What makes decomposition faster under conspecific trees? The factors controlling the magnitude of home-field advantage

The “home-field advantage (HFA)” for decomposition means that leaf litter
decomposes faster on soils under the conspecific species (i.e., the home
field) than on soils under different species (i.e., “away”). Many previous
studies have demonstrated the HFA, but the underlying mechanisms remain
unclear. We conducted a reciprocal litter-decomposition experiment using
two species with different leaf traits: Abies mariesii, an
evergreen conifer, and Fagus crenata, a deciduous broad-leaved tree. The
dominance of these species shifts along an elevation gradient with a
transition zone where both species coexist. In mixed forests of the
transition zone along the elevation gradient, we explored how the
magnitude of HFA between these two species was influenced by temperature,
soil properties, or leaf litter traits which could directly affect the
decomposition rate. The magnitude of HFA observed between the two species
varied widely from -3.89% to 28.3%. Our modeling showed that the magnitude
of HFA increased with decreasing soil pH and leaf litter N, i.e., in more
acidic soil and for less decomposable litter. Soil pH affected leaf litter
decomposition in the home plots of each species, whereas leaf litter N did
not. The magnitude of the HFA increased as the difference in soil pH
between the F. crenata and A. mariesii plots at the same elevation became
greater, but decreased as the difference in soil C became greater. Thus,
the response of leaf litter decomposition to environmental changes might
vary not only through direct effects of vegetation traits but also through
indirect effects of the HFA. This highlights the importance of considering
HFA for accurately predicting the response of local carbon and nutrient
cycles to climate change, particularly in communities where a replacement
of dominant species by others is expected due to climate change.