Opposing Effects of Plant-Community Assembly Maintain Constant Litter Decomposition over Grasslands Aged from 1 to 25 Years

Abstract

word count/Total word count 250/4545, number of figures/tables/appendices 4/0/3 13 Highlights : 14 • Plant-community assembly impacts plant afterlife traits and decomposer communities 15 • Plant-community assembly drives litter decomposition at a given successional stage 16 • Effects of traits and decomposers on decomposition mutually cancel out each other 17 Short title: Community assembly drives litter decomposition 18 19 Corresponding author: Lou Barbe (+33 6 67 44 06 56) 20 Authors' contributions: All authors contributed to the conception of the experiment and the data 21 collection. LB analyzed the data, with help of AP, CM and VJ. LB wrote the manuscript, with help of 22 all authors. 23 24 1 A c c e p t e d m a n u s c r i p t SUMMARY 25Litter decomposition is central to ecosystem functioning and depends, under constant abiotic 26 conditions, on litter quality and decomposer activity. During the assembly of a plant 27 community following disturbance, litter quality is expected to decrease, due to an increasing 28 proportion of resource-conservative species, whereas decomposer activity is expected to 29 increase, due to the establishment of decomposer populations and their response to local 30 vegetation ("Home-Field Advantage", HFA). To date, the combined effect of these processes 31 remains poorly understood. We studied 27 semi-natural grasslands in western France, ranging 32 from 1 to 25 years since last cultivation. We measured the functional composition of plant 33 communities using litter traits (Specific Leaf Area, Leaf Dry Matter Content, C:N ratio, 34 phenolics), characterized the entire community of decomposers (macrofauna, mesofauna, 35 microbes) and performed reciprocal litter transplants to quantify HFA. We found that, overall, 36 decomposition was rapid, and HFA was not evident. While there was substantial among-37 grassland variation in decomposition and HFA, neither changed with grassland age. Litter 38 quality and decomposer efficiency also remained, overall, unchanged. However, grassland 39 age determined all measured litter traits, and caused soil microbial C:N ratio to decline. While 40 these changes impacted decomposition individually, together they cancelled out each other, 41 resulting in constant decomposition across the chronosequence. Our results suggest that 42 processes driving decomposition differ during grassland succession, and suggest that HFA 43 may be lower in communities with high litter quality. Moreover, simultaneous assembly 44 processes have opposing, and therefore stabilizing effects on decomposition, possibly 45 explaining the outstanding resilience of primary production in temperate grassland 46 ecosystems.47 Key-words: plant-community assembly, decomposers and detritivores, Home-Field 48 Advantage, grasslands, litter decomposition, plant functional traits 49 2 A c c e p t e d m a n u s c r i p t 50 The decomposition of plant litter is one of the main bottlenecks regulating carbon storage and 51 nutrient cycling in terrestrial ecosystems (Swift and othe...

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