Leaf traits drive plant diversity effects on litter decomposition and FPOM production in streams.

Naiara López-Rojo,Luz Boyero,Ana Basaguren,Jesús Pozo,Aingeru Martínez,Javier Pérez,Cristina Armas

doi:10.1371/journal.pone.0198243

Naiara López-Rojo, Luz Boyero + Show 5 more

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https://doi.org/10.1371/journal.pone.0198243

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Abstract

Biodiversity loss in riparian forests has the potential to alter rates of leaf litter decomposition in stream ecosystems. However, studies have reported the full range of positive, negative and no effects of plant diversity loss on decomposition, and there is currently no explanation for such inconsistent results. Furthermore, it is uncertain whether plant diversity loss affects other ecological processes related to decomposition, such as fine particulate organic matter production or detritivore growth, which precludes a thorough understanding of how detrital stream food webs are impacted by plant diversity loss. We used a microcosm experiment to examine the effects of plant diversity loss on litter decomposition, fine particulate organic matter production, and growth of a dominant leaf-shredding detritivore, using litter mixtures varying in species composition. We hypothesized that plant diversity loss would decrease the rates of all studied processes, but such effects would depend on the leaf traits present in litter mixtures (both their average values and their variability). Our findings partly supported our hypotheses, showing that plant diversity loss had a consistently negative effect on litter decomposition and fine particulate organic matter production (but not on detritivore growth) across litter mixtures, which was mediated by detritivores. Importantly, the magnitude of the diversity effect and the relative importance of different mechanisms underlying this effect (i.e., complementarity vs. selection) varied depending on the species composition of litter mixtures, mainly because of differences in litter nutritional quality and trait variability. Complementarity was prevalent but varied in size, with positive selection effects also occurring in some mixtures. Our results support the notion that loss of riparian plant species is detrimental to key stream ecosystem processes that drive detrital food webs, but that the magnitude of such effects largely depends on the the order of species loss.

Highlights

Human activities are altering freshwater ecosystems worlwide, with significant impacts on biological communities and ecosystem processes [1]
We examined the differences in initial leaf traits (N and P concentrations, SLA, toughness and ash concentration) across plant species and across 3-spp litter mixtures with linear models using the gls function and restricted maximum likelihood (REML) method in the ‘nlme’ R package, with plant species as a fixed factor, followed by Tukey pairwise multiple comparisons using the glht function of the ‘multcomp’ package [18]
We explored whether litter decomposition, fine particulate organic matter (FPOM) production and detritivore growth decreased with diversity loss from 4 to 1 species in the ACQI litter mixture, with linear models followed by pairwise multiple comparisons

Summary

Introduction

Human activities are altering freshwater ecosystems worlwide, with significant impacts on biological communities and ecosystem processes [1]. Together with mechanical fragmentation, lead to the production of fine particulate organic matter (FPOM), which provides an important resource for other consumers such as collector-gatherers and filter-feeders [5, 6], supporting invertebrate and vertebrate predators [3]. Understanding how these key processes are affected by biodiversity loss is important to predict alterations in stream ecosystem functioning [7], given the current high rates of extinction [8]

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