A Biogeochemical analysis of Mediterranean ecosystems and the response to nitrogen deposition: an insight on the carbon and nitrogen cycle in Mediterranean Ecosystems

The carbon (C) and nitrogen (N) cycles have been drastically altered by humans as result of the increasing demand for energy, raw material and food. Combustion of fossil fuels and increasing industrial activities are linked with the emission of carbon dioxide (CO2), which is largely responsible for the rise in atmospheric CO2concentration during the past 50 years. At the same time, there has also been an increase in the concentration of oxidized (NOX) and reduced (NH3) nitrogenous compounds in the atmosphere, largely attributable to vehicular traffic and agricultural practice. In dry and hot conditions of the Mediterranean, the interaction of reactive N with plants and soils didn’t receive much attention. The thesis strongly contributes to fill this knowledge gap with research on the belowground part of the cycles. The work has been part of NitroMed, exciting new network of N deposition experiments in the Mediterranean. More specifically this PhD dissertation bring an insights to the role of N emission in Mediterranean basin through a review of existing literature (ch2), an improved understanding on the role of biocrusts in dryland ecosystem functioning (ch3), an in-depth understanding on how increased N deposition can first stimulate and in the longer term (or at higher deposition rates) break organic matter mineralisation in soils (ch4) and an elegant proposal of mechanistic understanding on N deposition effects on soil biological activity and C mineralization (ch5).