This study was carried out in alien warmth-tolerant forest plantations of red oak (Quercus rubra), common beech (Fagus sylvatica) and European larch (Larix decidua). We compared the changes in foliar litterfall mass and biochemical composition after five months of cold period. The mean mass of fresh foliar litterfall collected in late autumn was 30% higher in red oak compared to the larch and beech plantations. After the cold period, the reduction of foliar litterfall mass did not exceed 10% in any of the studied plantations. The fresh foliar litterfall of red oak was the richest in cellular fibre and easily decomposable glucose and nutrients such as P and Mg, larch was distinguished by the highest lignin, N, K and Ca concentrations, while beech fresh foliar litterfall was the poorest in the aforementioned nutrients. After the cold period, the changes in the biochemical composition of foliar litterfall revealed different patterns. In the spring, the beech and red oak foliar litterfall was the richest in N, P and Ca, meanwhile the larch foliar litterfall still had the highest concentration of lignin but, in contrast to the autumn, was the poorest in nutrients. After the cold period Lignin: N, C: N and C: P ratios reached critical values indicating that the foliar litterfall of beech and red oak had started to decompose. The highest lignin concentration and the highest and most stable Lignin: N, C: N, C: P and N: P ratios after the cold period indicated that the slowest foliar litterfall decomposition took place in the larch plantation.

Organic soils are one of the largest natural terrestrial carbon stores, especially in boreal, temperate, and tropical wet climates. In these environments, scarcity of oxygen due to soil wetness has enabled the accumulation of organic carbon deposits over the past millennia. In Europe, organic soils account for only 3% of total agricultural land. Yet, they play a significant role in meeting Europe's 2030 and 2050 climate change mitigation targets. However, drainage of these soils, as a common management practice aiming for higher agricultural productivity, transforms these carbon-rich soils into a significant GHG source.Water-level management practices are critical in agriculture to minimize soil degradation and nutrient leaching. Fluctuations in water levels may alter soil physical and chemical conditions and potentially cause GHG emissions. Deep draining leads to an increase in carbon dioxide (CO2) and nitrous oxide (N2O) emissions due to increased soil mineralization. On the other hand, methane (CH4) emissions are lower compared to natural wetlands where soil drainage and tillage do not occur. Land use, climate zone, soil nutrient status, fertilization, and drainage status are closely related to estimating GHG budgets from managed sites on organic soils.Available data on actual GHG emissions from drained and nutrient-rich organic soils under different management practices show considerable variation. Therefore our study's main objectives are: (I) to update GHG emission factors for organic soils in drained croplands and grasslands and (ii) to calculate soil carbon and nitrogen budgets applicable to the Baltic countries. A two-year study was conducted from January 2021 to December 2022 to assess the impact of drainage and land use on GHG fluxes in the Baltic countries.Fluxes in croplands and perennial grassland on nutrient-rich organic soils with different drainage conditions were determined by groups: (I) excessively drained croplands, (II) excessively drained grasslands, (III) moderately drained grasslands, (IV) rewetted grasslands, and (V) non-managed fens as reference sites. Measurements were done monthly (Latvia and Lithuania) or twice per month (Estonia) using the manual static dark chamber method (N2O, CH4), the dynamic transparent chamber method for net ecosystem exchange, and the dynamic dark chamber for soil heterotrophic respiration (CO2). In addition, we measured associated environmental parameters (water table level, soil moisture and temperature, and solar radiation). For biomass analyses, we took samples once in the measurement period.Our preliminary results show that all grasslands were annual CH4 sinks, while fens soils in natural status were a source of CH4. All studied sites were N2O sources on an annual basis, and croplands were the strongest emitters, as was expected. Higher N2O emissions and temporal variability were associated with sites characterized by high groundwater levels with high seasonal fluctuations. Soil heterotrophic respiration fluxes peaked over all the study sites during the summer. As the last field campaign shortly ended, more detailed data analyses will be presented at the conference.This research was supported by the LIFE programme project "Demonstration of climate change mitigation potential of nutrients rich organic soils in Baltic States and Finland", (2019-2023, LIFE OrgBalt, LIFE18 274CCM/LV/001158).