Leaf-ing an impression: Do disturbance-mediated genetic variations in plant functional traits influence temporal variations in forest litter chemistry and litter microbiomes?

Leaf litter chemistry and microbial functional capacity strongly regulate litter decomposition, which is an important step in the carbon cycle and soil organic matter formation. Interactions between ecosystem disturbance legacy and genetic variation in leaf chemistry are not typically evaluated in litter decomposition studies or in forest microbiome research, despite increasing evidence that intraspecific diversity affects ecosystem function across scales. To explore these relationships, we conducted a 477-day litter decomposition study within 18 genetically diverse experimental trembling aspen (Populus tremuloides) plots in Wisconsin (14 genotypes/plot). In 2014, we reduced tree density in half of the plots by 75% to examine disturbance-mediated variation in plant functional traits across genotypes. Past work from these plots showed that disturbance significantly affected a variety of plant functional traits across genotypes, particularly crown foliar mass and foliar leaf chemistry (see Cope et al., 2021, DOI: 10.1111/nph.17166). Results from our decomposition study showed no differences in litter decomposition rates between disturbance legacies but rates varied considerably among the plots, suggesting that forest floor microbial functional capacity could be more influenced by plot-specific conditions rather than disturbance legacy. Across all plots, litter lignin, fiber, and cellulose concentration increased during the experiment (all p < 0.05, R2 ≈ 0.40) and showed no relationship to disturbance legacy, while litter carbon-to-nitrogen ratios decreased over time and showed strong time x disturbance interactions (p < 0.001, R2 = 0.81). We expect to observe greater 16S gene copy numbers (associated with fast-growing bacterial taxa) and microbial biomass at earlier stages of litter decomposition and to decrease over time. Increasing lignin concentration should select for more specialized taxa capable of decomposing chemically complex substrates over time, likely leading to decreased bacterial diversity but increased fungal diversity. Our study will provide important insight into how disturbance legacy and genetic variation might affect relationships between forest litter chemistry and litter microbiomes and over time, and how these relationships might influence carbon cycling.