The State and Biochemical Composition of Coniferous Plant Wood in Places of Degradation

Background. A signicant deterioration in the state of dark coniferous forests, which in some cases is accompanied by their drying, has manifested itself throughout the Northern Hemisphere. This process is very dynamic and covers the entire boreal zone from Europe to the North American continent, covering all forest-forming species Research in the eld of the ecological biochemistry of wood opens up wide possibilities for studying the stability of spruce stands. Coniferous wood, including spruce, consists of polymer structural components (cellulose, hemicellulose and lignin) and non-structural components (including extractives, ash and other minor substances). Extractives with high biological activity, which are produced as protective compounds during the life of plants from external environmental stresses, play an important protective function in coniferous wood. The structure of wood and its biochemical composition can change under various inuences. The content of extractives varies greatly not only in different areas, but also from specimen to specimen, depending on their condition. In this regard, the aim of our research was to study the content of extractives in spruce wood in specimens of different life states. Methods. This work presents the results of studies on the characteristics of the biochemical composition of Siberian spruce (Pícea obovata L.) in mass drying conditions in the territory of the Udmurt Republic (Russia). The enumeration method was used to create a plot taxation. A study of the biochemical composition of wood was carried out based on the content of extractives from specimens in various life states. Results. Trial plot stands are characterized by low tree density in the main canopy. According to biochemical analysis, the highest content of extractives was observed in specimens with good and satisfactory vitality. In trees with an unsatisfactory life state, biochemical parameters were low, which is associated with the lack of self-regulation in dead wood. Obviously, the under study of Pícea and their a


Background
The importance of dark coniferous stands of the Northern Hemisphere is their global role in the distribution of organic carbon, where they play a conservation role (Taylor et al. 2007). A signi cant deterioration in the state of dark coniferous forests, which in some cases is accompanied by their drying, has manifested itself throughout the Northern Hemisphere. This process is very dynamic and covers the entire boreal zone from Europe to the North American continent, covering all forest-forming species (Bahtenko, 2008;Rysin, 2009). The mass drying of spruce over a large area of the European part of the Russian Federation after abnormally high temperatures in 2010 caused considerable interest among researchers studying the problem of spruce stand resistance to adverse environmental conditions, anthropogenic stress, pests and diseases (Ivanchina & Zalesov, 2017;Negrón, 2018). Research in the eld of the ecological biochemistry of wood opens up wide possibilities for studying the stability of spruce stands. Coniferous wood, including spruce, consists of polymer structural components (cellulose, hemicellulose and lignin) and non-structural components (including extractives, ash and other minor substances). Extractives with high biological activity, which are produced as protective compounds during the life of plants from external environmental stresses, play an important protective function in coniferous wood. The study of extractive substances in wood is most actively carried out in foreign countries to understand their nature and role as natural activity inhibitors for woody microbiota (Korotkov et al. 2014). Good literature reviews on extractives are presented in foreign works (Scheffer,  The structure of wood and its biochemical composition can change under various in uences. Therefore, to identify patterns, it is necessary to have a relatively clear idea of the in uence exerted by individual environmental factors. The content of extractives varies greatly not only in different areas, but also from specimen to specimen, depending on their condition (Prusakova et al. 2008). In this regard, the aim of our research was to study the content of extractives in spruce wood in specimens of different life states.

Materials And Methods
The researchwere carried out on the territory of the Udmurt Republic (here in after the UR). The area of the republic is 42.06 thousand km 2 . Udmurtia is located in the European part of the Russian Federation, in the basins of the Kama and Vyatka rivers, west of the Ural Mountains, between parallels 56°00' and 58°30' north latitude, and meridians 51°15' and 54°30' east longitude. The territory ofthe URstretches broadly north to south for about 320 km, and west to east for 200 km. Signi cant elongation of the territory from north to south and hilly-rugged terrain causes major differences in temperature, humidity, wind, and rainfall between the northern and southern parts of the republic. In this regard, the territory of the UR is located within two landscape zones: taiga (boreal/south-taiga zone) and subtaiga (borealsubboreal/coniferous-deciduous forest zone). Its border coincides with the northern border of a range of Quercus and Corylus; it is conditionally drawn between the settlements of the republic of Vavozh -Nylga -Izhevsk -Votkinsk (Fedorova et al. 2016) (Fig. 1).
To assess the taxation parameters and the condition of spruce stands, 100 × 100 m sample plots were laid. The test plots (here in after -TP) were laid in two forest districts (Zavyalovo and Yagan) located in the subtaiga zone (boreal-subboreal/coniferous-deciduous forest zone). In each forest district, two trial plots were laid. Trial areas were laid in standspredominantly made up of spruce where they are actively drying out, and in acidic types of forests. The soils in the trial plots are sod-podzolic, and loamy in granulometric composition. Trees were divided into three groups based on their life state: 1) good (the crown is thick or slightly sparse, the needles are green/light green; individual branches have dried up); 2) satisfactory (openwork crown; needles light green); 3) unsatisfactory vitality (needles are yellowish, up to 2/3 of the crown with drying branches; fruiting bodies of fungi, presence of hollows, dead specimens). To study the biochemical characteristics of wood, three specimens were selected within each group.
Wood samples were taken only from Siberian spruce (Picea obovata L.). Cores were taken using an age drill at a height of 0.3 m from the root neck of the tree. Coniferous extractives were fractionated in accordance with their chemical nature by sequential extraction with solvents of increasing polarity. The extractives were identi ed using hot distillation in a Soxhlet apparatus -water-soluble substances with hot water, resinous substances with an alcohol-toluene mixture. The tannin content was determined using the permanganometric method (Babkin, 2017). The analyses were carried out in the laboratory of Ecological and Fire Safety of the Federally Funded Educational Institution of Higher Education Udmurt State University (Izhevsk).
Sample variance analysis was used to estimate the signi cance of sample differences (Lakin, 1990). Mathematical processing of the results and visualization of the data was performed in the statistical analysis environment R (Mastickij, 2015).

