Functionally or phylogenetically distinct neighbours turn antagonism among decomposing litter species into synergy

Abstract

Plant species coexisting in direct contact produce patches of mixed litters. Mixing litter sometimes synergistically accelerates and sometimes antagonistically decelerates litter decomposition, but we insufficiently understand why. Here, we hypothesize that antagonism or synergy within a mixed‐litter patch depends on the neighbouring litter matrix. Specifically, phylogenetical or functional dissimilarity within neighbouring litter, or among patch and neighbouring litter, may favour complementarity and thereby within‐patch synergy. From a pool of 20 grassland species, we created 120 mixed‐litter patches of two species, and exposed these patches to neighbourhoods in long‐term grassland mesocosms of different functional and phylogenetic compositions. We found 60% less (antagonism) to 80% more (synergy) decomposition than expected from single‐species litters. Functionally similar, and grass‐dominated, mixed‐litter patches decomposed most synergistically. Synergy was most strongly favoured by phylogenetic distance among neighbours and functional dissimilarity between neighbours and patch. Synthesis. Our results show that the relationship between biodiversity and ecosystem functioning was context‐dependent. We suggest that the coexistence of grasses and the formation of phylogenetically diverse, functionally distinct, patchy vegetation may be reinforced by synergistic nutrient recycling.

Synergistic effects: a common theme in mixed‐species litter decomposition

“…Although experiments concerning the mixture effects on litter decomposition rates have been conducted in numerous individual studies, the conflicting results have hampered any possibility to draw general conclusions (Li et al, 2016). Most of conflicts could mainly result from the significant differences of influencing factors related to litter decompositions in experimental design (Barbe et al 2018, Leroy et al 2018, Zhao et al 2019. Thus far, those various studies on mixed decomposition were all performed in different ecosystems across different climate regions with decomposition durations varying from several weeks to even as long as several years.…”

Functional and phylogenetic diversity promote litter decomposition across terrestrial ecosystems

“…Plant phylogenetic diversity can also be an indicator of complementarity effects in litter mixtures (Barbe et al, 2018). Closely related species in phylogeny tend to have similar functional properties, including their litter decomposition rate (LeRoy et al, 2020), which signifies their occupation of similar niches.…”

Associational decomposition: After‐life traits and interactions among decomposing litters control during‐life aggregation of plant species

“…We collected all litterbags 6 weeks later, when they reached 30%-60% mass loss. Such high mass loss results from the humid and relatively warm, frost-free winter in the study region which increases decomposer activity (Barbe et al, 2018). We cleaned the litter by hand and oven-dried it for 3 days at 65°C.…”

“…These after-life interactions among plants could represent a dynamic 'litter-interaction filter' for plant community assembly, equivalent to other biotic interaction filters that control assembly (Dwyer & Laughlin, 2017;Loughnan & Gilbert, 2017). Barbe et al (2018) recently found that decomposition synergy is strongest among grasses. Combined with the present result of facilitation of aggregation through synergistic interactions during decomposition, this might contribute to explaining why grasses coexist so often despite being functionally similar, and why their evolutionary success was particularly strong (Cahill et al, 2008;Linder et al, 2018).…”

“…High quality of litter mixture may also depend on during-life traits related to resource acquisition and conservation, since dead tissues often inherit the properties of living tissues (Aerts, 1996): in particular, high during-life specific leaf area (SLA) and low low leaf dry matter content (LDMC) generally correspond to more nutrient-rich litter tissues for detritivores and decomposers (Pakeman, Eastwood, & Scobie, 2011;Quested et al, 2007;Santiago, 2007). Last, the dissimilarity of after-life and during-life traits may trigger synergistic interactions during litter-mixture decomposition: more dissimilar traits provide a larger range of resources for generalist detritivores and decomposers or for a larger range of specialist decomposers, which are more efficient than when they decompose monospecific litters (Barbe et al, 2018;Gessner et al, 2010;Tardif & Shipley, 2015). Overall, heterospecific individuals producing a litter mixture of high quality (due to physical or chemical traits ensuring high decomposability) or a litter mixture which decomposes faster due to after-life synergistic interactions, might aggregate spatially (Figure 1).…”