Tree species composition shapes the assembly of microbial decomposer communities during litter decomposition

Tree species influence terrestrial ecosystem dynamics through litter decomposition, which is a complex process dependent on litter intrinsic properties, environmental conditions and species-specific microbial decomposer communities. We examined how the global-change driven forest succession from Scots pine (<em>Pinus sylvestris </em>L.) to Pyrenean oak (<em>Quercus pyrenaica</em> Willd.) may influence litter decomposition in a Mediterranean ecotone forest. <br> We performed a reciprocal experiment using litterbags in two neighbouring pure Scots pine and Pyrenean oak forests to assess the litter decomposition process from either pine (needles), oak (leaves) or a mixture 1:1 of needles and leaves. We determined successive changes in litter mass loss, carbon (C) and nitrogen (N) contents and microbial community structure by the phospholipid fatty acid method over a two-year period. The experiment involved litterbags left above the ground surface throughout a 24-month period. In late autumn 2013, senescent leaves and needles were handpicked from the branches of randomly selected trees in their respective Pyrenean oak and Scots pine stands. Collected senescent litter were oven-dried for two days at 50 °C to constant mass (Bärlocher 2005). Litterbags (20 cm x 20 cm, 1.5 mm x 2 mm fiberglass mesh at the top side, 500 μm polyester mesh at the bottom side) were filled with 10 g (± 1 mg) of senescent litter. In each forest stand, four replicated plots (35 m x 35 m) were stablished. In each plot, six triplets of litterbags (needle, leaves and mixed 1:1 needles and leaves) strained with a polyester rope were anchored to the soil surface with steel pegs to prevent their movement and to ensure a close contact with the forest floor. The triplets of litterbags were arranged in the direction perpendicular to the slope and separated by a mean distance of 5 m. Litterbags were placed in the field in April 2014 and collected every four months. At each sampling campaign, one triplet of litterbags per plot was randomly collected, placed in ice-cold coolers and immediately transported to the laboratory. In the lab, litter was cleaned, sorted and weighted. Needles and leaves from mixed species litterbags were manually separated for the subsequent analysis. Samples were split into three subsamples for the determination of the moisture, phospholipid fatty acid profile, carbon and nitrogen concentrations. Soil moisture was monitored monthly at 12 cm depth using a time-domain reflectometer (Field Scout TDR 100, Spectrum Technologies Inc., Aurora, USA). Soil temperature was recorded hourly using three sensors randomly installed in each forest stand at 10 cm depth (DS1922L Thermochron, iButtonLink LCC, Whitewater, USA). <br> Results published in Fernández-Alonso et al., 2022 – Plant and Soil. https://doi.org/10.1007/s11104-022-05593-0