Environmental conditions modulate warming effects on plant litter decomposition globally

Empirical studies worldwide show that warming has variable effects on
plant litter decomposition, leaving the overall impact of climate change
on decomposition uncertain. We conducted a meta-analysis of 109
experimental warming studies across seven continents, using natural and
standardised plant material, to assess the overarching effect of warming
on litter decomposition and identify potential moderating factors. We
determined that at least 5.2 degrees of warming is required for a
significant increase in decomposition. Overall, warming did not have a
significant effect on decomposition at a global scale. However, we found
that warming reduced decomposition in warmer, low-moisture areas, while it
slightly increased decomposition in colder regions, although this increase
was not significant. This is particularly relevant given the past
decade's global warming trend at higher latitudes where a large
proportion of terrestrial carbon is stored. Future changes in vegetation
towards plants with lower litter quality, which we show were likely to be
more sensitive to warming, could increase carbon release and reduce the
amount of organic matter building up in the soil. Our findings emphasize
the connection among warming responses, macro-environment and litter
characteristics which can refine predictions of warming’s consequences on
key ecosystem processes and its contextual dependence.