Decomposition constraints in acidified oak forests impacted by N deposition: a litterbag study on microarthropods

Nitrogen deposition causes soil acidification, which has been shown to slow down decomposition of organic matter in old oak forest stands. To restore this critical ecosystem function, we need to understand the current diversity and functional roles of decomposer organisms. We conducted a 21-month litterbag study in a Quercus robur forest in the Netherlands, using 6 different leaf treatments. These included leaves from Populus tremula as an easy degradable leaf type or Quercus robur leaves. Furthermore, leaves from each species originated from 3 different seasons (spring, summer, autumn). We extracted microarthropods from the litterbags, identified them to species level, and assigned feeding guilds to understand different stages of species establishment of microarthropods during decomposition. We found differences in decomposition rates between treatments, with spring leaves from Populus tremula decomposing the quickest and autumn leaves from Quercus robur decomposing the slowest. Feeding guild composition also differed significantly between leaf treatments; easily decomposable Populus leaves harboured more herbivorous grazers, while more recalcitrant Quercus leaves supported greater species diversity and abundance of fungivores, especially in autumn leaves, which had the overall highest microarthropod abundances. These patterns indicate that microarthropod community composition is consistent with different leaf chemistry. • Foreign leaves decomposer quicker than resident leaves • Litterbag study with all microarthropods identified to species level and feeding guilds assigned • Herbivores mediate early-stage decomposition; fungivores mediate late stage. • Highest species richness (fungivores) and overall microarthropod abundance entertained by Quercus leaves than Populus leaves