Cascading effects of canopy mortality drive long-term changes in understorey diversity in temperate old-growth forests of Europe

Questions: We investigated the influence of protracted mortality of a dominant canopy tree (Abies alba) on long-term understorey dynamics. We ask (a) how tree regeneration and understorey species diversity and composition changed over 32 years; and (b) whether the observed changes were mainly driven by mortality of A. alba. Location: Three old-growth forest reserves dominated by A. alba and Fagus sylvatica in the Dinaric Mountains of Slovenia. Method: Tree layer and understorey regeneration and herbs were surveyed in 147 plots across the three forest reserves in 1983 and 2015. Soils were also sampled in 2015. The study period coincides with a protracted period of increased A. alba mortality in the canopy layer associated with anthropogenic emissions. Results: Between 1983 and 2015, the decline in canopy layer A. alba caused a recruitment pulse of F. sylvatica regeneration to the subcanopy tree layer across the three reserves. These changes were accompanied by a significant decline in plot level herb species richness. A model-based analysis of beta-diversity revealed significant community convergence during the study period, mainly caused by the loss of rare species. Ellenberg values indicate that these changes were mainly driven by loss of understorey light, while an increase in soil pH may have played a role also. Conclusions: This observational study suggests that the long-term decline of A. alba resulted in a cascade of processes - widespread F. sylvatica recruitment that impeded penetration of light to the forest floor, and possibly a change in soil conditions due to the decline of coniferous litter. These changes caused a significant loss of herb diversity and homogenization of the understorey community across the three sites. This study sheds light on the potential cascading consequences triggered by episodes of increased tree mortality resulting from global-change-type drivers

Consequences of minimum soil tillage on abiotic soil properties and composition of microbial communities in a shallow Cambisol originated from fluvioglacial deposits.

A long-term field experiment was run for 12 years to evaluate the impact of minimum tillage (MT) compared to conventional mouldboard ploughing (CT) on soil chemical, physical and microbial properties in a shallow Cambisol formed over fluvioglacial deposits of Drava river in Slovenia. Significant differences between MT and CT were found in vertical distribution of soil organic C (SOC) and nutrients (total N and plant available potassium); under MT, concentrations decreased from the soil surface to the lower layers, as opposed to CT which maintained rather uniform distribution down to the ploughing depth. MT in comparison with CT also increased the proportion of water-stable 2–4-mm-sized aggregates (80.9 and 61.3 %, respectively), water holding capacity (24.8 and 22.2 %, respectively) and plant available water (13.4 and 10.3 %, respectively) in the upper 0–10-cm soil layer. Bulk density, porosity, the proportion of water-stable 1–2-mm-sized aggregates and infiltration rate showed no significant differences between the tillage treatments. SOC content in the upper 0–10-cm soil layer was not significantly different between MT and CT (1.60 ± 0.07 and 1.45 ± 0.05 %, respectively), as well as the overall stock in the investigated soil profile (0–60 cm) remained unaffected (57.4 ± 0.8 and 59.1 ± 2.2 t ha−1, respectively). Microbial biomass, estimated by the total soil DNA, was higher in MT than CT in the 0–10-cm layer. Furthermore, a positive linear dependence of microbial biomass on SOC content was observed. Fingerprinting of bacterial, fungal and archaeal communities indicated that microbial community composition changed by long-term MT, whereas changes in microbial diversity were not detected for any domain. The most pronounced shifts in the composition were found for bacterial communities in the 10–20-cm layer, while the composition of fungal communities slightly changed in the upper 0–10 cm of MT soil. The composition of archaeal communities was not affected by the tillage or by the soil depth. Our results indicate that MT generates modest changes in soil structure and soil water retention properties and could support measures against erosion, drought and nutrient leaching. Considering increased microbial biomass in the topsoil of MT and shifts in microbial diversity, the impacts of MT on soil microbiome are also evident and need to be further investigated to identify the affected functional traits

Resilience of bacteria, archaea, fungi and N-cycling microbial guilds under plough and conservation tillage, to agricultural drought

Climate change causes droughts, which in turn cause significant physiological stress for soil microorganisms. In this study, we investigated how the abundance of total bacterial, crenarchaeal and fungal communities and the abundance of N-cycling microbial guilds responded to a severe agricultural drought event in a long-term experiment of minimum tillage (MT) and conventional ploughing (CT) at two soil depths. This study was financially supported by the European Commission within the EcoFINDERS project (FP7-264465), CORE Organic Plus funding bodies within the FertilCrop project, and by the Slovenian Research Agency within the programme P4-0085

Mercury in urban soils: a comparison of local spatial variability in six European cities

The objective of this study was to quantify and assess for the first time the variability of total mercury in urban soils at a previous termEuropeannext term level, using a systematic sampling strategy and a common methodology. We report results from a comparison between soil samples from Aveiro (Portugal), Glasgow (Scotland), Ljubljana (Slovenia), Sevilla (Spain), Torino (Italy) and Uppsala (Sweden). At least 25 sampling points (in about 4-5 ha) from a park in each previous termcitynext term were sampled at two depths (0-10 and 10-20 cm). Total mercury was determined by pyrolysis atomic absorption spectrometry with gold amalgamation. The quality of results was monitored using certified reference materials (BCR 142R and BCR 141R). Measured total mercury contents varied from 0.015 to 6.3 mg kg− 1. The lowest median values were found in Aveiro, for both surface (0-10 cm) and sub-surface (10-20 cm) samples (0.055 and 0.054 mg kg− 1, respectively). The highest median mercury contents in soil samples were found in samples from Glasgow (1.2 and 1.3 mg kg− 1, for surface and sub-surface samples, respectively). High variability of mercury concentrations was observed, both within each park and between previous termcities.next term This variability reflecting contributions from natural background, previous anthropogenic activities and differences in the ages of previous termcitiesnext term and land use, local environmental conditions as well as the influence of their location within the urban area. Short-range variability of mercury concentrations was found to be up to an order of magnitude over the distance of only a few 10 m