BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

XIV. INSTRUMENTATION AND METHODS FOR STUDYING AQUATIC VEGETATION

Determination of phytomass and production in plant communities.

No matter how important the determination of macrophyte production is, methodologically this problem has not yet been fully resolved due to the complexity and labor-intensive Nature of the work. There are both "direct" and "indirect" Methods. All modifications of the direct method boil down to determining production based on the maximum above-ground phytomass using P/B coefficients. In most cases, above-ground phytomass is determined in fresh and air-dry states.

Studies on the biology of individual species show that they reach their biomass maxima at different times and during different phenophases [46, 65e]. Some of them are characterized by significant growth rates [103], while others are marked by The formation of multiple generations throughout the vegetative season [36]. However, for most species, the phytomass maximum occurs during the flowering period, i.e., from July to early August.

Above-ground phytomass is most conveniently determined in sample plots or transects no wider than 0.5 m. The number of control plots and their sizes depend on the Structural Features of the grass stand and the desired accuracy of the results. Typically, mowings are harvested from an area of 0.25, 0.5, and 1.0 m1. In communities of rooted plants with floating leaves, the size of the sample plot is increased to 2-4 m . If special devices (dredges, bottom grabbers, etc.) are used to collect quantitative vegetation samples, the number of their immersions must be sufficient to cover an area of 0.25 or 0.5 m . In multi-species thickets of mosaic composition with a sparse grass stand, more mowings need to be taken than in monodominant communities with a dense grass stand. More accurate results are obtained when A large number of mowings are taken from small plots rather than vice versa. V. I. Vasilevich [9a] proposed a formula for calculating the required number

of mowings to obtain the average phytomass value with a given accuracy N = V /р , where N is the number of mowings, V is the coefficient of variation in the sample, and р is the desired accuracy. According to this formula, to determine the fresh and air-dry phytomass of most plants in the Kremenchuk Reservoir with an accuracy of 10%, it is necessary to collect 20 mowings of 1 m each [41]. When increasing the accuracy to 15%, the number of mowings increases to 25-40 (in some cases up to 70-80).

V. G. Papchenkov [65] suggested that when studying the aquatic vegetation of a region, average phytomass values should be determined for different classes of projective cover (up to 30%, from 30 to 60%, from 61 to 90%, above 91%). In such cases, if a geobotanical Description of the aquatic vegetation with specified projective coverages of species is available, the biomass of phytocoenoses can be calculated without harvesting mowings.

A plot exceeding 1 m1 in area, from which vegetation is removed to determine phytomass, is bounded by a special collapsible frame made of a non-floating material, or by a cord. At shallow depths (up to 0.6-0.8 m), submerged plants and plants with floating leaves are collected by hand, while emergent plants are cut right at the bottom. Care should be taken to remove plants (especially submerged ones and those with floating leaves) that are rooted far beyond the BOUNDARIES OF THE sample plot. When taking a sample at a depth exceeding 1 m, the frame must be securely anchored with pegs at the corners to avoid increasing the sample area. This should be done from a boat, preferably by two people. To cut plants at such depths, a scythe with a short blade is used. Mowing begins from the center of the plot; after every 12 strokes of the scythe, the cut plants are gathered by hand or with a landing net. Plants can be mowed down to a depth of 1.5–2.5 m; under such conditions, it is desirable that the shaft of the scythe resting on the bottom rises 1.0-1.5 m above the Water. As noted above, the most accurate sampling of submerged plants at great depths is possible only with the aid of diving equipment, in which case the frame is made of metal.

When sampling helophytes and pleustophytes at great depths, a simplified method is sometimes used: the average mass of a single SHOOT or leaf with a petiole is determined and multiplied by their number per unit area. As a rule, the average plant mass is determined from 10-15 shoots; for a more accurate determination, the aforementioned formula by V. I. Vasilevich can be used.

During the Processing of samples, plants are washed free of mud and cleared of epibionts as much as possible. For transportation, they are packed in plastic bags or gauze "diapers" wrapped in plastic on the outside. It is advisable to process the samples within 24 hours of collection. First, dead plant debris is separated, and "live plants" are weighed (with an accuracy of 510 g) after preliminarily freeing them from excess water. Then the sample is sorted by main species, and for each of them, weighing and various measurements are carried out depending on the objectives set. For a more accurate determination of phytomass and subsequent calculations, In addition to fresh mass (FM), air-dry mass (ADM) and absolute dry mass (ODM) are determined. Drying to ADM is carried out in the air or indoors. Drying time depends on the condition of the sample, Temperature, and air humidity (emergent-aquatic plants dry within a week).

