Five-year decomposition effects on nutrient stocks of woody species in Mediterranean ecosystems

Long-term data on nutrient dynamics during woody debris (WD) decomposition in Mediterranean ecosystems are not sufficiently explored. This study aims to characterize the stocks of key nutrients (P, K, Ca, Na, and Mn) through a five-year litterbag experiment using ten types of WD, incubated in shrubland and woodland environments in Southern Italy under a Mediterranean climate. To explore relationships between nutrient dynamics and WD traits, thirty anatomical, chemical, and functional traits of undecomposed WD were assessed, including nutrient contents, cellulose and lignin contents, and organic chemical composition via ¹³C NMR analysis. After five years of incubation, the concentration and content of P, K, Ca, Na, and Mn in the WD were quantified. Mass loss after 5 years was higher in woodland (47.6%) than in shrubland (29.6%). Among the species, S. junceum, P. lentiscus and F. carica showed the highest mass losses while C. monspelliensis and E. arboreea recorded the lowest. Regarding nutrient dynamics, we observed net mineralization in 90 experimental cases, while nutrient immobilization occurred in only ten instances, i.e. five were for Mn, three for P, and two for Ca. Nutrient mineralization was significantly influenced by the type of WD and strongly correlated with the initial concentration of each nutrient. Different WD traits showed varying correlations with nutrient mineralization. For example, P release was negatively correlated with lignin concentration, K and Na release were positively associated with decay rates, Ca release was linked to labile C and the initial concentration of Mg, Mn, and Ca, while Mn mineralization was regulated by the availability of the carboxylic C fraction. This study provides the first long-term dataset on nutrient stocks during WD decomposition in Mediterranean ecosystems, highlighting the distinct roles of mineralization and immobilization based on nutrient type and WD traits. These findings have critical implications for modelling wood tissue decomposition processes in Mediterranean ecosystems.