Funding: Basque Government (coordination), crowdfunding (field and lab work)

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A key question in contemporary ecology is how the loss of biological diversity affects ecosystem functioning. Plant litter decomposition is a fundamental ecosystem process with major consequences for the carbon cycle, but it is unclear how the loss of plant diversity affects decomposition rates. In a global-scale stream study, Boyero et al. (2016 Proc R Soc B 283: 20152664) examined decomposition rates of litter mixtures differing in phylogenetic diversity across latitudes and found that more diverse mixtures decomposed faster in the tropics, while less diverse mixtures decomposed faster at high latitudes. This suggested that different mechanisms might operate at different latitudes, possibly in relation to differences in biological assemblages that break down plant litter. Here, we explored this question through a coordinated experiment conducted at 40 stream sites distributed globally, where we quantified the decomposition of litter mixtures differing in phylogenetic diversity (low vs. high) and examined how differences between the decomposition of both litter mixture types varied across latitudes.