Albic Podzols of Boreal Pine Forests of Russia: Soil Organic Matter, Physicochemical and Microbiological Properties across Pyrogenic History

Abstract

Albic podzols under pine forests are more prone to fires on the planet. The influence of fire extends to all soil components, including chemical properties, microbiological characteristics, and the composition and structure of soil organic matter, which persists for a long time. Here, we present the results of a study of the morphological, physicochemical, and microbiological properties and features of soil organic matter (SOM) in the albic podzols of pine forests (Pinus sylvestris L.) not exposed to fires for a long time (from 45 to 131 years). The study areas are characterized by different numbers of old fires (from four to five) that occurred over the previous several centuries in various territories of the Russian Federation such as Central Siberia (CS) and the European North (EN). In general, the albic podzols developing in CS and EN are characterized by similar morphological and physicochemical properties, with high acidity and poor mineral horizons. In terms of the lower vegetation layer and stand parameters, forest communities at the CS sites have a lower density and species diversity than those in EN. The ground cover is almost completely restored 45 years after the surface fire. The upper mineral horizon of albic podzols in EN contains higher PAHs in comparison with similar horizons of the CS sites. In the soil of EN pine forests, the MB content in the mineral horizons is, on average, three times higher than those in CS. Differences were also found in the qualitative composition of the studied soils’ microbiomes. The EN soil communities are represented by a wide variety of bacteria and fungi. The presented soil parameters can be used as a reference in assessing the increasing impact of fires on pine forests and podzols.

Introducing a New Pyrogenic Podzolic Sub-Horizon to Clarify Organic Matter Pools in Pine Forest Soils

“…The upper section of the podzolic horizon Epyr, which lies beneath Oepyr, contains a mixture of charcoals. Total C varies from 1%-8%, while C/N is 20-38 [8]. Our proposal is to classify this layer as a separate organic-mineral pyrogenic sub-horizon called Eopyr as it was noted above.…”

“…scientific literature [24] and as Epyr in English [14]. Th horizon Epyr, which lies beneath Oepyr, contains a mix from 1%-8%, while C/N is 20-38 [8]. Our proposal is to organic-mineral pyrogenic sub-horizon called Eopyr as .…”

“…The total forest area in the Leningrad Region amounts to 4,667,000 ha with only 0.1% being recently burnt sites (http://www.priroda.ru accessed on 5 May 2023). The Albic Podzols [7] are the most widespread soil type found in pine forests, covering approximately 7% of the territory of the Russian Federation [8].…”

“…There is a dearth of research on the thin pyrogenic layers that lie beneath the forest floor on the mineral soil surface, comprising a mixture of charcoal, detritus, humus, and mineral particles. In scientific literature, the terms 'litter' and 'forest floor' both refer to a surface organic horizon measuring up to 10 cm, but neither has been sufficiently studied [1,2,8]. While the three terms have been used interchangeably, this paper deems 'forest floor' as the more accurate option.…”

“…Depending on its carbon content, the pyrogenic layer may be either organic or organomineral. For instance, in the Komi Republic, the profile of Albic Podzols was determined as Oi/Qpyr-Oepyr-Epyr-E-Bs-BC [8]. The study sites consisted of a lichen-covered pine forest with dwarf shrubs, including Vaccinium vitisidaea and Ledum palustre.…”