A bizarre layer cake: Why soil animals recolonizing polluted areas shape atypical humus forms

During soil recolonization by macrofauna in areas previously defaunated by industrial pollution, non-typical humus forms are produced. Given that the evidence of zoogenic activity cessation with increased forest litter depth in these humus forms, we tested the hypothesis that the lower organic layers are more toxic than the upper ones. The studies were conducted in the southern taiga, near the Middle Ural Copper Smelter (Revda city, Russia), in spruce-fir and birch forests. We investigated the series of degraded humus forms at different recovery stages, including those without signs of regradation, as well as at the initial and advanced recovery stages. In the organic layers, each of which were 1-2 cm thick and 6-8 cm in total, we measured the following parameters: pH(water), total acidity, the content of exchangeable Ca2+ and Mg2+, acid-soluble and exchangeable metals (Cu, Pb, Fe, Cd, and Zn), organic carbon, and total nitrogen. Simultaneously, we diagnosed the degree of zoogenicity of the organic layers following the European morpho-functional classification of humus forms. Concentrations of the metals increased with forest litter depth, reaching a maximum at the boundary between the organic and organic-mineral horizons (the difference exceeded an order of magnitude). In the same direction, the acidity increased, but the saturation of the exchange complex with Ca2+ and Mg2+ decreased. Within a particular forest litter profile, metal concentrations and acidity were lower in the layer with the highest zoogenicity compared to the layer with the lowest zoogenicity. Based on the metals, pH(water), and exchange complex, the accuracy of the predictions of the degree of layer zoogenicity within the OF horizon in the discriminant analysis reached 100 %. These findings suggest that the vertical gradient of toxic burden persisting in the forest litter after pollution cessation can explain the recovery pattern of humus forms in the contaminated areas.

Diversity and abundance of soil macroinvertebrates along a contamination gradient in the Central Urals, Russia

Background

Since the late 1980s, long-term monitoring of terrestrial ecosystems in metal-contaminated areas near the Middle Ural Copper Smelter has been carried out in the Central Urals. As a part of these monitoring programmes, the data on species diversity, community composition and abundance of soil macroinvertebrates continue to be gathered.

New information

The dataset (available from the GBIF network at https://www.gbif.org/dataset/61e92984-382b-4158-be6b-e391c7ed5a64) includes a 2004 census for soil macroinvertebrates of spruce-fir forests along a pollution gradient in the Central Urals. The dataset describes soil macrofauna’s abundance (the number of individuals per sample, i.e. the density) and community structure (list of supraspecific taxa, list of species for most abundant taxa and supraspecific taxa or species abundance). Seventeen sampling plots differed in the levels of toxic metal (Cu, Zn, Pb, Cd and Fe) soil contamination from air emissions of the Middle Ural Copper Smelter (heavily polluted, moderately polluted and unpolluted areas). The dataset consists of 340 sampling events (= samples corresponding to upper and lower layers of the 170 soil monoliths) and 64658 rows (2907 and 61751 for non-zero and zero density of taxa, respectively). Arachnida (Araneae and Opiliones), Carabidae (imagoes), Elateridae (larvae), Chilopoda, Diplopoda, Gastropoda, Staphylinidae (imagoes) and Lumbricidae were identified to species level. In contrast, Mermithida, Enchytraeidae, Lepidoptera larvae, Diptera larvae, Hemiptera, Hymenoptera and some other insects were identified to family or order levels. In total, 8430 individuals of soil macroinvertebrates were collected in two soil layers (organic and organic-mineral horizons), including 1046 Arachnida (spiders and harvestmen), 45 Carabidae, 300 Elateridae, 529 Myriapoda, 741 Gastropoda, 437 Staphylinidae, 623 Lumbricidae and 4709 other invertebrates. The presence-absence data on each taxon are provided for each sampling event. An overwhelming majority of such absences can be interpreted as “pseudo-absences” at the scale of sampling plots or study sites. The dataset contains information helpful for long-term ecotoxicological monitoring of forest ecosystems and contributes to studying soil macrofauna diversity in the Urals.

Sheltering Role of Well-Decayed Conifer Logs for Forest Floor Fungi in Long-Term Polluted Boreal Forests

Coarse woody debris (CWD) provides food and shelter to a large proportion of forest biota and is considered vital for biodiversity during periods of harsh weather. However, its importance in long-term stressed ecosystems remains largely unknown. In this work, we explored the contribution of CWD to fungal diversity along the gradient of boreal forest degradation caused by 77 years of heavy industrial emissions. We analyzed the diversity and composition of fungi in 270 samples of well-decayed Picea abies and Abies sibirica logs, as well as forest litter both adjacent to and distant from the logs. Compared with forest litter, the wood had higher water content and possessed substantially lower concentrations of heavy metals, which suggests its potential favorability for biota in polluted areas. The pollution-induced loss of fungal diversity in forest litter reached 34% and was stronger in the microhabitats not influenced by CWD. Meanwhile, wood fungal communities lost less than 10% of their total richness and even increased in alpha diversity. These processes led to the diversity and compositional convergence of fungal communities from different microhabitats and substrates in polluted areas. Despite this, the importance of wood and CWD-influenced microhabitats for fungal diversity maintenance was low. Apart from wood-associated fungi, the taxa whose diversity increased in the wood of polluted areas were ectomycorrhizal fungi and eurytopic soil saprotrophs (Mucoromycota, Mortierellomycota, Eurotiomycetes, and Helotiales) that easily tolerate highly toxic litter. Within the majority of pollution-sensitive soil saprotrophic groups, only terricolous Tricholomataceae benefit from CWD as microrefugia. Upon considering the ecological variability within low-rank taxa, the importance of decayed logs as safe sites can be high for certain soil-inhabiting fungal groups in polluted areas.