Mountain grasslands as carbon sinks and energy hubs: a study of Western Carpathians in Slovakia

Mountain grasslands are unique ecosystems that provide many ecosystems' services. They are an important carbon pool and can also act as a source of bioenergy. The study focused on 4 grassland types (Lowland hay meadows, Mountain hay meadows, Wet grassland of sub-montane zones and Artificial grasslands) and 4 soil types (Fluvisols, Cambisols, Leptosols, Stagnosols) in 5 mountain ranges (Great Fatra Mts., Low Tatra Mts., Slovak Paradise Mts., Čergov Mts., Slánske Hills Mts.) of the Western Carpathians in Slovakia. The results showed that of the total carbon stock of the mountain ecosystems equal to 2.120 × 10³ tons, 94% was stored in soil. The total carbon density followed this pattern: Fluvisols (100.64 ± 7.87 t/ha) > Stagnosols (84.17 ± 7.90 t/ha) > Leptosols (56.34 ± 6.20 t/ha) > Cambisols (55.43 ± 5.09 t/ha). Soil organic carbon density was also significantly affected by elevation, with the highest values between 600 and 900 m asl. (70.46 ± 4.23 t/ha). Grassland type significantly affected carbon density in living plant biomass, where Mountain hay meadows showed the significantly lowest values (P < 0.05) for carbon density in above-ground biomass (0.79 ± 0.05 t/ha) and below-ground biomass (2.24 ± 0.16 t/ha). The hierarchical clustering dendrogram revealed that the soils from the Low Tatra Mts. differed significantly from those of other mountain ranges and were characterized by high pH, very high soil organic carbon content, high levels of plant-available magnesium, and high C: N ratio in the soil. The calculated biomethane production ranged from 6,606 GJ in the Slovak Paradise Mts. for Lowland hay meadows, to 122,888 GJ in the Low Tatra Mts., which had the largest area of grassland habitats. The total theoretical energetic potential of biomethane production from all evaluated grassland habitats exceeded 1,139 GJ. The energetic potential values followed the following order: Slovak Paradise Mts. < Čergov Mts. < Slánske Hills Mts. < Great Fatra Mts. < Low Tatra Mts.