STUDIES ON THE ECOLOGY OF ALDROVANDA VESICULOSA L.I. ECOLOGICAL DIFFERENTIATION OF A. VESICULOSA POPULATION UNDER THE INFLUENCE OF CHEMICAL FACTORS IN THE HABITAT

EKOLOGIA POLSKA 35: 559-590 (1987)

Ryszard KAMIŃSKI

Botanic Garden, University of Wrocław, Sienkiewicza 23, 50-335 Wrocław, Poland

ABSTRACT: Ten habitats of A. vesiculosa - disappearing in Europe aquatic plant, have been investigated. The habitats were characterized according to water chemistry, composition of bottom sediments, describing also the coenotic relations, i.e., biotic ones in the phytosociological aspect. An analysis of individual and group characters of plants allowed to find chemical factors of habitats most significant for the growth of plants examined, the best habitats for A. vesiculosa population were indicated, also water chemistry necessary for maintenance cultures or introductions was determined.

KEY WORDS: Aldrovanda vesiculosa, ecological differentiation of population, chemistry of habitats, humic acids, coenotic relations, introduction.

INTRODUCTION

Changes in natural environment causing the death of many plant species make it absolutely necessary to study more intensely their ecology and to find methods for their protection. Legal protection of endangered species is no longer sufficient. Active protection requires an interference in the fate of each endangered population of the disappearing species, and the least we can do is to find a substitute place. Therefore, it is indispensable to know the best physico-chemical and biotic conditions in the habitat.

At present the most endangered are water and marsh-plants as each interference of man frequently causes irreversible changes of aquatic relations in the habitat and of water chemistry. One of such plants is Aldrovanda vesiculosa - small, free floating, belonging to the family Droseraceae and thus carnivorous. Another interesting thing is that it cannot grow in a purely mineral range (A s h i d a 1934, 1935, S c u 1 t h o r p e 1971), but requires the presence of organic matter or accompanying plants. Its range of occurrence is rather wide (Europe, Asia, Africa, Australia), although the number of its localities is relatively small. The majority of them have been in Europe, but are no longer confirmed (acc. to IUCN data).

Fig. 1. Distribution of localities of Aldrovanda vesiculosa and those that should be verified in Poland

As the highest number of localities of A. vesiculosa in Europe was recorded from Poland I tried to determine the resources of this species in Poland. The exploration conducted between 1979 and 1981 covered 35 localities out of 74 known ones as the probability of finding the plant there was the greatest. The occurrence of A. vesiculosa was confirmed only on 12 localities (K a m i ń s k i 1983). Autecological investiga­tions on 10 localities (Fig. 1) were conducted to provide answers:

(1 ) What is the ecological amplitude of A. vesiculosa, i.e., to what extent its habitats are differentiated, especially as regards water chemistry?

(2) Are the group and individual characters of natural A. vesiculosa populations differentiated and to what extent it is conditioned by the chemistry of habitat? Thus, it would be known what kind of habitat is the most suitable for this plant, and what are the worst factors affecting the plant populations causing their disappearance from particular localities.

METHODS OF INVESTIGATIONS

2.1. PHYTOSOCIOLOGICAL ANALYSIS OF A. VESICULOSA LOCALITIES

The phytosociological analysis, based on the system of M a t u s z k i e w i c z (1982) for precise definition of plant associations, among which A. vesiculosa occurs, included a comparison of 20 geobotanical records made by the Braun-Blanquet method (Matuszkiewicz 1967). Their area varied, depending on the area occupied by the population of the plant examined. They were in patches of communities with the highest density of populations examined.

2.2. CHEMICAL ANALYSIS OF WATER AND BOTTOM SEDIMENTS

Each microhabitat of Aldrovanda on localities examined was described according to the chemical characteristics of water and bottom sediments. Three samples of water from each microhabitat were taken at the depth of 5 - 20 cm at the turn of July in 1980 and 1981. Water pH was determined directly on localities. For nitrogen determination water was preserved with 3 ml CHC1₃.1^-1 (G o m ó ł k a  and  S z y p o w s k i 1975) and for iron - with muriatic acid, 12 ml.l^-1 of water (H e r m a n o w i c z  et al. 1967). Before the analyses all samples were stored at 2°C.

