Nutrient addition hinders microarthropod-driven leaf litter decomposition in Patagonian woodlands

Aims: Global change threatens ecosystem functions, including those driven by soil fauna. In temperate forests, soil nutrients, litter quality, and microarthropods are essential players during litter decomposition. However, the impact of nutrient enrichment on the functional role of soil fauna remains poorly understood. Methods: We used a full factorial experiment to test the effects of nitrogen (N), phosphorus (P), and potassium (K) addition on litter decomposition through changes in soil conditions and litter quality. We incubated senesced leaves from fertilized and unfertilized control plots in litter bags with two different mesh sizes that included (2 mm) or excluded (45 µm) microarthropods. We assessed the interactive effects of nutrient addition and litter quality on microarthropod-driven decomposition using linear mixed-effects models. Results: Nutrient addition was a stronger predictor than litter quality for organic matter remaining in litter bags over time. While N addition strongly influenced litter quality, it did not affect microarthropod activity in decomposition. P addition suppressed decomposition when microarthropods were present but enhanced it when microarthropods were absent. K strongly influenced litter quality and regulated the effects of phosphorus on decomposition. Conclusions: Microarthropods may promote decomposition under conditions of limited nutrient availability in both litter and soil, potentially enhancing microbial activity. The responses of fungi and microbes to nutrient enrichment may explain the relatively modest effect of microarthropods on decomposition. Our study shows that nutrient enrichment in temperate forests may limit microarthropod participation in decomposition by possibly altering microsite conditions or affecting the availability of alternative food resources, thereby influencing carbon fluxes.