Towards Vulnerability Minimization of Grassland Soil Organic Matter Using Metamodels

International audienceVulnerability is the degree to which a human or environmental system is likely to experience harm due to a perturbation or a stress. This paper aims at proposing a generic quantitative method for climate change vulnerability assessment and to illustrate it on the particular case of the steady-state soil organic matter (SOM) of grassland thanks to PaSim, a mechanistic biochemical model. Based on literature review, we first present a model of concepts related to climate change vulnerability, and then we give our numerical method for vulnerability assessment. We documented all the different steps of our approach (from building of the initial design of experiments, to assessment of vulnerability with adaptation, through generating response surfaces and searching for vulnerability minima with different optimization methods). This study showed that steady-state SOM content will globally increase in future and that their vulnerability will decrease (due to higher increase of average values compared to the increased variability). Moreover, the analysis of the found vulnerability minima suggests both a reduction of vulnerability of SOM of adapted system and an increase of the gain by adaptation

Soil Greenhouse Gases emissions in Mediterranean forage systems

Many studies on the impacts of soil management on Greenhouse Gases (GHG) emissions were carried out in the last years. However, field studies on GHG emissions in forage systems under semi-arid Mediterranean conditions are still limited. Modelling approaches are required for predicting the long term performances of Mediterranean grasslands under different environmental and management strategies, but so far very few attempts were made for these environments. The overall aim of the PhD dissertation was to analyse the processes and the management options that influence the soil C cycle and GHG emissions in two typologies of Mediterranean forage systems: extensively managed pastures and irrigated maize-based systems. Field experiments were carried out for both forage systems, while a modelling approach was undertaken only for the pastures. The PaSim model was assessed for its ability to simulate C exchanges in Mediterranean grasslands. A new model parameterization was derived for Mediterranean conditions from a set of ecophysiological parameters. The obtained results highlight the reliability of PaSim to simulate C cycle components in Mediterranean grasslands although some improvements are required. In the irrigated forage systems, soil GHG and the net Global Warming Potential were compared under different fertilization strategies, which showed contrasting impacts on GHG emissions, providing some insights on their different potential mitigation roles under Mediterranean conditions