The contents of nitrates, ammonia (using Nessler's reagent), phosphorus in the form of orthophosphates and iron were determined by the colorimetric method in water. The flame photometer (Johanson-Ulrich method) was used to determine the contents of potassium and natrium, EDTA method - for calcium and magnesium, nephelometric method - for sulphates and titration for chlorides. These methods are given by Hermanowicz et al. (1967), Lurie (1973), Gomółka and Szypowski (1975).

Total contents of organic substances, expressed by carbon content in water volume, were determined by a simplified method of Kononova and Belčikova. Carbon was determined in dry residue after the evaporation of previously filtered water in water bath at 60°C. The contents of free and connected with free-forms R₂O₃, i.e., not connected with calcium, of humic and fulvic acids were determined by Tjurin's method. Both methods are described by  K o n o n o v a (1968).

In bottom sediments, presenting very well the trophic state of habitats, the contents of organic matter, calcium carbonate and silicates were determined by gravimetric method (L i t y ń s k i  et al. 1972).

2.3. CHEMICAL ANALYSES OF PLANTS

Plants were sampled together with water from places varying as to the species composition of plants accompanying the Aldrovanda. Plants were incinerated with perhydrol and sulphuric acid. Then a water solution was made, in which nitrogen was determined by the turbidimetric method (N o w o s i e 1 s k i 1968), phosphorus ­by the colorimetric method with molybdate (B a b k o and P i 1 i p i e n k o 1955), potassium and sodium - in a flame photometer using the Johnson-Ulrich method, calcium and magnesium - by the EDTA method (B a r r o u s and S i m p s o n 1962) and iron - by the colońmetric method with alpha-alphabipyridyle according to P i p e r (1957). Sulphur was determined by the Butters-Chenry method (N o w o s i e 1 s k i 1968), whereas the ash content in dry plant weight - by combustion in a muffle furnace (600°C, 6 hours). All measurements were repeated three times.

2.4. SELECTION OF INDIVIDUAL AND GROUP CHARACTERS OF PLANTS AND THEIR MEASUREMENTS

The experimental areas were varying as to the species composition of accompanying plants. The size of experimental areas was 0.25 - 1.0 m², depending on the density of plants, 30 plants of A. vesiculosa being the minimum (with the exception of locality 1 at Nowa Kuźnia, where the experimental areas covered more than 200 m²). In the biometrical analysis each population was represented by three samples, i.e., 90 plants. The biometrical analysis included: plant length, number of whorls, mean length of internodes, number of leaves in a whorl (mean number of leaves in three middle whorls), length of leaves (mean of 3 measurements in middle whorls), number of setae (mean from visual inspection of 5 optional leaves), number of branches, their mean length and number of buds in leaf whorls. The measurements are given in millimetres.

As regards the group characters, i.e., the population ones of A. vesiculosa, analysed were: plant density, i.e., number of individuals per 1 m², biomass of 100 plants in mg dry weight as an indicator of habitat productivity in relation to Aldrovanda and the biotic population potential. The index of biotic potential was assumed as the ratio of the sum of buds, branches and young individuals to the number of plants in the sample. As young plants were accepted plants without the brown tints on leaves in the oldest whorls, so separated not long age from parent plants.

2.5. EXPERIMENTS IN CULTURES IN VITRO

Indispensable experiments in cultures in vitro were conducted to determine the effect of basic chemicals in the habitat on the growth of plants examined. Examined were apical plant segments, 30 mm long, from Lake Kruglak (experiment 1) and the pond at Nowa Kuźnia (experiment 2).

