Magnesium addition increases microbial metabolic efficiency during decomposition of Patagonian leaf litter

There is increasing evidence of a positive relationship between cation concentration in plant litter and its decomposition, particularly in the Patagonian forests where magnesium (Mg) is the strongest predictor of leaf litter decomposition. We aimed to evaluate the role of Mg in litter decomposition and the possible mechanisms behind its effect. We proposed that Mg increases decomposition by promoting microbial biomass and enzymatic activity, as Mg regulates microbial cell growth and functions as an enzymatic cofactor.

We conducted two experiments involving Mg addition using leaf litter of dominant native tree species and soil from the Patagonian forest. One was a 9-month outdoor litterbag decomposition study with Nothofagus antarctica litter in soil containers, while the other was a laboratory experiment with Nothfagus antarctica and Maytenus boaria litter.

In the litterbag decomposition study, Mg addition increased mass loss by 22% (p = 0.03) and 20% (p = 0.003) after 92 and 160 days of incubation, respectively. Also, Mg addition increased accumulated potential β-glucosidase activity by 63% (p = 0.0003) and 23% (p = 0.01) after 92 and 160 days of incubation, respectively. In the laboratory experiment, Mg addition increased microbial biomass carbon by 22% (p = 0.0317) and decreased the microbial metabolic quotient by 23% (p = 0.0165) in both litter species.

Our study delves deeper into the positive correlation between Mg concentration and litter decomposition documented in previous field studies and provides experimental evidence for an increase in microbial metabolic efficiency in response to Mg addition during litter decomposition.