Towards improved stratified random studies of tundra
decomposition
Although our findings were overall inconclusive with regard to
quantifying controls of tundra decomposition dynamics, they point to
potential avenues for improving Arctic decomposition studies.
Incubating locally sampled litter alongside standardised substrate, in
addition to including community traits as explanatory variables, would
be an essential step to contextualise decomposition patterns in standard
litter and enable more precise conclusions on feedbacks of vegetation
change on decomposition (Joly et al. 2023). In a laboratory experiment,
Duddigan et al. (2020) found that both tea types generally follow
patterns of natural leaf litter decomposition, and studies in specific
alpine (Didion et al. 2016, von Oppen 2017) and Arctic (Thomas et al.
2023) sites have shown that the two tea types well represent mass loss
in local litter. However, a comparative study is still missing for the
Arctic tundra biome at large, resulting in uncertainty about the
representativeness of mass loss rates inferred from standard substrate.
More generally though, the informative value of standard-litter
experiments can be limited if nutritional differences between local
litter and standard substrate are not accounted for explicitly (Joly et
al. 2023). Given the importance of tundra carbon cycling, a systematic
assessment of the representativeness of standard decomposition protocols
(e.g., TBI) will be essential for adequate quantification of litter
decomposition in Arctic environments.
Many regions across the Arctic tundra biome are experiencing notable
vegetation changes in response to warming or degrading permafrost
(Heijmans et al. 2022). However, a lack of coordinated systematic
investigations of tundra decomposition dynamics across tundra zones and
habitat types, is impeding biome-wide predictions of tundra carbon
dynamics (Bonan et al. 2013); but see Thomas et al. 2023). Large-scale
replication of stratified-random sampling could fill this gap, enabling
representative sampling of environmental gradients across and within
sites, as well as evaluation of the relative importance of macro- vs.
microclimate for tundra litter decomposition (Joly et al. 2023). Our
findings underline the importance of considering variables representing
the complete decomposition process, particularly decomposer organisms as
well as both local and standard litter, and both fine- and more
broad-scale environmental data. Ultimately, such coordinated studies
could be of high value to inform predictions of the future carbon
balance of tundra soils with projected vegetation and environmental
changes (van Gestel et al. 2018).
Conclusion
We incubated two types of standard litter of contrasting quality (Green
Tea and Rooibos Tea) over 14 months across an Arctic tundra landscape,
covering several environmental gradients of topography, vegetation, soil
and microclimate. Although we found significant links between
topography, vegetation, soils and microclimate, the micro-environmental
variation itself explained little variation in decomposition responses.
This suggests that other factors not accounted for in our study, like
long-term moisture availability, snow patterns, or other seasonal
effects might control activity and community composition of decomposers.
Nonetheless, our systematic approach could serve as guidance for
coordinated studies of tundra decomposition dynamics, particularly
across large extents. Further research should explicitly include local
litter material, decomposer communities, and temporal variation to
improve model fit and explanatory power, and to support better
predictions of Arctic tundra litter decomposition and carbon cycling
dynamics.