Habitat‐specific effects of bark on wood decomposition: Influences of fragmentation, nitrogen concentration and microbial community composition

Abstract

1. Identifying the drivers of decomposition is critical for understanding carbon cycling dynamics in forest ecosystems. Woody biomass is an important pool of carbon, composed of bark and underlying wood which vary in structure, nutrient concentrations and exposure to the environment. We hypothesized that higher nutrient concentrations in bark would speed the decomposition of underlying wood, and that this effect would be greater in streams, where nutrients are less available to decomposers than on land.2. Replicate branches of three tree species, with and without bark, were placed in streams and on land in a lowland tropical forest in Panama. After 3 and 11 months of decomposition, we measured mass loss and nitrogen (N) concentrations and sequenced the fungal and bacterial communities of both wood and bark tissues.3. While bark decomposed faster than the underlying wood and had higher N concentrations, bark presence slowed wood mass loss. Nitrogen concentration could account for interspecific variation in wood mass loss, but not bark mass loss. In contrast, bark mass loss, but not wood mass loss, was faster in streams than on land, suggesting fragmentation is more important for bark mass loss in streams.Differences in fungal and bacterial community composition between bark and wood substrates were significant but small. 4.Our results indicate that bark can slow wood decomposition instead of promoting it, and that at least for branch wood, the primary drivers of decomposition differ between bark and wood. Differences in the factors driving decomposition rate between bark and wood suggest that the contribution of bark to the decomposition of woody biomass may depend on habitat. K E Y W O R D Saquatic, bacterial communities, decay, freshwater streams, fungal communities, tropical forest | INTRODUC TI ONA key goal of ecosystem ecology was to understand how carbon and nutrients cycle through ecosystems, and in turn influence ecosystem stability, productivity and diversity. Wood decomposition, which includes biotic decay processes, leaching and fragmentation

Influences of the bark economics spectrum and positive termite feedback on bark and xylem decomposition

“…S6b). This result implies there is a strong potential afterlife effect of BES on xylem decomposition besides XES itself, which corroborates previous research on the importance of the effect of bark during deadwood decomposition (Zuo et al 2016, Dossa et al 2018, Jones et al 2020.…”

“…2020, Jones et al. 2020). However, highly distinctive plant organs in terms of chemical and structural properties have dissimilar decomposition patterns with different ecological implications (Dossa et al.…”

“…Ecologists believe, on the one hand, that bark still partially maintains its defensive ability (e.g., ample defensive compounds) after tree death and thereby retards xylem decomposition (Jones et al. 2020), on the other hand, nutrient‐rich bark tissue could facilitate xylem decay underlying it (Dossa et al. 2018).…”

“…Several recent studies have demonstrated how interspecific variation in deadwood decomposability at local to regional scale can be predicted to some degree from multivariate variation in stem traits (van Geffen et al 2010, Zanne et al 2015, Zuo et al 2018 or from individual underlying xylem traits, such as dry matter content, lignin content, pH, vessel diameter, or nutrient content (Cornwell et al 2009, Freschet et al 2012, Liu et al 2015, Hu et al 2018. However, a prominent shortcoming of these previous studies on traits and deadwood decomposition is that they considered deadwood as a single unit, without distinguishing between xylem (underlying wood) and bark (but see Dossa et al 2018, Chang et al 2020, Jones et al 2020). However, highly distinctive plant organs in terms of chemical and structural properties have dissimilar decomposition patterns with different ecological implications (Dossa et al 2018).…”

“…Depending on the species and study, the presence of bark imposes either inhibitory or stimulatory effects on wood decay rate (Ulyshen et al 2016, Dossa et al 2018. Ecologists believe, on the one hand, that bark still partially maintains its defensive ability (e.g., ample defensive compounds) after tree death and thereby retards xylem decomposition (Jones et al 2020), on the other hand, nutrient-rich bark tissue could facilitate xylem decay underlying it (Dossa et al 2018). The inconsistency with previous findings remains poorly understood.…”