Soil Systems

Biodegradation is emerging as a promising and sustainable strategy for the removal of polycyclic aromatic hydrocarbons (PAHs) from soil. This approach integrates various strategies, such as bioaugmentation and biostimulation of microbial communities with tolerance and biodegradation capabilities. This study evaluated the biodegradation potential of the fungal isolate Trichoderma harzianum (strain UPS-Y1) in mesocosms of soil contaminated with polycyclic aromatic hydrocarbons present in bunker diesel fuel, which is widely used in thermoelectric power plants. The experimental monitoring was conducted by quantifying these compounds at 30, 60, and 90 days, with three replicates for both the inoculated treatments and the non-inoculated controls at each sampling time. The controls were subjected to the same biostimulation and management conditions but without Trichoderma harzianum inoculation. Statistical analyses, including the Friedman test and multivariate techniques, showed temporal changes in PAH concentrations and differences between the inoculated and non-inoculated mesocosms. At 60 days, the concentrations of several compounds, such as naphthalene, acenaphthene, fluorene, fluoranthene, benzo[a]pyrene, benzo[g,h,i]perylene, and indene, decreased to levels below the analytical detection limit. Following this pattern, at the end of 90 days, 14 of the analyzed compounds showed concentrations below the analytical detection limit. These findings indicate that T. harzianum bioaugmentation was associated with enhanced PAH reduction under the biostimulation conditions applied in this study. However, because abiotic controls were not included, the observed reductions cannot be attributed exclusively to fungal activity.

Corporate carbon offsetting schemes heavily rely on tree planting for carbon sequestration, and in Scotland, the government presents tree planting as a key carbon sink in the face of climate change. However, carbon offsetting schemes rarely consider associated fluxes in soil organic carbon (SOC) driven by afforestation. Soils in woodlands store approximately 75% of the total ecosystem carbon, yet planting trees on existing carbon-rich soils or grassland may result in changes in soil carbon that take decades for tree biomass to recover. This study provides a methodological framework using the chronosequence approach (space-for-time substitution) to measure whole-ecosystem carbon storage for existing commercial carbon sequestration schemes. A proof-of-concept pilot study was carried out at the University of Edinburgh’s Rullion Green site, gathering 35 soil samples across unplanted baselines, a recent 2025 planting scheme, and a mature mixed woodland. The findings of this proof-of-concept study show that soil carbon in the newly planted area (5.06% SOC) was lower than in the mature woodland (7.64% SOC) and was significantly lower (p = 0.026) than the unplanted baseline (7.11–8.65% SOC depending on slope). The carbon in the recently planted trees (5.00 t C/ha) did not offset the carbon losses from soil, with a drop in ecosystem carbon of 155.51 t C/ha compared to all baseline samples, 97.98 t C/ha when compared to baseline samples at the same topographic elevation, and 418.23 t C/ha compared to the mature woodland. Previous studies have found that deep soil carbon losses may be deeper than topsoil losses, so this may be an underestimate of carbon losses following planting, requiring further study. The methodology and trial study suggest that initial tree planting may not guarantee an immediate net increase in ecosystem carbon until trees become mature. The methodology therefore provides a tool to help mitigate greenwashing in the offsetting industry. The methodology will now be applied in further research to other sites across northern England to determine what the impact of tree planting for carbon sequestration is on soil in the UK.

As drainage-impeded soils cover extensive acreage that is widely used as grazed pastures, understanding how they retain organic matter and potentially mineralizable N may be important for improving management. We evaluated the vertical distribution of potentially mineralizable N (PMN), carbon, and phosphorus (M1P) in pastures with well-drained (WD) and drainage-impeded (Dimp) soil under broiler litter (BL) and mineral (Min) fertilization legacies. The study was conducted on ten 0.8 ha pastures in Eatonton, Georgia. In BL pastures, WD soils had greater PMN (40–90 cm) and LOI (0–90 cm) but lower M1P (20–90 cm) compared to Dimp. In Min pastures, WD soils had greater PMN (0–40 cm) and LOI (0–90 cm) but lower M1P (5–10 and 40–90 cm) compared to Dimp. These results suggest carbon loss in Dimp soils, probably occurring due to wetting and drying cycles. The results also suggest more P downward movement in Dimp than in WD soils. Stepwise regression identified the most significant variables related to PMN; M1P accounted for most of the variability in Min WD, LOI accounted for the most variability in Min Dimp, and BL WD, and pH accounted for most variability in BL Dimp across all depths. Our findings indicate that drainage-impeded (moderately well-drained and somewhat poorly drained) pasture soils retain C and mineralize N differently than well-drained soils.