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Abstract
BackgroundThe glaciers in the Alps, as in other high mountain ranges and boreal zones, are generally retreating and leaving a wide surface of bare ground free from ice cover. This early stage soil is then colonized by microbes and vegetation in a process of primary succession. It is rarely experimentally examined whether this colonization process is linear or not at the ecosystem scale. Thus, to improve our understanding of the variables involved in the carbon accumulation in the different stages of primary succession, we conducted this research in three transects on the Matsch glacier forefield (Alps, N Italy) at an altitude between 2,350 and 2,800 m a.s.l.MethodsIn three field campaigns (July, August and September 2014) a closed transparent chamber was used to quantify the net ecosystem exchange (NEE) between the natural vegetation and the atmosphere. On the five plots established in each of the three transects, shading nets were used to determine ecosystem response function to variable light conditions. Ecosystem respiration (Reco) and gross ecosystem exchange (GEE) was partitioned from NEE. Following the final flux measurements, biometric sampling was conducted to establish soil carbon (C) and nitrogen (N) content and the biomass components for each transect.ResultsA clear difference was found between the earlier and the later successional stage. The older successional stages in the lower altitudes acted as a stronger C sink, where NEE, GEE and Reco were significantly higher than in the earlier successional stage. Of the two lower transects, the sink capacity of intermediate-succession plots exceeded that of the plots of older formation, in spite of the more developed soil. Total biomass (above- and belowground) approached its maximum value in the intermediate ecosystem, whilst the later stage of succession predominated in the corresponding belowground organic mass (biomass, N and C).OutlookWe found that the process of carbon accumulation along a glacier retreat chronosequence is not linear, and after a quite rapid increase in carbon accumulation capacity in the first 150 years, in average 9 g C m−2 year−1, it slows down, taking place mainly in the belowground biomass components. Concurrently, the photosynthetic capacity peaks in the intermediate stage of ecosystem development. If confirmed by further studies on a larger scale, this study would provide evidence for a predominant effect of plant physiology over soil physical characteristics in the green-up phase after glacier retreat, which has to be taken into account in the creation of scenarios related to climate change and future land use.
Highlights
Air temperature is increasing globally and glacier retreat is among the most striking evidence of global change (Walker & Del Moral, 2003; Nakatsubo et al, 2005; Barry, 2006; Kozioł et al, 2014; Pepin et al, 2015), and this is evident in the Alps
Outlook: We found that the process of carbon accumulation along a glacier retreat chronosequence is not linear, and after a quite rapid increase in carbon accumulation capacity in the first 150 years, in average 9 g C m−2 year−1, it slows down, taking place mainly in the belowground biomass components
The linkage between net ecosystem exchange (NEE), gross ecosystem exchange (GEE) and Reco and site variables (AG and BG biomass, C and N, soil C and N, air temperature) was tested by multiple linear regression and by mixed models (Dataset S3) In the multiple linear regression assessment, we found that, over the whole season, the flux better explained by site conditions was Reco (80.57% variance explained by five regressors: C AG, dry weight (DW) BG, C BG, Nsoil and Tair,), while GEE and NEE variability was explained to a lower extent (54.82% and 41.19%, respectively) by a Multiple R-squared p-Value
Summary
Air temperature is increasing globally and glacier retreat is among the most striking evidence of global change (Walker & Del Moral, 2003; Nakatsubo et al, 2005; Barry, 2006; Kozioł et al, 2014; Pepin et al, 2015), and this is evident in the Alps. The glaciers in the Alps, as in other high mountain ranges and boreal zones, are generally retreating and leaving a wide surface of bare ground free from ice cover. This early stage soil is colonized by microbes and vegetation in a process of primary succession. To improve our understanding of the variables involved in the carbon accumulation in the different stages of primary succession, we conducted this research in three transects on the Matsch glacier forefield (Alps, N Italy) at an altitude between 2,350 and 2,800 m a.s.l. Methods: In three field campaigns (July, August and September 2014) a closed transparent chamber was used to quantify the net ecosystem exchange (NEE) between the natural vegetation and the atmosphere. If confirmed by further studies on a larger scale, this study would provide evidence for a predominant
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