E x p e r i m e n t  1. It followed a series of preliminary experiments to determine the best medium composition and was conducted in two parts (A and B). The aim was to determine the effect of more important macroelements (ammonium and nitrate forms of nitrogen, phosphorus, potassium, magnesium and humic acids in the form of sodic humiane including the joint effect of humic forms and mineral compounds) on the growth of plants examined. In experiment A conducted between June 12 and July 7, 1981, a modified medium of Hampe and Truffaut was used (B u c z e k  et al. 1976) with an addition of microelements acc. to H e 1 1 e r (1953) and sodic humiane. The basic medium contained (in mg.l^-1): NO₃ - 0.62, NH₄ - 0.54, PO₄^3- - 0.47, K⁺ - ­3.12, Mg²⁺ - 2.92, Na⁺ - 4.83, SO₄^2- - 16.23, Cl^- - 21.20, Ca²⁺ - 8.02, Fe²⁺ - ­0.55 in the form of Fe EDTA, and microelements - 1 ml of Heller solution, and also C of organic matter - 5000 microg. Initial pH 6.5, the changes not exceeding ± 0.3 at the end of experiments. The experiment was repeated three times with 10 plants in a crystallizer as a sample. The medium was protected against evaporation by a synthetic film (Parafilm), permeable for gases. Medium temperature was 18°C, at diffuse day light. When changing the concentrations of factors examined, other remained at a level resembling the basic medium. The experiment terminated when the plant growth showed signs of regression.

As the results of experiment A were not explicit, the effect of ammonia, nitrates and phosphorus was examined again (experiment B) between June 18 and July 14, 1984. For faster and longer time of plant growth a germinant rhizome of Carex rostrata was placed in each crystallizer. Other factors were the same as in part A of the experiment.

E x p e r i m e n t  2. Conducted between June 6 and September 9, 1980, it aimed at determining the ecological optimum of A. vesiculosa in relation to water pH. In each aquarium with unfiltered water from natural habitat and rhizomes of Typha latifolia, 5 Aldrovanda plants were placed. Water acidity (pH) was adjusted by 2.5 n NaOH and 2 n HCl within 2.5-3.5, 3.5-4.5, 4.5-5.5, 5.5-6.5, 6.5-7.5, 7.5-8.5, 8.5-9.5. Because of insufficient plant material there were only two replicas of the experiment.

2.6. STATISTICAL AND MATHEMATICAL METHODS

The statistical methods used in elaborating the material were: analysis of variance, two-variable and multiple correlation. Analysis of variance with two factors according to the constant model (E 1 a n d t 1964) was used to estimate the variability of microhabitats and A. vesiculosa populations, the least significant difference (LSD) and also for testing the results of experiments. Tables with characteristics of microhabitats, habitats and populations give the importance of variance differentiation (IVD) determined by F-Snedocor test at probability level 0.05 (*), 0.01 (**) and 0.001 (***). For comparison of F values statistical tables were used (Z i e 1 i ń s k i 1972). Statistical size indices, allowing to arrange habitats and A. vesiculosa populations (Fig. 2), were calculated by means of standard characters. Two-variable and multiple correlations between particular plant and habitat characters were calculated in biologically justified cases. R a o (1965) described methods for determining coeffi­cients of two-variable and multiple correlations and for testing the significance.

Fig. 2. Statistical quantities - classification according to standard characters. a - classification of habitats acc. to total chemistry of water, b - Aldrovanda vesiculosa population arranged acc. to individual and group characters, c - A. vesiculosa population arranged acc. to nutrient content in plants.

RESULTS

DESCRIPTION OF HABITATS WITH CONSIDERATION TO COENOTIC RELATIONS

The habitat of population examined is:

(1) The southern part of overgrown pond formed by impounding the Proszkówka river at Nowa Kuźnia near Opole.

(2) North-western coastal waters of the mid-forest, dystrophic Lake Długie of Łęczna-Włodawa Lake District.

(3) North-eastern coastal waters on peat of the dystrophic lake Brzeziczno (Łęczna-Włodawa Lake District), where as in Lake Długie the bottom is covered by a thick layer of organic silt and is poorly overgrown by plants.

(4) Depression with water in a turf cover on one of the turning into peat bays of Lake Krzywe in the Augustowska Forest (at the outlet of Augustowski Channel to Lake Miklaszewo).

(5) Meander of the channel between Lake Krzywe and Kruglak.

(6) Eastern coastal zone adjoining a large community of the class Scheuchzerio-Caricetea fuscae of the dystrophic Lake Kruglak.

(7) Eastern coastal waters of eutrophic Lake Miklaszówek near the outlet of Augustowski Channel turning into peat but with dense vegetation.

(8) Small bay on Lake Krzywe close to the lock on Augustowski Channel.

