This infographic is primarily based upon a research paper: Microbial responses to warming enhance soil carbon loss following translocation across tropical forest elevation gradient (Nottingham et al., 2019). The infographic seeks to target A-level students and scientifically-informed public, to highlight the role of microbes in carbon cycling by case study. Thus, this infographic attempts to minimise the use of technical language whilst still conveying the information from the research paper.
The study takes place in the Kosñipata transect in the Peruvian Andes, with consistent annual precipitation and soil moisture and parent material across the elevation range (over 3000m). Therefore, the response of soil organic matter can be attributed to any change in temperature.
Soil cores were taken from high elevations (cool temperature regimes) and inserted into the soil at lower elevations (warm temperature regimes) to simulate climate warming. Subsequent investigation of the parameters of soil and its microbial community help to reveal the complex mechanisms that result in the apparent temperature sensitivity of the soil (Nottingham et al., 2015; 2019).
Pre-translocated soil samples were also investigated to reveal the long-term soil characteristics of different temperature ranges (Nottingham et al., 2015).
Tropical soils under cool conditions (Nottingham et al., 2015)
Pre-translocated soil cores from cool temperature regimes have a deep organic horizon. These soils are dominated by slow energy channel which results in soil organic carbon accumulation. These soils are also Nitrogen poor in part due to less Nitrogen fixation resulting from lower temperatures. Any subsequent increase in microbial nitrogen demand will initiate the mining of soil organic matter to access the nutrients.
Tropical soils under warm conditions (Nottingham et al., 2015)
Pre-translocated soil cores from warm temperature regimes in lowland forests have a very shallow organic horizon with only a small portion of labile carbon compounds. These soils are dominated by microbial communities that are associated with the fast energy channel causing a fast turnover of labile soil carbon, resulting in low soil organic carbon accumulation.
Results (Nottingham et al., 2019)
Results of the soil translocation experiments indicate a 3.86% decline in soil carbon for each 1°C increase over 5 years. Associated changes in microbial community composition, increased microbial carbon use efficiencies, increase activities of enzymes and an increase in soil respiration rates also occurred after translocation down elevation.
The role of microbes (Nottingham et al., 2019)
An increase in temperature due to translocation resulted in a change in microbial community physiology. An increase in carbon use efficiency is associated with increased microbial biomass and increased enzyme synthesis, as well as an increase in the activities of enzymes. These changes stimulate an increase in overall microbial respiration and thus an increase in soil organic matter degradation. The changes in microbial physiology may result from acclimation (a physiological response from microbes), adaptation and shifts in the composition of the soil microbe community (Nottingham et al., 2019).
Further investigation needed
This research predominantly investigates the warming response from cooler tropical forest soils. This excludes any further warming response of lowland tropical forests which cover a high proportion of the land area of tropical forests (Nottingham et al., 2015; 2019).
Having graduated in Environmental Geoscience from the University of Birmingham in 2019, Sam is looking forward to starting his PhD in October 2020. Sam’s PhD aims to study how microbial and mineralogical mechanisms together determine the stabilization and long-term persistence of soil organic carbon.
Organisation: Lancaster University