Initial Wood Substrate Composition, more so than Fungal or Oomycete Endophyte Communities, Explain Decay Trajectories Across Woody Species

Microbial organisms, environmental conditions, and their interactions govern ecosystem process rates. In wood decay, recent studies have illuminated the importance of priority effects, i.e. the identity of potential decomposers present early in community assembly, in determining decay rates. However, in diverse forests, available wood substrates can differ dramatically as habitats and resources for microbes, making it difficult to evaluate the relative importance of initial communities versus initial substrate and environmental conditions in setting the stage for decay. Given the importance of wood decomposition in the global carbon flux, improving our understanding of microbe-mediated decay in natural communities is vital.To address this, we characterized fungal and oomycete endophytes with amplicon sequencing from stems of 22 woody species growing in woodlands near Richmond, NSW, Australia and measured 11 traits to capture variation in the physical and chemical wood substrates. To evaluate the consequence of endophyte diversity and wood chemistry and ultrastructure on the trajectory of decay, stem samples were sequentially harvested over five years to quantify the rate, shape, and predictability of decay. We expected that particular initial endophyte compositions would lead to faster and more predictable decay; however, we did not find evidence to support this hypothesis. Initial wood attributes were much more helpful in explaining decay trajectories. For example, smaller, less dense stems with high water, low N, and low lignin concentrations led to faster and more predictable decay. These findings point to the importance of wood substrate-driven environmental filtering, rather than endophyte-driven priority effects, in directing the trajectory of decay across a diverse set of woody species.