Signature Wood Modifications Reveal Decomposer Community History

Abstract

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.

Initial white rot type dominance of wood decomposition and its functional consequences in a regenerating tropical dry forest

“…These residue changes are a collective history of decomposer dominance (Worrall et al, 1997) among the diverse lineages, genomes, and lignocellulolytic strategies of wood-degrading fungi (Riley et al, 2014). In our work (Schilling et al, 2015) and similar to Worrall et al (1997), we found a 40% DAS threshold in decayed wood to adequately separate brown (>40%) from both white rot and sound wood (both <40%). This threshold is a weight-based percentage, and brown rot DAS in our study and the Worrall et al (1997) study tend to be much higher, often approaching 60e70%.…”

“…This threshold is a weight-based percentage, and brown rot DAS in our study and the Worrall et al (1997) study tend to be much higher, often approaching 60e70%. We also know that while there is a 'history effect' caveat for brown rot (once DAS is high, it stays high), if DAS is low coincident with density loss, it is safe to assume white rot, particularly if coupled with significant lignin loss (Schilling et al, 2015). In this study, dilute alkali solubility (wt%) of wood powders was measured in 0.2 M NaOH following protocols in Shortle et al (2010).…”

“…Dominant decomposer rot type and nutritional mode (i.e. carbohydrate versus lignin selectivity) were assessed indirectly by measuring residue dilute alkali solubility (DAS) and lignin loss, outlined in Schilling et al (2015). The two general fungal decay types (brown and white rot) have distinct influences on the solubility of wood residues in dilute alkali and residue lignin contents, both of which are distinctly higher for wood decomposing with brown rot than with white rot.…”

FUNGuild: An open annotation tool for parsing fungal community datasets by ecological guild

“…For example, additional trait metadata within guilds can also be directly incorporated into FUNGuild. To demonstrate this, we have assigned rot type (white vs. brown, but see Riley et al, 2014) to some taxa within wood decomposer guild to facilitate additional ecological inference in that group (Worrall et al, 1997;Schilling et al, 2015). A similar example involves ectomycorrhizal fungi, which have been increasingly classified according to their extraradical mycelial exploration types (Agerer, 2001;Tedersoo and Smith, 2013).…”

Localizing gene regulation reveals a staggered wood decay mechanism for the brown rot fungus Postia placenta

“…Accordingly, their decay mechanisms may provide a model for new biomass conversion technologies that not only function despite the presence of lignin but also yield lignin as a potentially useful coproduct (1)(2)(3). Deviating from their white rot ancestors, brown rot fungi have evolved mechanisms that are generally faster (4,5) and more polysaccharide-specific because they circumvent lignin (4,(6)(7)(8). This enhanced efficiency is coupled with losses, not expansions, of key white rot genes, including many linked to lignin degradation and processive cellulose hydrolysis.…”