Development of algae on artificial substrates used for plant cultivation

LUBOMIRA BURCHARDT¹ and EWA DANKOWSKA²

¹ Department of Hydrobiology, Adam Mickiewicz University, Marceliñska 4, 60.801 Poznañ, Poland
² Department of Plant Protection Methods, Agricultural University, Zgorzelecka 4, 60.198 Poznañ, Poland

Abstract: Development of algae on polyurethane and Flormin rockwool substrates used for tomato and gerbera culture, was observed during series of phycological readings. In all cultures, the same type of nutrient solution was applied. Simultaneous observations of algal succession revealed differences in developmental trends of algae between tomato and gerbera cultures and between the two substrates in tomato cultures.

Key words: succession, green algae, hydroponic culture, biodiversity

INTRODUCTION

Recently there has been a growing tendency to abandon traditional substrates for plant cultivation (like earth, leaf mould or peat) and to replace them with some artificial substrates (like polyurethane, rockwool or perlite). Artificial substrates do not enter into reaction with nutrients. They also do not show any chemical sorption because they do not have any sorption complex. On the other hand, they create op­timal air and water conditions for root systems of plants. In such substrates, fertiga­tion (i.e. fertilisation combined with irrigation) takes place through droppers supply­ing a nutrient solution to each plant individually.

During cultivation of tomato and gerbera on artificial substrates, a gradually developing bloom was observed on the surface of the substrate. Algological identi­fication revealed the presence of green algae (Chlorophyta). Further phycological observations carried out during the growth of the plants (tomato, gerbera) showed qualitative differences. Differences in the structure of algal communities developing on various substrates were reported earlier by YOUNG (1945), SLADECKOVA (1963), FOERSTER & SCHLICHTING (1965), BACKHAUS (1967), TIPPET (1970), SCHLICHTING (1974), NIELSEN et al. (1984) and KAWECKA & ELORANTA (1994).

There are also some reports denying these suggestions and pointing to the presence of similarities in the development of algal communities on artificial and natural substrates (PATRICK et al. 1954, ODUM 1957, CASTENHOLZ 1960, PIECZYÑSKA & SPODNIEWSKA 1963, MILLIE & LOWE 1983, KAWECKA & ELORANTA 1994). Therefore the cultures were repeated in order to achieve a better understanding of the process in the course of time and to confirm the presumption that each type of substrate activates a different developmental trend of algae.

MATERIAL AND METHODS

Tomato and gerbera cultures were established by taking the following steps:

(1) preparation of blocks (10 cm × 10 cm × 7 cm) of polyurethane foam and of rock-wool (Flormin); (2) sowing of seeds into .seed sheaths. on 2nd April 1998; (3) soaking the blocks with the nutrient (without the sheaths); (4) transfer of the sheaths with plants into the blocks.

Phycological readings on the surface of each substrate were repeated several times till 29th April 1998, in two series for each plant species, according to the following procedure:

• the material for analyses was taken each time from the surface of 1 cm²;
• the algological material was washed out from the substrate with 10 ml of distilled water;
• observations were carried out on living material;
• in the final phase, the material was preserved with Lugol.s solution.

The following nutrient composition was used for plant cultivation on poly­urethane or Flormin rockwool: N-NO₃ - 260 mg/dm³, P - 62 mg/dm³, K - 260 mg/ dm³, Ca - 22 mg/dm³, Mg - 49 mg/dm³, S - 12 mg/dm³, Fe - 0.84 mg/dm³, Mn - 0.55 mg/dm³, Zn - 0.33 mg/dm³, B - 0.32 mg/dm³, Cu - 0.05 mg/dm³, Mo - 0.55 mg/dm³, pH - 5.5, EC (electrolytic conductivity) - 3.1.

RESULTS

In the two series of tomato culture, two qualitatively different trends of algal development were observed. In the first series, on polyurethane (Fig. 1), the devel­opmental cycle of one taxon only, Chlorococcum diplobionticum Herndon, was seen (Fig. 5). In the second series, on Flormin rockwool (Fig. 2), two taxa were distin­guished: Chlamydomonas lobata Pascher and Chlorococcum diplobionticum (Fig. 6). The former taxon appeared in the first period of the culture (3rd . 8th April 1998), and was succeeded by the latter species at the end of the culture (14th . 29th April 1998).

In the two cultivation series of gerbera on two types of substrate (Figs 3, 4), a constant development of one taxon, Chlorococcum oleofaciens Trainor et Bold, was observed (Fig. 7). In all phycological readings done between 3rd and 29th April 1998, only the different developmental phases of this taxon were found.

The phycological readings in cultures of both plants (tomato and gerbera) car­ried out on the 3rd, 8th and 14th April 1998, showed that the growth of algae was quicker on polyurethane foam than on Flormin rockwool.

Chlorococcum diplobionticum in the first four days (3rd . 7th April 1998) of the first series of tomato culture occurred as vegetative cells (Fig. 5). On the fifth day (8th April 1998), aplanospores and zoospores were observed. The zoospores occurred for six days (till 14th April 1998). Further culture (22nd . 29th April 1998) showed the occurrence of aplanospores only. The observations of the second series of tomato culture (Flormin rockwool, Fig. 6) showed the occurrence of this taxon as aplanospores between 12th and 29th April 1998, whereas vegetative forms appeared later (29th April 1998). On Flormin rockwool, the development of this taxon took place after the end of development of Chlamydomonas  lobata  Pascher, which was found there till 8th April 1998.

Morphology of all three forms of Chlorococcum diplobionticum  in two series was analogous to the description of this taxon showed by KOMAREK and FOTT (1983) from four water biotopes.

Chlamydomonas lobata Pascher (Fig. 6) occurred in the first part of the sec­ond series of tomato culture (3rd . 8th April 1998) as vegetative cells with a chlo­roplast, two flagella and a stigma (HUBER-PESTALOZZI 1961). This taxon was ob­served earlier in waters of the botanical garden in Prague (ETTL 1983).

Chlorococcum  oleofaciens Trainor et Bold (Fig. 7) developed intensively throughout the culture period (3rd . 29th April 1998) and produced at the same time vegetative cells, aplanospores and zoospores (without hypnospores). KOMAREK and FOTT (1983) recorded this taxon in various aquatic habitats.

CONCLUSIONS

The obtained results confirm the earlier suppositions and the earlier data refer­ring to the species diversity of algae on different substrates in spite of application of the same nutrient. Research on this subject should be supplemented in the future with a detailed chemical analysis of the substrate because it is possible that there are some root system reactions of the quickly growing vascular plants. There is also a possi­bility of occurrence of specific bacterial microfloras and of atmospheric changes altering in different ways the chemical properties of the substrate.

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