Litter nutrient turnover influences soil CO2 emissions in oak-dominated ecosystems

Global biochemical cycles in forest ecosystems may shift as a result of climate change conditions. It is essential to comprehend how biogeochemical cycles and environmental factors control nutrient releases and storage in soils and forest ecosystems. Moreover, soil is the largest storage pool of carbon and nutrients. Nutrient availability, particularly in litter and soil, directly influences tree growth and biomass accumulation, which in turn impacts forest structure, productivity, nutrient cycling, and soil CO₂ emissions.

In this work, we investigate how the litter nutrient dynamics and turnover can influence the soil CO₂ emissions in Mediterranean oak-dominated ecosystems with a soil manipulation experiment in the Xanthi region of northern Greece. We studied soil CO₂ efflux under three organic matter input treatments: Control [CON] (undisturbed), No-Litter [NL] (aboveground litter excluded) and No-Litter-No-Roots [NLNR] (both litter and roots excluded). Monitoring plots were established in a broadleaf evergreen ecosystem dominated by Quercus coccifera L. and Phillyrea latifolia L. Equal plots were established in a deciduous oak forest dominated by Quercus frainetto Ten., followed by Quercus cerris L. and Quercus petraea (Matt.). Using a Li-8100 automated soil CO₂ efflux system, soil respiration, moisture and temperature measurements were conducted at 54 points in total, once every three months for two years (2023-2024). We also analyzed a range of nutrients in litterfall and forest floor and estimated their turnover rates to determine their effect on soil respiration. Our results showed that in both ecosystems, soil temperature and moisture predominantly controlled soil CO₂ effluxes. Litter turnover was identified as a key driver of soil CO₂ efflux in broadleaf evergreens linked to the nutrient dynamics of carbon (C), nitrogen (N), manganese (Mn), and calcium (Ca). Similarly, in deciduous oaks, litter turnover significantly influenced soil CO₂ efflux, particularly in relation to C, N, C/N, and potassium (K). This work supports our better understanding of the influence of nutrient cycling on soil emissions in Mediterranean forest ecosystems.