Relative effects of climate and litter traits on decomposition change with time, climate and trait variability

Climate and litter quality drive litter decomposition, but there is
currently little consensus on their relative importance, likely because
studies differ in the duration, the climatic gradients, and variability in
litter-trait values. Understanding these drivers is important because they
determine the direct and indirect (via vegetation composition) effects of
climate change on decomposition and thereby on carbon and nutrient
cycling. We studied how microclimate (soil moisture and temperature) and
litter traits interactively affect litter mass loss, by using a reciprocal
litter translocation experiment along a large climatic gradient in Chile.
We followed decomposition for two years and used 30 plant species with a
wide spectrum of functional-trait values. Litter traits had a strong
impact on litter decomposition across the gradient, while an increase in
decomposition with soil moisture was observed only in the wettest
climates. Overall, soil moisture increased considerably in importance,
relative to trait effects, at later decomposition stages, from ca. 15% of
the importance of traits after 3 and 6 months to ca. 110% after 24 months.
Moreover, analyzing subsets of the 30 species showed that trait effects on
litter decomposition gained in importance when including a greater
variation in trait values. Synthesis. The relative effects of litter
traits and climate on decomposition depend on the ranges in climate and
litter traits considered and change with time. Our study emphasizes the
critical role of representative ranges in climate and functional trait
values for understanding the drivers of litter decomposition and for
improving predictions of climate-change effects on this important
ecosystem process.