks of brown rot. Despite this functionally redundant outcome, the taxa that rose to dominate in individual sections varied. Surprisingly, the brown rot taxa dominating wood decomposition were better known for lumber degradation rather than log decay in ground contact. Given the isolation from colonizers in our design, this redundancy of brown rot as the outcome suggests that these taxa and more generally brown rot fungi could have adapted to decompose wood where there is lower competitive pressure. Competitive avoidance would complement the diffuse depolymerization mechanisms of brown rot fungi, which are likely more prone to sugar pilfering by other organisms than the processive depolymerization mechanisms of white rot fungi. Overall, this guild‐level predictability of fungal endophyte development and consequence is encouraging given the challenges of predicting wood decomposition, and it provides a base for testing these dynamics under increasing natural complexity.

Correlating plant litter decay rates with initial tissue traits (e.g. C, N contents) is common practice, but in woody litter, predictive relationships are often weak. Variability in predicting wood decomposition is partially due to territorial competition among fungal decomposers that, in turn, have a range of nutritional strategies (rot types) and consequences on residues. Given this biotic influence, researchers are increasingly using culture-independent tools in an attempt to link variability more directly to decomposer groups. Our goal was to complement these tools by using certain wood modifications as ‘signatures’ that provide more functional information about decomposer dominance than density loss. Specifically, we used dilute alkali solubility (DAS; higher for brown rot) and lignin:density loss (L:D; higher for white rot) to infer rot type (binary) and fungal nutritional mode (gradient), respectively. We first determined strength of pattern among 29 fungi of known rot type by correlating DAS and L:D with mass loss in birch and pine. Having shown robust relationships for both techniques above a density loss threshold, we then demonstrated and resolved two issues relevant to species consortia and field trials, 1) spatial patchiness creating gravimetric bias (density bias), and 2) brown rot imprints prior or subsequent to white rot replacement (legacy effects). Finally, we field-tested our methods in a New Zealand Pinus radiata plantation in a paired-plot comparison. Overall, results validate these low-cost techniques that measure the collective histories of decomposer dominance in wood. The L:D measure also showed clear potential in classifying ‘rot type’ along a spectrum rather than as a traditional binary type (brown versus white rot), as it places the nutritional strategies of wood-degrading fungi on a scale (L:D=0-5, in this case). These information-rich measures of consequence can provide insight into their biological causes, strengthening the links between traits, structure, and function during wood decomposition.

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B i o r e m e d i a t i o n a n d B i o d e g r a d a t i o n

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