Phosphorus and micronutrient dynamics during gymnosperm and angiosperm litters decomposition in temperate cold forest from Eastern Canada

- We investigated P and micronutrients dynamics during litter decomposition.
- We studied decomposition in angiosperm and gymnosperm litters.
- Biomass loss was comparable for both litter types.
- The concentration of most studied elements increased during decomposition.
- P and Mo concentration decreased during decomposition in gymnosperm litter.

Molybdenum (Mo) and phosphorus (P) limitation and co-limitation of asymbiotic dinitrogen (N2) fixation has been reported in many ecosystems, from tropical to boreal. However, the mechanisms leading to these limitations remain elusive. In cold temperate forests Mo and P limitation of asymbiotic N2 fixation has been observed in gymnosperm litter but not in angiosperm litter suggesting an important role of the vegetative cover. In gymnosperm litters, P and Mo limitation is characterized by a strongly seasonality; P limitation was observed early in the growing season while Mo limitation appears midway in the growing season. This discrepancy between gymnosperm and angiosperm litters and the strong seasonality suggest that the quality of the litter and decomposition dynamics play an important role in the emergence of Mo and P limitation in gymnosperm litters from cold temperate ecosystems. While the dynamics of macronutrients (i.e. C, N) during decomposition are well documented, our understanding of micronutrient (i.e. trace metals) dynamics during litter decomposition remains limited. Here, we measured nutrient concentrations (P, Mo and others) during litter decomposition in various angiosperm and gymnosperm litters and their combinations (2 and 4 species) using litter bags. Results showed that angiosperm litter achieves higher nutrient concentrations (P and metals) than gymnosperm litter. The concentration of most elements increased in both litter types over a 6-month period of decomposition (Al, Co, Cu, Fe, Mn, V, Ti, and Zn), with the exception of P and Mg which decreased over time. During decomposition, the concentration of Mo increased by ~ 300% in angiosperm litter but decreased by ~ 50% in gymnosperm litter. Together, these results suggest that the litter can concentrate metals from the surrounding environment (i.e. soil and atmospheric deposition) except for Mo in gymnosperm litter. Litter quality (nutrient concentration) and nutrient dynamics during litter decomposition likely play an important role in P and Mo limitation of asymbiotic N2 fixation.