From Litterfall to Respiration: Investigating Soil Processes in Differing Irish Forests

Forest ecosystems are critical hubs of biogeochemical activity, playing a major role in global carbon cycling by storing and cycling substantial quantities of terrestrial carbon both above and below ground. The forest floor serves as a dynamic interface where organic inputs, such as litterfall and root turnover, drive soil processes that influence carbon fluxes. Understanding the interactions between photosynthetic activity, soil respiration, and decomposition is key to determining whether forests act as carbon sources or sinks. To gain deeper insights into these processes, it is essential to measure soil respiration and partition its autotrophic and heterotrophic components, linking aboveground organic inputs to belowground carbon and nutrient cycling.

This study investigates soil carbon flux dynamics in three distinct Irish forest types: a commercial coniferous forest on mineral soil, a broadleaf-dominated native woodland on mineral soil, and a mixed-species forest on peat soil. These forests, characterized by differences in soil type, species composition, and management practices, offer unique insights into the interactions between litterfall, fine root dynamics, and soil respiration.

Aboveground litter inputs were quantified through monthly litterfall collection using bucket traps over a two-year period, revealing distinct patterns both within and between sites. Litter decomposition was assessed with one-year litterbag experiments, while fine root production and turnover were evaluated using one-year in-growth core experiments. Soil respiration was measured twice monthly over a two-year period using two trenched collars installed to a depth of 25 cm and two untrenched collars, with the inclusion and removal of litter enabling a detailed analysis of autotrophic and heterotrophic contributions. Elemental analysis of mineral soils (0–50 cm) and organic soils (0–150 cm) provided key insights into carbon, hydrogen, and nitrogen content, offering valuable data on soil organic matter composition and nutrient availability across the soil profile in the three forest types.

Over the two-year study period, results show that the commercial coniferous forest exhibited the lowest average total soil respiration rates, averaging 52.10 tonnes CO₂/ha/yr. Conversely, the native woodland and the mixed-species peatland forest showed similar and higher soil respiration rates, averaging 54.31 tonnes CO₂/ha/yr. Across all sites and seasons, heterotrophic respiration contributed more to total ecosystem respiration than autotrophic respiration.

By integrating data on litterfall, decomposition, fine root dynamics, and soil elemental composition, this study highlights the critical role of organic inputs and root processes in driving soil respiration and carbon cycling in forests. These findings will enhance carbon modeling efforts, improve predictions of ecosystem responses to environmental change, and inform sustainable forest management strategies for climate change mitigation.