Seasonal changes in anecic earthworm cast properties reflect food source variability in Northern Vietnam /Bottinelli, Nicolas Doan, T. T. Dang, X. Benedetti, M. F. /Jouquet, Pascal Tran, T. M. Rumpel, C. Bioturbation Anecic Organic matter transformation Tropical soil The objective of this study was to assess seasonal variability of anecic earthworm cast properties in contrasting tropical ecosystems as it might provide information on the earthworms' feeding behavior during different times of the year. Fresh casts deposited at the soil surface by the anecic earthworm Amynthas adexilis and topsoil aggregates without trace of earthworm activity were collected at five dates across one year in meadow and woodland in northern Vietnam. We analysed elemental composition, stable isotopes, lignin signatures and rare earth elements (REEs) to investigate the changes in organic matter (OM) and mineral composition. Casts were consistently enriched in less degraded OM compared to topsoil aggregates, but their OM composition varied markedly throughout the year, with strong contrasts between habitats. In meadow, cast C content, C/N and lignin content fluctuated by 31, 23 and 65%, and their seasonal trajectories closely mirrored those of adjacent topsoil aggregates. In woodland, seasonal changes were much more pronounced and decoupled from those of the topsoil aggregates. Indeed, lignin content varied more than 14-fold, and isotopic signatures showed clear temporal shifts, indicating major seasonal changes in the OM type ingested by A. adexilis. In contrast, REE patterns remained stable across sampling dates in both ecosystems, suggesting that temporal changes in cast properties were primarily driven by food source variability rather than changes in feeding depth. In meadow, single-date estimates of C incorporated into casts ranged from 7.6 to 10.0 t C center dot ha(-1)center dot yr(-1), whereas in woodland variability was much lower (1.3 to 1.5 t C center dot ha(-1)center dot yr(-1)). We conclude that A. adexilis feeds mainly on topsoil. However, as OM composition of food sources may change with time, it is necessary to make multiple seasonal measurements of cast composition in some ecosystems to capture the full variability of earthworm effects on SOM dynamics under tropical condition. Moreover, ecosystem management should account for seasonal variability in earthworm activity, as it may directly affect soil carbon and nutrient dynamics. 2026 text https://www.documentation.ird.fr/hor/fdi:010097330 fdi:010097330 Bottinelli Nicolas, Doan T. T., Dang X., Benedetti M. F., Jouquet Pascal, Tran T. M., Rumpel C.. Seasonal changes in anecic earthworm cast properties reflect food source variability in Northern Vietnam. 2026, 223, 107098 [10 p.] EN VIET NAM ZONE TROPICALE