Yu. F. Arefjev,

Doctor of Biol. Sciences, Professor

Voronezh State University of Forestry and Technologies named after G.F. Morozov

Autoregulation of pathogenesis in forest ecosystems

INTRODUCTION

Autoregulation, understood as a process within biological systems, resulting from an internal adaptive mechanism and working to adjust or mitigate that system's response to stimuli, is one of the most important properties of biological systems. The modern forest ecosystems of the Central Russian forest-steppe not fully correspond to this property. Sporadic mass premature dying off of wood plants, excessive reproduction of some pathogenic organisms and insufficiency of natural renewal of the main forest forming breeds, show it convincingly. The purpose of the conducted researches is strengthening of the natural ecosystem regulating mechanisms for suppression of populations pathogenic for the wood organisms. Achievement of this purpose is closely connected with understanding of a role of forest structure in pathogenesis regulation.

METHODOLOGY

Viability of forest forming breeds and development of populations of pathogens were compared in relative to the heterogeneity of forest ecosystems. The level of heterogeneity was determined by Shannon's formula [1-5]:

,

где: H – the level of heterogeneity, i – element of heterogeneity, probability of an element, n – number of elements.

Model test object is askomyzetes Erisiphe alphitoides.

Viability of trees was estimated on the following scale: 5th point – healthy trees, without signs of considerable damages or dying off; 4th point – the weakened trees: krone is a little rare or (and) dim, smal defects of a trunk are possible; 3th point – trees are sick of the 1st degree: krone is considerably rare, major defects of a trunk are possible, the probability of recovery of health of a tree remains; 2th point – trees are sick of the 2nd degree: a krone is rare more than 50%, recovery of health of a tree is improbable); 1st point – the dying-off trees: only separate live elements remained. Recovery of a tree is impossible; 0 – point for the died-off trees.

The difference of results were compared by statistically reliable at p < 0,05; k = 10 %. .

RESULTS

It has been found that in heterogeneous ecosystems viability of the main tree species is higher, than in the homogeneous ecosystems (table 1).

Table 1

Viability of oak seedlings in various growth conditions

Growth conditions	Viability of oak seedlings, point
	Annual seedlings	Five-year seedlings
Heterogeneous: mixed group of oak, pine, birch plantings, H = 8,42 bits	4,31±0,02	4,23±0,01
Homogeneous: pure linear plantings of an oak, H = 2,41 bits	3,42±0,03	1,56±0,03

The success of natural regeneration depends on the abundance and survival of seedlings. The survival is better in heterogeneous growth conditions.

We have established that in rather small subpopulations of pathogens the effect of an inbreeding depression develops (table. 2). Inbreeding results in population homozygozygosity. Thus the chances of offspring being affected by recessive or deleterious traits can increase. Biological fitness of a population decreases. Inbreeding depression in our case suppresses population of E. alphitoides, its ability to survive and reproduce.

Table 2

Key parameters of generative bodies of E. alphitoides

in various growth conditions

Growth conditions	Parameters of generative bodies
	Frequency of kleystotetion, n/cm^2	Diameter of kleystotetion, µm	Length of konidiya µm	Width of konidiya µm
Homogeneous: pure linear plantings of an oak, H = 2,41 bits	64,3 ± 3,2	99,5 ± 5,3	32,7 ± 2,9	18,1 ± 0,9
Heterogeneous: mixed group of oak, pine, and birch plantings, H = 8,42 bits	8,7 ± 0,6	74,4 ± 3,1	24,8 ± 1,6	13,7 ± 0,8

Inbreeding is especially dangerous in small populations where the genetic variation is already limited. In our case the area of ecologically isolated plantings of ≈ 0,25 hectares is optimum (table 3).

Table 3

Development of E. alphitoides in various oak sites

Area of an oak sites, ha	Development, %		Selection volume, n	Variation coefficient,sx %
	Primary inokulyation	Konidial inokulyation
≈ 0,25	6	14	18	21
> 0,25	34	96	44	33

An optimal area of forests, at which the effect of decrease in density of a populyation of a pathogen is shown ≈ 0,25 ha. At the bigger area (> 0,25 ha) the effect of an inbreeding depression is not shown. Area of an oak sites less than a quarter of hectare (< 0,25 ha) is undesirable, as biotiс forest interrelations are broken [].

An internal adaptive mechanism works to adjust (mitigate) the development of E. alphitoides in heterogeneous growth conditions (tables 1 – 3). Main reason for the phenomenon is inbreeding. System's response to development of the pathogen and holds pathogenesis at rather low level. That is some degree of autoregulation. High-heterogeneous systems are more sensitive.

Autoregulation of genes is the heart of population autoregulation in forest ecosystems. The understanding of the phenomenon leans on fundamentals of population genetics. Genetic stability is provided in rather big populations. Small populations generate inbreeding and population depression.

CONCLUSION

Basic phenomenon of autoregulation of pathogenesis in forest eсosystems is inbreeding in pathogenic populations. The inbriding depression is caused by splitting of pathogenic populations into rather small subpopulations, approximately on the area of 0,25 hectares. High level of planting heterogeneity is adverse for excessive reproduction of pathogenic organisms. The populations of pathogens are maintained by autoregulation at almost admissible level. The viable populations of a forest tree species for the spontaneous development needs a larger areas.

Literature cites

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2. Arefjev Y.F., Senf V. A., Mamedov Ecological and genetic aspects of forest

phytopathology. Voronezh, 2017. – 115 p.

3. Brisbee K.E., Gower S.T., Norman J.M., Nordheim E.V. Environmental control on ground cover species composition and productivity in a boreal black spruce forest // Oecologia. 2001. Vol. 129. P. 261 – 270.

4. Shannon C.E. A mathematical theory of communication // The Bell System Technical Journal, 27 – 1948. – P. 379 – 423 and 623 - 656.

5. Heydenmann B. Zur Frage der Flächengrössen von Biotopbeständen für den Artenschutz und Ökosystemschutz // Jb. Naturschutz und Landschaftspflege, 31, 1981: 21 – 51.