Weighing is carried out after complete drying, which is determined visually (leaves break when bent) or by repeated weighing until constant mass is reached. In the laboratory, a ground plant sample is weighed to an accuracy of 0.1 g and dried in a drying cabinet at 65° C to a constant mass. The percentage of free moisture in the plants is determined from the mass difference. After this, the sample or a part of it is weighed on an analytical balance to an accuracy of 0.001 mg and dried to a constant mass at 80-105° C. This is how ODM is calculated, and the bound moisture content is determined from the mass difference before and after drying. Afterwards, a weighed portion of the dried plants is incinerated in a muffle furnace to determine (as a percentage) the ash and organic matter content. If plants are covered with a "carbonate crust", a correction factor is used for accurate phytomass determination. It is calculated by comparing the ODM of the sample with carbonates with the ODM of "washed" plants, for which the latter are placed in a 3-5% Hydrochloric acid solution for a few minutes and then rinsed with water.

In the practice of hydrobotanical research, phytomass is usually measured in ADM. If only FM is known, conversion factors calculated for the given region or obtained independently are used to convert it to ADM. Phytomass is expressed in g/m , c/ha, and t/km .

Above-ground phytomass reserves (total phytomass) are determined based on the average phytomass per species and the area it occupies. Another calculation method takes into account the phytomass and areas of thickets with different densities. Phytomass reserves are measured in ADM and ODM in kg, c, and t.

In established thickets of aquatic macrophytes, underground phytomass often exceeds above-ground phytomass by several times. However, it forms over the course of several years and does not play a major role in creating the total annual production. According to Westlake, Meral [14z], the rhizomes of reeds and bulrushes function for 4 years, and those of cattails and bur-reeds for 1.5-2 years. Work on determining underground phytomass is technically extremely difficult and is carried out only in special studies. Underground phytomass is calculated from the above-ground part taking into account approximate percentages obtained by D. Wetzel [145].

As a rule, net primary production of macrophytes is determined by multiplying the total phytomass values by a P/5 coefficient, which accounts for losses associated with leaf fall and the consumption of other vegetative Organs by heterotrophic organisms. To obtain accurate values of the P/5 coefficient for various plant species and water bodies, special studies are conducted on permanent plots throughout the vegetative season.

The methodology for such work is described in detail by E. V. Borutsky [8]. Typically, when studying The production of higher aquatic plants, a coefficient of 1.2 derived by I. M. Raspopov [75] is used. V. G. Papchenkov [65] suggests using this coefficient only for tall-grass helophytes (sweet flag and sedges - 2.0); low-grass helophytes - 2.3; hydrophytes of stable lake biotopes - 2.5, and under conditions of watercourses and reservoirs - 4.0; for filamentous Algae, a coefficient of 10 is adopted [9a].

Underground production of young thickets and peripheral areas of mature communities accounts for 50% of the underground phytomass, while in old ones it is 20-25%. The same ratio is characteristic of water-lilies. In calculations for submerged rooted plants, it is advisable to use a coefficient of 0.5 for old thickets and 0.8 for young ones.

Phytoproduction is best expressed in energy units; for this purpose, it is first converted into units of organic matter or carbon. K. A. Kokina [41] provides data showing that in emergent-aquatic vegetation, the organic matter content is 92% of ODM, in floating-leaved vegetation - 90%, and in submerged vegetation - 85%. According to [121], 1 gram of absolutely dry matter corresponds to approximately 0.4 g of carbon or 4 kcal (in the International System of Units SI, 1 cal = 4.19 J). This is an average value, since the energy equivalent of plant mass depends on the plant species and its stage of development. In charophytes, filamentous algae, and mosses, 1 g of ODM is roughly equivalent to 1.2-2.9 kcal, while in pondweeds, Elodea, and marsh horsetail, it is 3.3-4.0. During hydrobiological studies, total phytoproduction, Production of organic matter, carbon, and production in energy units are usually calculated per unit area of the water body, shallows, thickets, and also per unit volume.

Indirect Methods for determining production are based on measuring The rate of Photosynthesis per unit of time (oxygen and radiocarbon methods).