Litter decomposition in a temperate and a tropical stream: the effects of species mixing, litter quality and shredders

Abstract

Summary The current rapid decline in biodiversity has led to concerns about the consequences for stream ecosystem processes, one of which is the decomposition of leaf litter derived from riparian vegetation. We conducted field experiments in a tropical and a temperate stream to test for the effects of mixing leaf species differing in resource quality on the decomposition of leaf litter and on the colonisation of the litter by leaf‐shredding invertebrates. The effects of litter mixing were minor compared with the effects of litter quality and the presence or absence of shredders. Low shredder abundance in the tropical stream and poor quality of the tropical leaf species, particularly in terms of phosphorus content and toughness, were associated with low decomposition rates in the tropical compared with the temperate stream. This is especially true when considering the 20 °C temperature differences between the two streams. In the presence of shredders, the decomposition rate of a standard litter type, leaves of Alnus glutinosa, was 2.6‐fold faster in the temperate stream, whereas rates were similar when shredders were absent. This indicates that differences in environmental conditions other than temperature had a strong effect. Differences in water chemistry, such as higher concentrations of dissolved nutrients in the temperate stream, might account for this effect. In conclusion, despite a lack of clear effects of litter mixing on decomposition, our results highlight the importance of litter identity and environmental conditions for both microbial and shredder‐mediated litter decomposition, suggesting that changes in riparian vegetation and other stream characteristics will affect stream ecosystems in the face of widespread environmental change.

Leaf breakdown in a natural open tropical stream

“…Our results show that the invertebrate community was not responsible for the changes in leaf breakdown, consistent with studies in tropical streams Moretti et al, 2007). Some studies show that shredders have low abundance in tropical streams and emphasize the importance of microorganisms as major regulators of the process (Dobson et al, 2002;Gonçalves et al 2007, Li et al, 2009Boyero et al, 2012;Bruder et al, 2014). However, the opposite pattern has been identified in streams of temperate and subtropical zones and in high-altitude streams in the tropics, suggesting a greater importance of shredders (Graça, 2001;Yule et al, 2009;Encalada et al, 2010;Ferreira et al, 2012;König et al, 2014).…”

“…The concentrations of structural and secondary compounds in the litter of the two species studied here are higher than those reported for other species (Ardón et al, 2006;Gonçalves et al, 2006a;Ferreira et al, 2012;Bruder et al, 2014). Silva et al (2013) studied the cellulose, lignin and isotopic composition of 15 dominant species in the bogs in Serra do Espinhaço, southern Brazil, which are comprised primarily of moist grassland and semideciduous forest.…”

Environmental stressor gradients hierarchically regulate macrozoobenthic community turnover in lotic systems of Northern Italy

“…were more abundant in the cool streams. Similar findings were observed by Bruder et al (2014) when compared to litter decomposition and shredders activity between a tropical and a temperate stream with significantly different water temperatures.…”

Leaf traits induce the feeding preference of a shredder of the genusTriplectidesKolenati, 1859 (Trichoptera) in an Atlantic Forest stream, Brazil: a test with native and exotic leaves

“…For example, leaf toughness was negatively correlated with consumption rates of freshwater shredders (Li and Dudgeon 2008). Higher densities and biomass of shredders have been found on leaf patches with high nutritional quality (Larrañaga, Basaguren, Elosegi, and Pozo 2009;Graça and Cressa 2010;Garcia et al 2012;Bruder, Schindler, Moretti, and Gessner 2014).…”