Seasonal dynamics of the bacterial community in forest soils under different quantities of leaf litter

Abstract : Soil microbial communities play an important role in soil carbon functioning, particularly in forest ecosystems. Their variation in response to climate change may affect soil carbon processes, highlighting the importance of understanding how environmental factors affect microbial communities. This study aimed to determine to what extent an increase in the quantity of fresh litter may affect heterotrophic mineralization of organic carbon and bacterial community structure in soil and litter. A litter manipulation experiment was performed in situ in a temperate deciduous forest. Three treatments of fresh litter inputs were considered: litter exclusion, natural conditions (control) and litter addition (twice the natural rate). Microbial and functional ecological approaches were combined to consider bacterial community structure in soil and litter using a molecular fingerprinting technique, and measurement of soil respiration both in terms of efflux intensity and isotopic composition of respired CO2 (natural abundance) over one year. The quantity of fresh litter seemed to affect soil and litter bacterial community structure and to interact with soil temperature and moisture to determine the temporal variation in the bacterial community on a month to season scale. In addition, this study highlighted the large temporal variability in soil and litter bacterial community structure and that this variability may affect our ability to relate bacterial community structure to respiration processes. This highlights the need for an intensive characterisation of the bacterial community structure to relate its variations to variations in soil respiration processes.