Soil carbon turnover of drained and naturally wet mineral forest soils in Latvia

Assessment of changes in carbon (C) stocks in mineral soils typically relies on the steady-state C stock values, which are influenced by various long-term land-use and management scenarios. This conventional approach limits understanding of the short-term soil C balance, including in lands not subject to land-use or management changes. Additionally, the role of the soil moisture condition impact on the mineral soil C balance is not broadly studied. To enhance our understanding of the effects of the soil moisture on C balances of mineral soils, this research conducted soil CO2 emission monitoring in forests with both drained and naturally wet mineral soils. The study was implemented across 18 forest sites with dominant species of aspen (Populus tremula L), birch (Betula pendula Roth, Betula pubescens Ehrh.), black alder (Alnus glutinosa (L.) Gärtner) and Scots pine (Pinus sylvestris L.). Emission monitoring was performed using the closed static opaque chamber method. Concurrent measurements of the soil temperature and the groundwater level depth were also conducted. Our research revealed that CO2 emissions resulting from soil respiration in both naturally wet and drained soils showed no notable differences, indicating that the mineral soil moisture regime has a minimal impact on C outflows from these soils. This finding implies that the C balance in mineral soils is largely dictated by the influx of C from vegetation residues and litter. Thus, for the conservation or enhancement of C stocks in mineral soils, maintaining the soil moisture regime that optimizes the decomposition and accumulation of vegetation litter is essential.