Effect of Climate Warming on Alpine Soil Decomposition in Western Norway: The Tea Bag Index and soil respiration along an altitudinal gradient

Litter decomposition in soils is a microbial process linked to soil respiration, affected by soil composition as well as environmental factors such as temperature and moisture. For alpine areas in particular, these stand to vary significantly with climate change. To characterize the impacts of these projected changes on the carbon fluxes and carbon cycling in the environment, this study uses turf transplants along an altitudinal gradient in Western Norway. Warming is simulated for alpine and subalpine soils. Because the soils differ in composition, this enables the quantification of the influence of soil composition on soil litter decomposition and respiration. Decomposition is quantified using the standard Tea Bag Index (TBI) where the mass loss of buried rooibos and green tea bags over an extended period is used to model the labile and recalcitrant fraction of litter in the soil. Respiration CO2 fluxes are quantified from concentration measurements in an infrared gas analyzer (IRGA, LI-84A, LICOR) across a prescribed period and bare soil area. Results from this study show that simultaneous optimal soil moisture and temperature conditions maximize soil respiration and litter decomposition rates. These optimal ranges are 15-35% for soil moisture and the maximum measured 22 oC for temperature. However, the impacts of the conditions individually are more complex: soil moisture is positively correlated with soil respiration, while the correlation with temperature is inconclusive. Decomposition rates and stabilization factors for the Liahovden, the alpine site, consistently exceed those for Joasete, the sub-alpine site, which contains less soil organic matter (SOM) and carbon. With warming, Joasete exhibits opposing behavior to that of Liahovden: reduced decomposition rates and litter stabilization. These findings suggest that the availability of nutrients due to soil moisture and the soil composition itself are the most important factors determining the carbon emissions and cycling in the soil. Nevertheless, under coupled optimal conditions (warmer climate with soil moisture at approximately 35%), there is a clear maximum in flux. The complexity of the interrelations of soil moisture and temperature for different soil types supports further research on the topic, with more replicates and soil moisture content variation plot by plot