Experimental design studying decomposition of oak litter
For each pair of the focal oaks, we sampled the litter at leaf fall by
gently shaking the branches and collecting the leaves before falling on
the ground to avoid contamination by soil microbes and arthropods prior
to the experimental treatment. Oak litter was air dried in the lab at
ambient temperature for at least 2 weeks. For each tree, four samples of
each oak litter (about 10 g in equivalent dry weight) were placed in
litter bags (25 cm × 15 cm) with 5 mm-mesh size allowing colonization by
microbes and soil fauna (Santonja et al . 2017). Moreover, for
each tree, five samples were weighted and oven-dried to estimate the
water content of the initial litter, i.e. (oven dry weight-air
dry weight)/air dry weight. This ratio permitted to estimate the
oven-dry weight equivalents of litter samples in the litter bags. Within
each pair of trees, litters from the high-phylogenetic isolation tree
were exposed below that tree and below the tree of low phylogenetic
isolation, and inversely for the low-phylogenetic isolation tree (Fig.
1c). Therefore, a given litter bag was characterized by phylogenetic
isolation of the oak from which the litter was sampled and the oak where
the litter was incubated, respectively phylogenetic isolation above- and
belowground PIA and PIB. Litter bags were posed at approx. 1 m from the
trunk of the focal tree, i.e. close enough to avoid impact from other
trees. Additional metal-mesh protection was used to avoid physical
disturbance by large mammals (wild boars, humans). We harvested the
litter bags twice, after 8 months and after 14 months. This gives 8
litter bags for each pair of oaks and a total of 88 litter bags.