Solar radiation explains litter degradation along alpine elevation gradients better than other climatic or edaphic parameters

Abstract

Organic matter (OM) decomposition has been shown to vary across ecosystems, suggesting that variation in local ecological conditions influences this process. A better understanding of the ecological factors driving OM decomposition rates will allow to better predict the effect of ecosystem changes on the carbon cycle. While temperature and humidity have been put forward as the main drivers of OM decomposition, the concomitant role of other ecosystem properties, such as soil physicochemical properties, and local microbial communities, remains to be investigated within large-scale ecological gradients. To address this gap, we measured the decomposition of a standardized OM source – green tea and rooibos tea – across 24 sites spread within a full factorial design including elevation and exposition, and across two distinct bioclimatic regions in the Swiss Alps. By analyzing OM decomposition via 19 climatic, edaphic or soil microbial activity-related variables, which strongly varied across sites, we identified solar radiation as the primary source of variation of both green and rooibos teabags decomposition rate. This study thus highlights that while most variables, such as temperature or humidity, as well as soil microbial activity, do impact decomposition process, in combination with the measured pedo-climatic niche, solar radiation, very likely by means of indirect effects, best captures variation in OM degradation. For instance, high solar radiation might favor photodegradation, in turn speeding up the decomposition activity of the local microbial communities. Future work should thus disentangle the synergistic effects of the unique local microbial community and solar radiation on OM decomposition across different habitats.

Humus Forms and Organic Matter Decomposition in the Swiss Alps

“…Previous studies confirmed the suitability of this approach in terms of the representativeness of experimental comparisons of local litter with teabag decomposition dynamics [71,72]. As previously demonstrated by Didion et al [71], we confirmed the slowest decomposition rate at the alpine level and also that rooibos tea degraded slower than green tea [38]. In alpine environments, microtopography can play a decisive role in the spatial distribution of different humus systems and forms [73,74].…”

“…levels, and along two opposing facing slopes (north and south), for a total of 2 regions × 2 elevations × 2 slopes × 3 replicate plots = 24 sites. Moreover, we randomly chose three replicate plots separated by at least 100 m. Plot size varied according to the vegetation type [38]: in the conifer forests of the subalpine zone, the plots' area was 400 m 2 (20 m × 20 m), whereas in the grasslands of the alpine zone, they were 25 m 2 (5 m × 5 m). For plant taxonomy we used the Flore de la Suisse [39] and the Flora Helvetica [40].…”

“…Following the recommendation of [49], 10 green tea and 10 rooibos tea bags were buried pairwise at a depth of 5 cm in the A layers (Figure S1), in autumn just before the first snowfall in each plot. The burial locations were chosen to represent the general vegetation of the plot [38]. The next spring, after 8 to 9 months, the tea bags were carefully excavated, wiping off adherent soil particles, and dried at 40 • C for at least 48 h. The decomposition rate (k-percent of weight loss per day) for both tea types was next assessed using initial weight (wi), final weight (wf), and burial time as follows: [k = ((wi − wf)/ (wf × 100))/burial time].…”

Fine root decomposition in forest ecosystems: an ecological perspective

“…Given that temperature and precipitation are key influences of plant growth and decomposer activity, root decomposition is likely to be highly responsive to variations in these two parameters (Bonato et al, 2023;Semeraro et al, 2023). In addition, the availability of nutrients and C sources influences the response of microorganisms to climate change (Sullivan et al, 2019).…”