Does nutrient limitation promote carbon storage in forest soils?

Soil organic carbon (SOC) is a major component of the global carbon (C) cycle.

Its vulnerability to disturbances and climate variations has been studied, but its response to altered nutrient availability is not well known.

Nitrogen (N) in particular is fundamental for the microbes that mediate the degradation of SOC, so that changes in N availability can alter the SOC balance.

Three microbial responses to N shortage are hypothesized: HP1) enzyme synthesis is slowed down, thus reducing C emissions; HP2) the efficiency of conversion of C into biomass (C-use efficiency, CUE) is reduced, which would maintain or increase C emissions; HP3) microbial internal recycling of N is increased.

Here we start by focusing on decomposition and ask: Q1) Which of these mechanisms is dominant, and what is their combined net effect on SOC?

We will then scale up to the ecosystem level, including plant-symbiont interactions, to ask: Q2) How does N limitation interplay with plant-microbe-soil interactions (priming)?

To this aim, we will harmonize existing stoichiometric theories under a common framework that accounts for all these different mechanisms, and synthesize literature data from microbial isolates to field scale, leveraging national soil surveys.

Theoretical explorations and meta-analyses will allow answering our questions, and specifically assessing the consequences of N addition (deposition, fertilization) and limitation (due to higher atmospheric CO2) on SOC stocks in forests.