Microhabitat distribution of arboreal oribatid mites (Oribatida), associated with the Siberian pine (Pinus sibirica) of Western Siberia.

Study Extent

Two forest biotopes were studied in the Pur River Valley, in the vicinity of the town of Urengoy. The first biotope is classified as a “sparse spruce-birch-cedar shrubwood forest-tundra with the presence of sedge and moss”. The forest stand formula is 6C2B1S, the quality of locality is 4 (65° 57'39 "N, 78° 16'35" E). The degree of leaf canopy density is 20%. The distance from the nearest water body to the sampling point is about 100 m. The trees, from which the samples were taken, are protected from all sides from strong wind. The second biotope is described as an “azonal floodplain birch-spruce-cedar forest-tundra with mesophytic grasses”. The forest stand formula is 8K1E1B, the quality of locality is 4 (65° 56'36 "N, 78° 20'35" E). The degree of leaf canopy density is 60%. The samples were obtained on the river bank, where trees were not protected from strong winds coming from the south. The region is located on the border of the Subarctic and Temperate continental climatic zones. The average monthly air temperature in January and July in this area is -26.4 ° C and + 15.4 ° C, respectively. The average monthly temperature of the soil surface is -28 ° C in January and +18 ° C in July. The average annual wind speed is 4.2 m / s. The average annual relative humidity of air is 76%. The annual amount of liquid and mixed precipitation is 286 mm. Other terrestrial ecosystems will be described later.

Sampling

Sampling In July, 2015, in each biotope, I randomly selected three trees of Siberian pine Pinus sibirica for sampling. Samples were taken according to a previously tested technique, which was slightly modified (Tolstikov and Bragin 2001). I took three standard samples of litter with a volume of 125 cm3, near the base of each tree with a cylindrical sampler. Then, three samples of bark were taken from the bole of the tree (from 0 to 2 m). The first sample from the trunk portion was from a 0 to 40 cm height, the second was from the 40 cm to 1 m height, and the third one was from the 1 to 2 m height. All bark samples were taken from the south-eastern side of trees. The sampled area was 100 cm2 in each case. After that, the crown of the tree was divided into three zones: the lower (from 3 to 7 m), the middle (from 7 to 11 m) and the upper one (above 11 m). From each zone I obtained a sample of: trunk bark; the needles; young branches with needles; young branches without needles; older branches; the bases of the branches near the trunk of a tree; dead branches. I collected the bark as follows. I applied a 10 x 10 cm aluminum frame to the trunk; traced it with white chalk; and then cut out all of the outer bark inside the frame with a knife. A sheet of white cardboard was positioned below, from which, all the pieces of bark were shaken into the bag. The branches were cut using a hand pruner and a pocket saw. Each sample included 10 branches, with a length of about 10 cm (except for the samples of branch bases, for which two parts of the branch were sawed off).
The needles were cut with scissors, leaving 5 mm or less on the branches. This was necessary to exclude the possibility of accidental falling of mites from the sheaths of the needles into the samples of needles. Extraction of oribatid mites. The Tullgren-Berlese funnels were used to extract mites from the litter samples into alcohol. The local heating of the substrate was not applied. The mites were extracted from the bark, branches, and needle samples using a modified heptane flotation method, described in (Tolstikov and Bragin 2001). The sample was placed in a container with a solution of caustic sodium, where it was soaked for about 10 minutes. Then, the contents was poured into a stack, consisting of two laboratory sieves with a diameter of 20 cm and a mesh size of 0.8 and 0.08 mm. After that, each branch and each large piece of bark were washed on top of a sieve with a strong stream of water. The water was sprayed out of a special perforated nozzle, attached to a hose, which was connected to a water tap. Needles and small pieces of bark were washed in bulk, turning over several times on a sieve. All the residue on the lower sieve was deposited into a 100 ml glass measuring cylinder. Then, several milliliters of heptane or octane were poured into this cylinder. The water was added so that the cylinder was filled to 4/5 of its volume. The cylinder was plugged with a rubber stopper, after which its contents were shaken intensively for 30 seconds. After that, the contents of the top portion of the measuring cylinder were poured onto a stack of sieves with different mesh diameters. The sieves were arranged in a descending order of mesh size: 0.5; 0.4; 0.315; 0.25; 0.2; 0.16; 0.14; 0.125; 0.1, and 0.08 mm. The material that accumulated on each sieve was then pressure-washed, as described above. The number of sieves in a stack was selected depending on the volume of the floated material. The quantity of sieves was such that a moderate amount of material remained on each sieve. In particular, I wanted the material to form only one layer on the filter paper circle with the particles being separated by a distance not exceeding their size. This procedure was necessary to increase the likelihood of finding mites. The contents of the surface of the discs were viewed under a stereo microscope "Zeiss SteREO Discovery.V8". Mites were identified in temporary slides, with the help of lactic acid, using the Zeiss AXIO Lab.A1 microscope.

Method steps

1. In this study, I used the values of the relative abundance of oribatid mites, expressed as the number of individuals per square meter of substrate (ind./m2). To calculate the area of branches, I used the formula S= πdh, where d - is the diameter of the branch cut in the central part and h - is the length of the branch. The statistical analysis of the data was performed in the PAST 3.15 software. In addition, Microsoft Excel was used for data preparation and simple calculations. To identify the differences among microhabitats in terms of the overall abundance and species diversity, I used the Kruskel-Wallis test, which allows comparing several non-normally distributed samples. In pair comparisons, I used the Mann-Whitney test with the Bonferroni correction as a posteriori test. The results of statistical tests were considered significant at a significance level of less than 5%. We have identified domination groups according to the classification proposed by Engelmann (Engelmann, 1978): eudominants - 40-00%, dominants - 12.5-39.9%, subdominants - 4-12.4%, residents - 1,3-3.9%, subresidents - <1.3%. Species diversity in litter and arboreal microhabitats were calculated as the average value of the Simpson’s index (1-D) in each sample. I used multidimensional non-metric scaling (NMDS) to identify groups among litter samples and all arboreal microhabitats, after which I conducted a non-parametric analysis of variance (PERMANOVA) to test the statistical significance of the differences between the groups. A matrix of dissimilarities among samples was generated based on the Bray–Curtis index (Magurran, 2004).

These are terrestrial ecosystems of taiga and forest-tundra in Western Siberia.