Biogeochemistry of Agroecosystems

Francisco Nájera De F.

PhD canditate

La Frontera University, Temuco, Chile
Supervisors:

  • Francisco Matus B. Chair Professor La Frontera University, Temuco, Chile

  • Michaella Dippold, Junior Professor of the Biogeochemistry of Agroecosystems in the Department of Crop Sciences (Faculty of Agriculture) of the Georg-August University Goettingen, Germany

  • Jens Boy, Assistant Professor Institute of Soil Science, Leibniz Universität, Hannover, Germany


Project

Effect of drying, rewetting and thawing on soil gas fluxes: understanding the response and underlying mechanisms

Climatic events such as drying/rewetting and freezing/thawing (D/R and T) cycles will likely be intensified in frequency and magnitude as proposed by global change modelling-scenarios. These events cause rapid changes in the biological and physical conditions of soil, stimulating microbial metabolism and mobilization of nutrients, thus causing the greenhouse gas (GHG) release from soil. A crucial part in this process occurs at macro-aggregates scale of soil. Macro-aggregate (> 250 µm) can be disintegrated (process called slacking), which exposes an intra particle particulate organic matter formerly physical protected to decomposition (iPOM). The new release POM is an additional C input to the microbial community, which might trigger other processes such as a priming effect (PE), i.e. the acceleration or retardation of native SOM decomposition due to fresh C input. Our study revisits the soil aggregates formation (Elliot, 1986) and hierarchy theory of soil aggregate turnover from Six et al. (2000), and on these Base we hypothesize that the intensification of D/R and T cycles, will increase the biodegradation of SOM, which in turn will increase the GHG emissions from soil. Furthermore, we hypothesize that the main driver of this process is the disruption of macroaggregates (> 250 µm) realising additional carbon. This will stimulates a priming effect associated to less protected SOM. The aim of this study is to determine the impact of D/R and T cycles on SOM biodegradation from POM pools and the additional GHG emission caused by the priming effect induced by macroaggreagate disintegration. Here we propose a laboratory experiment simulating D/R and T cycles in an incubation approach by adding 13C labelled organic matter to undisturbed cores of forest soil. These laboratory experiments will be cross-validated by field measurements at the original forest sites.