Measurements of litter decomposition and litter traits
After the extraction of soil arthropods, litter was oven dried at 65 °C
to weight constancy and weighed at 0.1 g. The same was done with litter
that had not been exposed. The mass loss was then calculated as
(pre-exposure – post-exposure)/ pre-exposure. Oven-dried litter was
grinded using a ball mill. Carbon and Nitrogen concentrations were
determined by using an elemental analyser (N1500, Carlo Erba, Milan,
Italy). The changes in C and N concentrations were calculated in the
same way as for mass loss. A decrease of C concentration reflects rapid
decomposition. Inversely, an increase of N concentration reflects an
accumulation of N in the litter due to decomposition, improving resource
conditions for plants. We refrained from using changes of absolute C or
N values to avoid bias from among-site variation of C or N. For
instance, high-N sites would always show higher absolute changes of N
than low-N sites. Subsequently, leaf carbon isotope was analyzed using
an isotope ratio mass spectrometer (Isoprime100; Isoprime Ltd, UK) and
the absolute atom percentage of carbon isotope was used for further
analysis. Total phenolic concentration of initial litter was measured
colorimetrically using the method of Santonja et al . (2015) with
gallic acid as a standard. Leaf powder samples (250 mg) were suspended
in 20 mL of a 70% aqueous methanol, shaken for 1 h and then filtered
(0.45 µm filter). Filtered extracts (0.25 mL) were mixed with 4 mL of
distilled water, 0.5 mL of saturated aqueous
Na2CO3 and 0.25 mL of Folin-Ciocalteu
reagent. After 60 min, phenolic concentrations were determined at 765 nm
on the same UV/Vis spectrophotometer (Biomate 3, Thermo Electron
Corporation®) and expressed as mg of gallic acid equivalent.
g-1 DW.