The effect of ectomycorrhizal fungal exposure on nursery-raised Pinus sylvestris seedlings: plant transpiration under short-term drought, root morphology and plant biomass.

Drought is a major environmental stressor that limits seedling growth. Several studies have found that some ectomycorrhizal fungi may increase the drought tolerance of nursery-raised seedlings. However, the precise role that different ectomycorrhizal fungi species play in drought tolerance remains unclear. We evaluated the transpiration rate of Pinus sylvestris seedlings under drought stress in greenhouse conditions by exposing seedlings to 10 ectomycorrhizal fungi species, with different functional traits (exploration type and hydrophobicity), and to 3 natural soil inoculums. We measured the transpiration and water potential of the seedlings during a 10-day drought period and a 14-day recovery period. We then analyzed their root morphology, stem, needle, root biomass and needle chlorophyll fluorescence. We showed that exposing seedlings to ectomycorrhizal fungi or soil inoculum had a positive effect on their transpiration rate during the driest period and through the recovery phase, leading to 2- to 3-fold higher transpiration rates compared with the nonexposed control seedlings. Seedlings exposed to medium-distance ectomycorrhizal fungi performed better than other exploration types under drought conditions, but ectomycorrhizal fungi hydrophobicity did not seem to affect the seedlings response to drought. No significant differences were observed in biomass accumulation and root morphology between the seedlings exposed to different ectomycorrhizal fungi species and the control. Our results highlight the positive and species-specific effect of ectomycorrhizal fungi exposure on drought tolerance in nursery-raised Scots pine seedlings. The studied ectomycorrhizal fungi functional traits may not be sufficient to predict the seedling response to drought stress, thus physiological studies across multiple species are needed to draw the correct conclusion. Our findings have potential practical implications for enhancing seedling drought tolerance in nursery plant production.

Enhancing boreal forest resilience: A four-year impact of biochar on soil quality and fungal communities.

Boreal forests commonly suffer from nutrient deficiency due to restricted biological activity and decomposition. Biochar has been used as a promising strategy to improve soil quality, yet its impacts on forest soil microbes, particularly in cold environment, remains poorly understood. In this study, we investigated the effects of biochar, produced at different pyrolysis temperatures (500 °C and 650 °C) and applied at different amounts (0.5 kg·m-2 and 1.0 kg·m-2), on soil property, soil enzyme activity, and fungal community dynamics in a boreal forest over a span of two to four years. Our results showed that, four-year post-application of biochar produced at 650 °C and applied at 1.0 kg·m-2, significantly increased the relative abundance of Mortierellomycota and enhanced fungal species richness, α-diversity and evenness compared to the control (CK) (P < 0.05). Notably, the abundance of Phialocephala fortinii increased with the application of biochar produced at 500 °C and applied at 0.5 kg·m-2, exhibiting a positively correlation with the carbon cycling-related enzyme ß-cellobiosidase. Functionally, distinct fungal gene structures were formed between different biochar pyrolysis temperatures, and between application amounts in four-year post-biochar application (P < 0.05). Additionally, correlation analyses revealed the significance of the duration post-biochar application on the soil properties, soil extracellular enzymes, soil fungal dominant phyla, fungal community and gene structures (P < 0.01). The interaction between biochar pyrolysis temperature and application amount significantly influenced fungal α-diversity (P < 0.01). Overall, these findings provide theoretical insights and practical application for biochar as soil amendment in boreal forest ecosystems.

High organic carbon content constricts the potential for stable organic carbon accrual in mineral agricultural soils in Finland.

Sequestering carbon into agricultural soils is considered as a means of mitigating climate change. We used agronomic soil test results representing c. 95% of the farmed land area in Finland to estimate the potential of the uppermost 15 cm soil layer of mineral agricultural soils to sequester organic carbon (OC) and to contribute to the mitigation of climate change. The estimation of the maximum capacity of mineral matter to protect OC in stable mineral-associated form was based on the theory that clay and fine-sized (fines = clay + silt) particles have a limited capacity to protect OC. In addition, we used the clay/OC and fines/OC ratios to identify areas with a risk of erosion and reduced productivity, thus indicating priority areas potentially benefitting from the increased soil OC contents. We found that 32-40% of the mineral agricultural soils in Finland have the potential to further accumulate mineral-associated OC (MOC), while in the majority of soils, the current OC stock in the uppermost 15 cm exceeded the capacity of mineral matter to protect OC. The nationwide soil OC sequestration potential of the uppermost 15 cm in mineral agricultural soils ranged between 0.21 and 0.26 Tg, which corresponds to less than 2% of annual greenhouse gas emissions in Finland. The fields with the highest potential for SOC accrual were found in the southern and southwestern parts of the country, including some of the most intensively cultivated high-clay soils. Although the nationwide potential for additional OC sequestration was estimated to be relatively small, the current OC storage in Finnish arable mineral soils (0-15 cm) is large, 128 Tg. Farming practices enabling maximum OC input into the soil play an important role as a tool for mitigating the loss of carbon from high-OC soils in the changing climate. Furthermore, especially in high-clay areas with potential for MOC accrual, efforts to increase soil OC could help improve soil structural stability and therefore reduce erosion and the loss of nutrients to the aquatic environments.