Forests contribute strongly to global carbon (C) sequestration and the exchange of greenhouse gases (GHG) between the soil and the atmosphere. Whilst the microbial activity of forest soils is a major determinant of net GHG exchange, this may be modified by the presence of litter through a range of mechanisms. Litter may act as a physical barrier modifying gas exchange, water movement/retention and temperature/irradiance fluctuations; provide a source of nutrients for microbes; enhance any priming effects, and facilitate macro-aggregate formation. Moreover, any effects are influenced by litter quality and regulated by tree species, climatic conditions (rainfall, temperature), and forest management (clear-cutting, fertilization, extensive deforestation). Based on climate change projections, the importance of the litter layer is likely to increase due to an litter increase and changes in quality. Future studies will therefore have to take into account the effects of litter on soil CO2 and CH4 fluxes for various types of forests globally, including the impact of climate change, insect infestation, and shifts in tree species composition, as well as a better understanding of its role in monoterpene production, which requires the integration of microbiological studies conducted on soils in different climatic zones.

Understanding the functioning of different forest ecosystems is important due to their key role in strategies for climate change mitigation, especially through soil C sequestration. In controlled laboratory conditions, we conducted a preliminary study on six different forest soils (two coniferous, two deciduous, and two mixed sites comprising trees of different ages) collected from the same region. The aim was to explore any differences and assess seasonal changes in soil microbial parameters (basal respiration BR, microbial biomass Cmic, metabolic quotient qCO2, dehydrogenase activity DHA, and Cmic:Corg ratio). Indicator- and forest-specific seasonality was assessed. In addition to litter input, soil parameters (pH, nutrient content, texture and moisture) strongly regulated the analyzed microbial indicators. PCA analysis indicated similarity between mature mixed and deciduous forests. Among annual mean values, high Cmic and DHA with simultaneously low qCO2 suggest that the mature deciduous stand was the most sustainable in microbial activities among the investigated forest soils. Research on the interrelationship between soil parameters and forest types with different tree ages needs to be continued and extended to analyze a greater number of forest and soil types.

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<p>Soils may act as a biological sink for methane (CH<sub>4</sub>) through methanotrophic activity. This process is particularly important in the farming sector, as CH<sub>4</sub> emissions from livestock and manure storage often dominate the greenhouse gas (GHG) budget. This places a particular emphasis on the identification of management practices that may increase the capacity of soils to absorb CH<sub>4</sub>. In this study we examined  practices with the potential to improve the CH<sub>4</sub> balance at farm level, including the effect of biochar as a soil additive, and the potential of silvopasture systems. Experiments conducted under controlled laboratory conditions revealed that the addition of biochar increased the rate of CH<sub>4 </sub>oxidation in the mineral and manure-fertilized silty soil, although such effect has not been confirmed in all soil types. Using biochar produced from crop by products  may also provide a way of managing agricultural wastes with concomitant practical benefits. Silvopastoral systems can also alter the CH<sub>4</sub> balance of farms because of the effect of the presence of trees on microclimate and soil conditions. However, relatively few studies have assessed the potential of trees to improve CH<sub>4</sub> budgets at the farm level in Mediterranean silvopastoral systems. In-situ measurements of soil-atmosphere CH<sub>4</sub> fluxes were undertaken to evaluate the CH<sub>4</sub> uptake potential of pastures below and beyond tree canopies. Preliminary results showed CH<sub>4</sub> emissions in open tree-less pastures, but not under trees, which showed mainly CH<sub>4</sub> uptake. This result highlights the potential of silvopastoral systems to improve the CH<sub>4</sub> balance at farm level perhaps in combination with biochar additions. Nevertheless, the mitigation potential of different soil additives and silvopastoral  practices at farm level are still a subject of research in need of further studies.</p><p>This work was funded by the National Centre for Research and Development within GHG Manage (ERA-GAS/I/GHG-MANAGE/01/2018) and ReLive (CIRCULARITY/61/ReLive/2022); Joint Call of the Co-fund ERA-Nets Programme, SusCrop (Grant N° 771134), FACCE ERA-GAS (Grant N° 696356), ICT-AGRI-FOOD (Grant N° 862665) and SusAn (Grant N° 696231), Spanish Ministry of Science and Education (PCI2021-122100-2A).</p>