Depth-specific response of soil microbial communities, below ground biomass and soil organic carbon stocks in a warming world
Abstract
Globally, often more than 50% of soil organic carbon is stored below 20 cm soil depth. Warming experiments mostly revealed increasing respiration in topsoils, and first studies indicate that also subsoils will respire more and release more greenhouse gases. However, environmental conditions in subsoils differ significantly from those found in topsoils, e.g. organic matter concentrations are lower, oxygen and nutrients are sparse, microbial communities differ. Thus, response of subsoil to warming and underlying processes need to be better understood if we are to accurately predict climate change responses of soils.
We sampled three pairs of control and warmed plots located on an Alfisol in a coniferous temperate forest in the Sierra Nevada, CA, USA. Heating rods and cables warmed the soil by +4 °C to 1 m depth over 4.5 years. We analyzed free extractable and hydrolysable lipids to assess the level of decomposition and detect changes of plant versus microbial inputs to soil organic carbon. To characterize microbial community composition, we used phospholipid fatty acids. The molecular-marker based proxies indicate a surprisingly strong depth-specific response of soil organic matter to warming. In the upper third (0-30 cm) of the warmed plots, we detected more above ground biomass-derived organic matter than in the control (indicated by the cutin/suberin markers). In contrast, in the lower third (below 60 cm soil depth), soil organic matter was more degraded (indicated by higher ratios of saturated vs. unsaturated fatty acids), we counted fewer fine roots,and there was more microorganism- compared to plant-derived organic matter (indicated by the average chain length of fatty acids). Furthermore, the microbial communityresponded to warming by a relative decrease of gram+ bacteria (suggested branched and straight chain fatty acids patterns). Overall, our results show that warming changed soil organic carbon composition, soil microbial communities, roots and below ground biomass in a depth-specific way. Remarkably, even deep (>60 cm) soil horizons rapidly responded to warming. For better predictions of how whole soils respond to warming we cannot simply extrapolate from our knowledge developed from topsoil observations.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B42D..04S
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0486 Soils/pedology;
- BIOGEOSCIENCES;
- 1622 Earth system modeling;
- GLOBAL CHANGE