Taxation Characteristics
An analysis of the distribution of trees by diameters relative to the average revealed a regular distribution of plants in the main canopy. Comparing the diameters of living and dead spruce specimens revealed that most of the dead trees have a trunk diameter above average. In terms of productivity, it was established that TP plantings belong to productivity class III. The average taxation characteristics of the stands on the studied TP are presented in Table 1.     The plantings on the trial plots are characterized by low tree density in the main canopy. The density varies from 2.95 to 11.1 m 2 /ha with a large number of dead trees (absolute density, taking into account dead trees, 5.9 ... 17.9 m 2 /ha). Stands with similar density are described as woodlands.
The enumeration taxation in all study areas revealed a rather large amount of dead wood. Depending on the TP, its stock was 31.1 ... 93.8 m 3 /ha, which increases the risk of forest res. In the trial plots in the Yagan Forest District, the stock of dead wood exceeds the stock of living trees, and in the Zavyalovo Forest District, dead wood accounts for more than 50% of the living wood stock.
Thinning of the main canopy led to a change in the plant community. In the living ground cover, nemoral forest herbs (European ungulate (Asarum europaeum L.) and wood sorrel (Oxalis acetosella L.) begin to be replaced by eld forbs ( eld sow thistle (Sonchus arvensis L.), cat grass (Dactylis glomerata L.), Kentucky bluegrass (Pao pratensis L.), hybrid clover (Trifolium hybrídum L.) and others).
New conifer growth was not present on test plots in the Yagan Forest District, and was present on test plots in the Zavyalovo Forest District, but was insu cient (less than 500/ha) and of poor quality (not hardy). Woody vegetation included common raspberry (Rubus idaeus L.), mountain ash (Sorbus aucuparia L.), forest honeysuckle (Lonicera xylosteum L.), and silver birch (Betula pendula Roth.), the latter of which is beginning to form the main canopy.

Extractives Content
A comparative study of the total content of extractives in wood in three spruce groups revealed signi cant differences (p < 0.001), which mainly lie in the content of resin and tannins in trees of satisfactory and unsatisfactory vitality (p < 0.000); no signi cant differences (p > 0.05) were found in the "water-soluble extractives" group. The highest content of all groups was found in plants with a satisfactory life state, and the lowest was in dry trees (Fig. 2).
A study of the content of extractives in various TPs revealed that both the total content of and individual types were statistically signi cant only for TP3 and TP4 (p < 0.005), which are located in the Yagan Forest District. For the test plots in the Zavyalovo Forest District, no signi cant differences were found for any category of extractives (p > 0.05).
When analyzing the combined in uence of both grouping factors (in terms of vitality and TP), it was found that the greatest difference in average values for extractives composition is associated with tree vitality (p < 0.001) while habitat plays a smaller role (p < 0.01); the exception is resinous content (p < 0.000). Variance analysis indicated that the interaction between the two factors is insigni cant. Each of them has a separate impact (Fig. 3).

Discussion
Thinning of the main canopy is the main environmental factor that leads to a change in the plant community. Based on the data obtained, it can be said that mass drying has resulted in the trial plots losing the main features of spruce forest ecosystems. Birch and other deciduous species are beginning to form the main canopy. Meanwhile, there is mass growth in meadow vegetation, which forms dense groundcover that does not allow spruce seedlings to take root. All

Conclusion
This research allows us to state that an active change in the plant community in coniferous stands is underway as a result of the degradation of the main canopy. Spruce plantings are characterized by low tree density in the main canopy which is facilitating a natural succession from dark coniferous forests to soft-leaved ones. The combination of these factors forms a favorable environment for the bark beetle population to spread (Ips typographus), which is the main cause of death for spruce in the territory of the UR. One internal mechanism in response to external stress factors (including damage to organs by phytophages) is the intensi cation of the formation of internal metabolites, in particular tannins and resins. The results of our biochemical analysis of wood showed that one of the factors determining the content of extractives in wood is tree vitality. It is likely that a high content of tannins and resins in weakened trees indicates that the plant's internal resources were mobilized. In this way, the content of extractives can be an indicator of the conditions of spruce species and can be used in the selection of trees to create sustainable plantings in forest cultivation. However, for a more complete understanding of the dynamics of extractives in trees in various states, a series of additional studies and data calibrations are necessary that account for seasonality, climatic factors and the degree of damage caused by pathogenic agents.

Declarations
List of Abbreviations Availability of supporting data The tree regions and associated tree attributes used in the study are available from the corresponding author on reasonable request The average content of various groups of extractives in Siberian spruce (Picea obovata) L.) in relation to various factors: A is total content of extractives; B is water-soluble extractives; C is tannins; D is resinous extractives. Designations: F1 -test plot (TP): tp1 -TP1, tp2 -TP2, tp3 -TP3, tp4 -TP4. F2 -vitality: g -good vitality; m-satisfactory vitality; p -unsatisfactory vitality