Shifting leaf fall phenology disrupts ecosystem function

Leaf litter fall and processing in temperate streams is one of the most pervasive resource subsidies and ecosystem functions globally.¹^,²^,³ These subsidies are highly seasonally structured, yet their phenologies are shifting with climate change due to alterations of leaf senescence with global warming.⁴^,⁵^,⁶ As phenology and phenological changes are species specific,⁷ the order of senescence of different leaf species is shifting.⁸ While the effect of phenology on community assembly and species interactions is well known, its influence on ecosystem function (particularly through the resource subsidy order of arrival and the duration between arrivals of different subsidies) remains underexplored.⁹ Here, we tested how the order of arrival and exposition duration of resource subsidies affect ecosystem function. We conducted a mesocosm experiment manipulating the order of arrival of two contrasting leaf species (high- and low-nutrient content), testing the effects of subsidy order and duration on decomposition rates by an abundant aquatic shredder. Exposure duration and arrival order of leaf species strongly influenced combined leaf litter consumption. Earlier arrival of high-quality leaves enhanced feeding on low-quality leaves. Shifting leaf fall duration and order of arrival thus has the potential to impact carbon cycling, even when the combined resource quantity remains constant. Our study demonstrates that these changes can have direct consequences on ecosystem processes in the context of the globally important function of leaf litter processing, emphasizing the need for incorporating temporal ecological aspects to understand the climate change impacts on the functioning of ecosystems.¹⁰.