Effects of two measures of riparian plant biodiversity on litter decomposition and associated processes in stream microcosms

Abstract

Plant litter decomposition is a key ecosystem process that can be altered by global changes such as biodiversity loss. These effects can be particularly important in detritus-based ecosystems, such as headwater streams, which are mainly fuelled by allochthonous plant litter inputs. However, experiments examining effects of plant diversity on litter decomposition in streams have not reached consensus about which measures of biodiversity are more relevant. We explored the influence of two of these measures, plant species richness (SR; monocultures vs. 3-species mixtures) and phylogenetic distance (PD; species belonging to the same family vs. different families), on leaf litter decomposition and associated processes and variables (nutrient dynamics, fungal biomass and detritivore growth), in a stream microcosm experiment using litter from 9 tree species belonging to 3 families. We found a negative effect of SR on decomposition (which contradicted the results of previous experiments) but a positive effect on fungal biomass. While PD did not affect decomposition, both SR and PD altered nutrient dynamics: there was greater litter and detritivore N loss in low-PD mixtures, and greater litter P loss and detritivore P gain in monocultures. This suggested that the number of species in mixtures and the similarity of their traits both modulated nutrient availability and utilization by detritivores. Moreover, the greater fungal biomass with higher SR could imply positive effects on detritivores in the longer term. Our results provide new insights of the functional repercussions of biodiversity loss by going beyond the often-explored relationship between SR and decomposition, and reveal an influence of plant species phylogenetic relatedness on nutrient cycling that merits further investigation.

Litter Quality Is a Stronger Driver than Temperature of Early Microbial Decomposition in Oligotrophic Streams: a Microcosm Study

“…We also found low microbial colonization and activity on this species, as shown in other studies [20,23]. Beech litter (Fagus sylvatica), here included in the lowest quality category, also decomposed slowly, as previously reported in field and laboratory studies [48,49], being specially neglected by detritivores [22]. Among the high-quality categories, F. insipida has been reported to decompose at rates similar to alder in temperate sites [49] or even higher in the tropics [50].…”

“…Beech litter (Fagus sylvatica), here included in the lowest quality category, also decomposed slowly, as previously reported in field and laboratory studies [48,49], being specially neglected by detritivores [22]. Among the high-quality categories, F. insipida has been reported to decompose at rates similar to alder in temperate sites [49] or even higher in the tropics [50]. As previously stated, forest changes can affect litter composition and decomposition rates, altering C flows [19], and this is not only a projection of climate change effects [13][14][15], but also natural forests suffering different sources of alternation [16][17][18].…”

Functional consequences of alder and oak loss in stream ecosystems

“…Sericostoma growth was highly variable within treatments and did not differ between the control and the scenarios, which contradicted our hypothesis but agreed with other studies in which detritivore growth did not respond to treatments of litter diversity (Lopez‐Rojo et al, 2020; López‐Rojo et al, 2019; Tonin et al, 2017) or quality (Larrañaga et al, 2020). It is possible that all the combinations provided enough resources for Sericostoma to achieve their maximum growth (Boersma & Elser, 2006), which was within the range reported elsewhere for Sericostoma spp.…”

“…However, under usual conditions, a great portion of leaf litter inputs only undergoes initial decomposition in the stream benthos before being transported downstream, incorporated into the sediments during periods of high sediment movement (e.g., spates), or emerged if the stream dries out (e.g., intermittent streams) (Graça et al, 2015;Tonin et al, 2021), making the initial litter decomposition phases the most relevant to assess (Pérez, Ferreira, et al, 2021). Sericostoma growth was highly variable within treatments and did not differ between the control and the scenarios, which contradicted our hypothesis but agreed with other studies in which detritivore growth did not respond to treatments of litter diversity (Lopez-Rojo et al, 2020;López-Rojo et al, 2019;Tonin et al, 2017) or quality (Larrañaga et al, 2020). It is possible that all the combinations provided enough resources for Sericostoma to achieve their maximum growth (Boersma & Elser, 2006), which was within the range reported elsewhere for Sericostoma spp.…”

“…It is possible that all the combinations provided enough resources for Sericostoma to achieve their maximum growth (Boersma & Elser, 2006), which was within the range reported elsewhere for Sericostoma spp. (our experiment: 1.52% day ‐1 on average; other studies: 0.75%–2.99% day ‐1 ; Friberg & Jacobsen, 1999; Lopez‐Rojo et al, 2020). Sericostoma growth might have been affected by species loss at higher detritivore densities or with lower litter availability, but this needs further exploration.…”