Variability in litter inputs affecting soil fungi and bacteria through moisture and carbon content in forest soil

Soil organic matter content is a main driver of soil functions and ecosystem services. Various quantity of litter inputs was studied in a Quercetum-petraeae-cerris forest in northeastern Hungary at the Sikfokut DIRT (Detritus Input and Removal Treatment) experimental site. The goal of the project was to assess how rates and sources of plant litter inputs might control the accumulation and dynamics of organic matter and nutrients in forest soils over decadal time scales. Six treatments were applied at the experimental site. Beside the control (CO) condition, two detritus addition (double litter (DL) and double wood (DW)) and three detritus removal (no litter (NL), no roots (NR) and no input (NI) treatments were applied in which detritus quantities were manipulated above and below ground. Our aim was the study of the relationship between the litter treatments, their carbon (C) content and the number of microorganisms and biomass of fungi. Litter treatments also had a significant effect on soil microorganisms and soil organic carbon (SOC) content. These effects decreased in parallel with soil depth. Fungal biomass values were more than five times higher for DL (2 mg fungi g(-1) soil) than for the soils of NI (0.4 mg fungi g(-1) soil) condition in the upper 5 cm layer, while 0.57 (DL) and 0.08 (NI) values were measured in the 15-25 cm layer. The most probable number (MPN) method, which measures the number of certain groups of living and active microorganisms (fungi and bacteria), showed even greater differences between the treatments. Positive direct and indirect effects of greater organic matter inputs is affected the soil functioning through on better moisture and C content in soils. Litter entering the forest floor resulted in a larger amount of organic substrate and inorganic nutrients. In addition, it resulted in more favorable microclimatic conditions (lower temperature and soil moisture fluctuation) in the soils, which increased the number of microorganisms and the biomass of fungi. There is no significant difference in the number of microbes between the control and doubling treatments (DL, DW). Furthermore, in the case of fungal biomass, there is a significant difference only in the upper 5 cm layer of the DL. These results explain the significantly higher SOC content of the DL treatment compared to the other treatments, suggesting a weaker priming effect. In summary, the results of our research suggest that litter removal had a much greater effect on soil microbial number and fungal biomass as well as SOC content than the addition of a similar amount of litter.