Experimental shading control on litter decomposition in tropical streams via the priming effect

Abstract The priming effect is defined as the alteration of the recalcitrant C decomposition by the labile C input into the ecosystem. This process is broadly accepted in soil, but the few studies investigating the priming effect in streams were mostly conducted in laboratory or mesocosm, which limit the conclusions from an ecosystem scale perspective. Here, we investigate the importance of the priming effect for decomposition in a field experiment using artificial shading in Brazilian Cerrado biome streams. Our hypothesis is that the higher periphytic algae accrual in reaches without cover (non-shaded sections) would lead to a higher microbial and invertebrate-mediated litter decomposition due to the increased priming effect. We observed that the non-shaded sections had higher periphytic algae quantity than the artificially shaded sections. We showed that the microbial and invertebrate-mediated litter decomposition was reduced in non-shaded sections—implying that priming was negative, although this difference was not consistent among incubation times. Also, the increase in periphytic algae quantity reduced the litter mass loss mediated by microorganisms in one of the incubation times, which partly supports these results. Our findings indicate that through bottom-up stimulation of periphytic algae on consumers, priming effect can reduce litter decomposition in tropic streams.