How detritivores, plant traits and time modulate coupling of leaf versus woody litter decomposition rates across species

1. Plant functional traits are increasingly used to understand
ecological relationships and (changing) ecosystem
functions. For understanding ecosystem-level biogeochemistry, we need to
understand how (much) traits co-vary between different
plant organs across species, and its implications for litter
decomposition. However, we do not know how the degree of
synchronous variation in decomposition rates between
organs across species could be influenced by different keystone
invertebrates decomposing different senesced plant organs,
especially in warm-climate forests. Here we asked
whether interspecific patterns in wood and leaf decomposition
rates and in the spectra of resource
economics traits underpinning them,
co-vary across woody species; and how (much) the
keystone invertebrate decomposers of the litter of these organs
enhance or lower such co-variation of decomposition
rates through time.  2. We
addressed these questions through an 18-month “common-garden”
decomposition experiment using leaf, twig and branch litter of 41 woody
species in two distant subtropical forest sites in east China. We
quantified the effects of leaf,
twig, and branch functional traits and their
respective key invertebrates (moth larvae, termites) on the decomposition
rates of those organs.  3. Interspecific
variation in wood traits was partly decoupled from that in leaf
traits across species, while strong coupling was found between twigs and
branches. The co-variation between leaf and woody organ
decomposition rates was altered dynamically through the
shifting activities of the key decomposers, which created
non-linear relationships of invertebrate litter consumption as a function
of species rankings along the resource economic trait spectra of leaves
and branches. 4. The deviations from coupling of decomposition
rates between organs were likely caused by combinations of three
mechanisms: (1) (de-)coupling between organs of other traits, not commonly
considered in resource economics spectra (e.g., resins) (2) leaf
and wood decomposers having specific diet requirements, and (3) temporal
patterns of the decomposers’ activity. 5. Synthesis. Our study
highlights the importance of considering the different ways by
which invertebrate detritivores drive decomposition
processes through time. Under the ongoing biodiversity
decline, future research would benefit from a better understanding
of the role of the dynamic interactions between
detritivore activities and plant functional traits on the carbon turnover
in ecosystems.