(9) Small pool on a turning into peat valley of watercourse joining Lake Budziszewskie with Lake Powidzkie (some 200 m from the shores of the latter) of the Gniezno Lake District.

(10) Pool on the turning into peat northern shore of the dystrophic Lake Salomonowskie of the Gniezno Lake District.

The common thing for all these habitats are shallow eutrophic and dystrophic lakes, especially peaty, shallow (1 m deep), sheltered from wind and well heating coastal parts of these lakes. The bottom is covered by a thick layer of mineral-organic or organic silt. Underwater vegetation is much differentiated there, i.e., from very poor (localities 2, 3, 6) to abundant (locality 7). Usually A. vesiculosa grows in a narrow belt of nympheides and sedge rushes (sporadically in bulrushes) adjoining the forming communities of the class Scheuchzerio-Caricetea fuscae. It occurs less frequently in depressions of the moss-sedge turf overgrowing the lake. The analysis of phytosociological records (Table 1) shows that Aldrovanda occurs in different floristic associations, thus having a broad phytosociological amplitude. Usually its occurrence within one habitat has a mosaic character. In habitats examined it is a component of plant communities belonging to two phytosociological classes - Potamogetonetea and Phragmitetea - where it grows better. Among plant associations, especially those from the alliance Magnocaricion, it has the highest frequency and density. A. vesiculosa is most frequently accompanied by Hydrocharis morsus-ranae, Stratiotes aloides, various species of Carex, Typha latifolia and Utricularia vulgaris.

Table 1. Plant aggregates with Aldrovanda vesiculosa (see Table 1 on separate page)

3.2. CHEMISTRY OF WATER AND BOTTOM SEDIMENTS

Table 2 gives chemical characteristics of water of Aldrovanda habitats examined in 1980, which allowed to present statistically the size of habitats from the point of total water chemistry (Fig. 2) dividing them into extreme habitats (4, 10), intermediate habitats (6, 7) for further investigations.

Water from habitats examined was slightly acid (pH from 5.57 on locality 3 to 6.8 on locality 6) and soft. The water abundance in food components was determined according to   P a t a 1 a s (1960a, 1960b) system. Aldrovanda occurs in habitats most resembling the lakes from the first group in this classification, i.e., shallow ones without permanent thermal stratification in summer. Thus the water of habitats examined with the exception of the first locality had low nitrate content (0.10-0.37 mg.l^-1). Ammonium nitrogen content was high on the average and significantly differentiated. It was the lowest (0.5 - 1.03 mg.l^-1) in habitats with flowing water (5, 6, 8) and the highest (3.08 mg.l^-1), where organic substance accumulation was faster than its mineralization, i.e., on localities 3, 7, 9, 10, or when there was a possibility of runoff of ammonium salts from fields and of liquid manure from neighbouring farm buildings (localities 1, 9, 10). Generally, the habitats do not differ as to phosphate content in water, which during the period of greatest development of aquatic vegetation was high, on the average 0.03-0.085 mg.l^-1. The majority of habitats, except habitats 1 and 10, did not differ as to potassium content in water. They were averagely abundant in this element (1.23 - 7.30 mg.l^-1). Habitats with the highest concentration of ammonium nitrogen in water (1, 7, 10) were the most abundant in potassium. But in the habitats examined the contents of calcium were low in habitat 3 (7.77 mg.l^-1), averagely low in habitats 1 and 2, average in habitats 4, 5, 6, 7, 8 and high in habitats 9 and 10 (85.6 mg.l^-1); of iron - were the lowest in habitats 6 and 8 (0.05 mg.l^-1) and the highest in habitat 1 (1.44 mg.l^-1), and of chlorides were also differentiated. Magnesium content was relatively low, from 1.73 mg.l^-1 in habitat 1 to 15.03 mg.l^-1 in habitat 10. Its low content in relation to calcium indicates poor mineralization in these habitats (G o m ó ł k a and S z y p o w s k i  1975). The sodium content was also low and less differentiated, from 3.6 mg.l^-1 in habitat 4 to 16.2 mg.l^-1 in habitat 10. The sulphate content was also low and not much differentiated, being close to the average in the majority of habitats, i.e., 21.52 mg.l^-1.

Table 2. Characteristics of habitats of Aldrovanda vesiculosa populations