What controls forest litter decomposition? A coordinated, distributed
teabag experiment across 10 mountains
Abstract
Forest litter decomposition is considered as an essential ecosystem
process affecting carbon and nutrient cycling in mountains. However,
there exists high uncertainty in accurately estimating the contribution
of litter decomposition to terrestrial ecosystems, largely due to the
incomparability of different studies and the data limitation in
microclimate and non-climatic factors at spatially matched scales. Here
we used the tea bag index (TBI) as a standardized protocol to evaluate
spatial variations in forest litter decomposition rate (k) and
stabilization factor (S) across 10 mountains spanning a wide range of
subtropical and tropical forests. Based on the coordinated experiment of
6,864 teabags in 568 sampling sites along elevations, we evaluated the
importance of 10 environmental factors covering soil microclimate,
edaphic properties, plant diversity, and topography on k and S by using
model averaging and linear-mixed effects models. Of the 10 mountains, we
found a consistently decreasing pattern of k and an increasing pattern
for S along elevations. And the significant effect of k with elevation
was mainly found in the western and northmost mountains, while the
effect of S occurred in the western and southernmost mountains. For
microclimate, there was a general importance of soil temperature (coef.
= 0.48) and temperature variation in the growing season (coef. = 0.36)
in k, and soil temperature (coef. = -0.46) and moisture variation on S
(coef. = -0.36). The dominant role of soil microclimate was mainly found
in western mountains with relatively cold environments. For non-climatic
drivers, a significant effect of tree diversity on k and a negative
correlation of edaphic and topography with S in the western and southern
mountains were detected. These findings provide a general understanding
of spatial variations of driving factors in forest litter decomposition
and highlight a dominant control of soil microclimate in cold forests in
high elevations and latitudes.