Nonadditive Effects of Leaf Litter Species Diversity on Breakdown Dynamics in a Detritus-Based Stream

Abstract

Since species loss is predicted to be nonrandom, it is important to understand the manner in which those species that we anticipate losing interact with other species to affect ecosystem function. We tested whether litter species diversity, measured as richness and composition, affects breakdown dynamics in a detritus-based stream. Using full-factorial analyses of single- and mixed-species leaf packs (15 possible combinations of four dominant litter species; red maple [Acer rubrum], tulip poplar [Liriodendron tulipifera], chestnut oak [Quercus prinus], and rhododendron [Rhododendron maximum]), we tested for single-species presence/absence (additive) or species interaction (nonadditive) effects on leaf pack breakdown rates, changes in litter chemistry, and microbial and macroinvertebrate biomass. Overall, we found significant nonadditive effects of litter species diversity on leaf pack breakdown rates, which were explained both by richness and composition. Leaf packs containing higher litter species richness had faster breakdown rates, and antagonistic effects of litter species composition were observed when any two or three of the four litter species were mixed. Less-consistent results were obtained with respect to changes in litter chemistry and microbial and macroinvertebrate biomass. Our results suggest that loss of litter species diversity will decrease species interactions involved in regulating ecosystem function. To that end, loss of species such as eastern hemlock (Tsuga canadensis) accompanied by predicted changes in riparian tree species composition in the southeastern United States could have nonadditive effects on litter breakdown at the landscape scale.

Biodiversity at the plant–soil interface: microbial abundance and community structure respond to litter mixing

“…However, microbial communities often process mixtures of plant litter substrates (species and genotypes) at rates faster than expected from the average of the decomposition rates of the component litter types decomposing by themselves (Schweitzer et al 2005;LeRoy and Marks 2006;Hättenschwiler and Gasser 2005;Madritch et al 2006;Jonsson and Wardle 2008), a phenomenon termed a synergistic eVect or synergism [as opposed to an antagonistic eVect, which occurs less frequently (Wardle and Nicholson 1996;Bardgett and Shine 1999;Kominoski et al 2007)]. Despite the relevance of synergistic eVects of litter mixing to questions about biodiversity and ecosystem function and recent calls for more mechanistic studies (Gartner and Cardon 2004;, the mechanisms underlying synergistic decomposition remain elusive.…”

Consumer presence and resource diversity independently induce stability of ecosystem function in a Piedmont stream

“…One consequence is the loss of a specific leaf species from the detrital pool. Given there can exist substantial interspecific variation in litter resource quality (Ostrofsky 1997, Swan et al 2009), loss of leaf species diversity on organic matter processing is being increasingly studied (e.g., Kominoski et al 2007, Lecerf et al 2007, 2011, Schindler and Gessner 2009, Swan et al 2009). To date, there has been no explicit test of what the implications of litter species loss are for stability of ecosystem processing of detritus, nor the potential mechanisms.…”

“…The presence of P. gentilis was manipulated in a full factorial design with 11 leaf litter treatments (6 single-species, 4 five-species mixtures, and a mixture of all six species; Table 1). Diversity was reduced by removing in four mixture treatments each of the dominant overstory species as they each represent targets of realistic losses to forest communities (e.g., logging, invasive pests) and can overwhelmingly contribute to changes in breakdown dynamics (Kominoski et al 2007, Swan et al 2009, Lecerf et al 2011. A cage design was employed whereby a fixed mass of leaf litter was enclosed in a plastic cage with or without four individual P. gentilis larvae and allowed to break down for 39-40 days.…”

Influence of episodic acidification on leaf breakdown in neighboring streams of the western Adirondacks, USA

“…Empirical evidence for facilitation or inhibition of breakdown of species in mixtures is conflicting. Some studies have shown non-additive effects (McArthur et al 1994;Swan and Palmer 2004;Kominoski et al 2007), whereas others have not (Leff and McArthur 1989;Lecerf et al 2007). Taylor et al (2007) showed that the initial foliar chemistry strongly influenced whether breakdown rates were nonadditive.…”

“…where mixtures of different leaf species facilitate or inhibit breakdown of one or more species in the mixture). Some studies have shown that breakdown rates in mixtures are non-additive (McArthur et al 1994;Swan and Palmer 2004;Kominoski et al 2007), while others have shown limited or no evidence of non-additive effects (Leff and McArthur 1989;Lecerf et al 2007;Taylor et al 2007). It is not known, however, whether disturbances like acidic deposition augment or reduce non-additive effects.…”