Interactions between deciduous and coniferous litter in decomposition processes: Insights from ATR-FTIR spectroscopy and elemental analyses

Abstract

Forest litter decomposition is crucial for carbon and nutrient cycling, especially in mixed broadleaf-coniferous forests. Interactions between different litter types can accelerate or inhibit decomposition, depending on spe- cies composition, microbial activity, and environmental factors. This study examines how litter samples from oak (Quercus sp.), beech (Fagus sylvatica L.), and pine (Pinus sylvestris L.) decomposes in pure and mixed stands across four European sites. Samples were collected at different decomposition stages (L, F, and H layers) and analysed for total organic carbon, total nitrogen, total phosphorus, and molecular composition using ATR-FTIR spec- troscopy. A generalized linear mixed model assessed the influence of species identity, forest type, and pine proportion in mixed stands on decomposition and nutrient dynamics. Our results revealed contrasting effects of litter mixing. Broadleaf litter enhanced pine needle decomposition, particularly in the H layer, likely due to facilitation. Conversely, broadleaf litter decomposition, specially oak in the F layer, was inhibited in mixed stands. Beech litter degradation remained largely unaffected. ATR-FTIR analysis suggested molecular trans- formations, with increased aromatic compounds and reduced aliphatic groups, especially in mixed stands, though these spectral interpretations carry some uncertainty. These findings highlight the role of species composition in shaping litter decomposition dynamics. While ATR-FTIR provided useful information on chemical changes during decomposition, its interpretation should be complemented with other approaches to improve confidence in functional inferences. Incorporating species-specific responses can inform forest management strategies aiming to balance nutrient cycling and long-term carbon sequestration.