Litter decomposition in Afrotropical streams: Effects of land use, home-field advantage, and terrestrial herbivory

Land use can strongly affect litter decomposition, a key ecosystem process in low-order streams. Recent evidence suggests that additional drivers of decomposition rates may include: 1) home-field advantage, whereby litter decomposes faster near the site of litter origin than at distant sites; and 2) terrestrial herbivory, whereby herbivore damage to leaves induces plant defenses that influence subsequent decomposition in streams. To compare the relative importance of these 3 potential drivers of decomposition rates, we conducted a decomposition experiment in Afrotropical streams and manipulated land use (farm vs forest sites), home-field advantage (leaves decomposing in streams near vs away from site of leaf collection), and terrestrial herbivory (using leaves varying in extent of herbivore damage). We measured decomposition in both fine-mesh and coarse-mesh litter bags to compare drivers of microbial vs invertebrate-mediated decomposition. Microbial decomposition in fine-mesh bags was unaffected by the experimental treatments. In coarse-mesh bags, land use was the only factor strongly associated with decomposition rate, most likely because invertebrate shredders are absent from farm sites. We conclude that home-field advantage and terrestrial herbivory have relatively-weak effects on litter decomposition rates in Afrotropical streams compared to a major anthropogenic disturbance such as agricultural land use.