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The Biological Field Station of Paimpont (Station Biologique de Paimpont, SBP), owned by the University of Rennes and located in the Brocéliande Forest of Brittany (France), has been hosting student scientific research and field trips during the last 60 years. The study area of the SBP is a landscape mosaic of 17 ha composed of gorse moors, forests, prairies, ponds and creeks. Land use has evolved over time. Historical surveys by students and researchers focused on insects and birds. With this study, we aimed to increase the range of taxa observations, document changes in species composition and landscape and provide a basis for interdisciplinary research perspectives. We gathered historical data, implemented an all-taxon biodiversity inventory (ATBI) in different habitats of the SBP study area, measured abiotic factors in the air, water and soil and performed a photographical landscape observation during the BioBlitz held in July 2017. During the 24 h BioBlitz, organised by the SBP and the EcoBio lab from the University of Rennes and the French National Center of Scientific Research (CNRS), different habitats were individually sampled. Seventy-seven experts, accompanied by 120 citizens and 12 young people participating in the European Volunteer Service, observed, identified and databased 660 species covering 5 kingdoms, 8 phyla, 21 classes, 90 orders and 247 families. In total, there were 1819 occurrences including records identified to higher taxon ranks, thereby adding one more kingdom and four more phyla. Historical data collection resulted in 1176 species and 4270 occurrences databased. We also recorded 13 climatic parameters, 10 soil parameters and 18 water parameters during the BioBlitz. Current habitats were mapped and socio-ecological landscape changes were assessed with a diachronic approach using 32 historical photographs and historical maps. The coupling of historical biodiversity data with new biotic and abiotic data and a photographic comparison of landscape changes allows an integrative understanding of how the SBP changed from agriculturally-used land to a managed natural area within the last 60 years. Hence, this BioBlitz represents an important holistic sampling of biodiversity for studies on trophic webs or on trophic interactions or on very diverse, but connected, habitats. The integration of social, biotic and abiotic data opens innovative research opportunities on the evolution of socio-ecosystems and landscapes.

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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