Assessment of changes in the parameters of the leaf blade of heather shrubs in the post-pyrogenic area of the Great Vasyugan Mire

Every year, extensive areas of forest and mire are affected by fires. Following a fire, conditions for plant growth and development in the impacted area are altered for many years. The fire damages vegetation, disrupting the hydrothermal regime, increasing insolation, and accelerating biogeochemical cycles. This combination of environmental changes results in long-term alterations to the morphometric and physiological characteristics of plants. This study aims to assess the effects of a fire that occurred five years ago in a mire on the leaf characteristics of heather shrubs. The study focused on two raised bog sites located in the interfluve between the Bakchar and Iksa rivers, within the Great Vasyugan Mire. One part of the bog had been affected by a crown fire, which completely destroyed the tree layer and caused significant damage to the grass, shrub, and moss layers. Five years after the fire, the shrub layer had fully recovered; therefore, Rhododendron tomentosum Harmaja and Chamaedaphne calyculata (L.) Moench., the dominant species in the shrub layer of the study area, were selected as model species. Samples were collected twice in 2021: in May, mature leaves from the previous year were gathered, and in July, young leaves from the current year were also collected. Leaf mass per area (LMA), defined as the ratio of dry weight to leaf area, and the content of photosynthetic pigments were determined for these samples. The statistical significance of differences between groups was assessed using the Mann-Whitney test (p < 0.05). To establish relationships between variables, the Spearman correlation coefficient was employed. In this study, we demonstrated that the leaf mass per area (LMA) of the species examined was significantly lower in the post-pyrogenic area (See Fig. 1). The reduction in LMA can be attributed to changes in the hydrothermal regime and increased insolation resulting from the burning of the tree layer. The concentrations of carotenoids (See Fig. 2), chlorophyll a (See Fig. 3) and chlorophyll b (See Fig. 4) negatively correlated with LMA, with higher pigment levels observed in post-pyrogenic sites compared to pristine sites. This is facilitated by increased water availability for shrubs following fire and enhanced deposition of microelements in the upper peat layer, leading to differences in most leaf parameters between plants from post-fire and pristine sites. Consequently, plants from post-pyrogenic sites differ in most leaf blade parameters from those in pristine sites. The exception is the leaves of R. tomentosum collected in July, whose area does not differ between the two sites. Additionally, differences in carotenoid content in C. calyculata leaves sampled in July are marginally significant (Z = 1.9; p = 0.049). Leaves of shrubs collected in May from post-pyrogenic sites differ significantly from those collected in pristine sites across all examined indicators. Therefore, it is recommended to sample for morphometric parameters and photosynthetic pigments at the beginning of the growing season. After a fire, soil in mires warms more rapidly, causing plants’ phenological stages to commence earlier and not coincide with those in pristine mires. The surface area of young leaves sampled in July has not yet reached its maximum in pristine sites, which explains the lack of significant difference from that in post-pyrogenic sites. As a result, five years after the fire, we can conclude that the parameters of plant leaf blades retain signs of adaptation to changing conditions, as evidenced by a decrease in LMA and an increase in pigment content at the post-pyrogenic site. The article contains 4 Figures, 1 Table, and 39 References. The Authors declare no conflict of interest.