Similarities and differences in the sensitivity of Soil Organic Matter (SOM) dynamics to biogeochemical parameters for different vegetation inputs and climates

TL;DR

This study investigates how biogeochemical parameters influence Soil Organic Matter (SOM) dynamics and greenhouse gas emissions across different ecosystems and climates using a detailed mechanistic model.

Contribution

It introduces a comprehensive sensitivity analysis of biogeochemical parameters affecting SOM and GHG emissions in diverse ecosystems, highlighting key controlling factors.

Findings

GHG emissions and SOM are highly sensitive to aerobic bacteria mortality.

Forests exhibit higher CO2 emissions due to greater dissolved SOM.

Soil N availability is mainly driven by vegetation inputs in forests and atmospheric fixation in grasslands.

Abstract

The biogeochemical complexity of environmental models is increasing continuously and model reliability must be reanalysed when new implementations are brought about. This work aim to identify influential biogeochemical parameters that control the Soil Organic Matter (SOM) dynamics and greenhouse gas emissions in different ecosystems and climates predicted by a physically-based mechanistic model. This explicitly accounts for four pools of organic polymers, seven pools of organic monomers, five microbial functional groups, and inorganic N and C species. We first benchmarked our model against vertical SOM profiles measured in a temperate forest in North-Eastern Bavaria, Germany (Staudt and Foken, 2007). Next, we conducted a sensitivity analysis to biogeochemical parameters using modified Morris indices for target SOM pools and gas emissions from a tropical, a temperate, and a semi-arid grassland in Australia. We found that greenhouse gas emissions, the SOM stock, and the fungi-to-bacteria ratio in the top soil were more sensitive to the mortality of aerobic bacteria than other biogeochemical parameters. The larger CO2 emission rates in forests than in grasslands were explained by a greater dissolved SOM content. Finally, we found that the soil N availability was largely controlled by vegetation inputs in forests and by atmospheric fixation in grasslands