|
|
|
AZOLLA PINNATA R.Br. PTERIDOPHYTE; SALVINIALES (AZOLLA CEAE) IN THE MANAGEMENT OF LAKE AGRO ECOSYSTEM - G.V. Gopal
|
|
|
|
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS AND DISCUSSION
ACKNOWLEDGEMENT
REFERENCES
| ABSTRACT: |
|
The data obtained on the morphology of the water fern Azolla pinnata R.Br. in different seasons from the Kukkarahalli lake of Manasagangotri, University of Mysore campus, was compared with the published morphological accounts on the plant. Humidity (85-95% RH), temperature (20-40°C) and pH (5-5.7) were found to influence the luxurious growth of the plant. The management and usage of this plant in a lake agro-ecosystem for better production of fertiliser, increase in efficiency and productivity, aquaculture, nitrogen fixation, food for poultry, use as antifungal agent and water purifier, has been highlighted here.
| INTRODUCTION: |
|
The water ferns, viz. Azolla pinnata, A. microphylla and A. filiculoides are the common pteridophyte species found in Kukkarahalli lake, of which the latter two are common in the lake, while A. pinnata R.Br. is the most dominant ubiquitous occurring in roadside ponds, pools, lakes and other standing waters. The plants cover the entire surface of the water body, the young plants having green or bluish green leaves, which turn red on maturity, and are easily recognised from a distance.
Azolla as an atmospheric N2 fixer, water purifier, poultry feed, antifungal agent, bio-fertiliser and producer of hydrogen gas is well documented by various researchers: Galston (1975); Gopal (1967); Kasmi and Trivedi (1978); Mandal and Ghosh (1990); Newton (1976); Saunders and Flower (1992); Singh (1977); Singh and Subudhi (1977); Subudhi and Singh (1978b); Surange (1966); Watanabe (1978).
This water fern is represented by as many as six species distributed throughout the world under two sections: Azolla and Rhizosperma. Azolla is characterised by hooked massulae or anchor shaped glochidia. Megaspore apparatus has three floats in the swimming apparatus. A. Caroliniana auct nonwilld., A. filiculoides Lam., A. microphylla auct. Non-Kaulf and A. mexicana perst are included in this section. Rhizosperma has massulae either with straight, simple or branched glochidia or without them; megaspore apparatus has nine floats of unequal sizes. This section includes A. nilotica, Occne ex Mett. and A. pinnata R.Br.
Saunders and Flower (1992) divided A. pinnata R.Br. into three subspecies viz. A. pinnata ssp pinnata, A. pinnata ssp asiatica and A. pinnata ssp africana Oesv; of which only A. pinnata ssp. asiatica occurs in India. Besides India, this subspecies also occurs in Japan, China, Myanmar and South East Asia.
| MATERIALS AND METHODS |
|
The Azolla species was collected in different seasons (see Fig.A) for close and distant view from Kukkarahalli lake, near the Mysore University Crawford Hall administrative building. The collected plants were grown in artificial water tanks at the green house of RIE, Mysore. The plant was collected during June-July, November-December and April-May, to study the various stages of development of its body. The pH and temperature of the surface waters were recorded directly in the field.
| RESULTS AND DISCUSSION |
|
Azolla plants have crowded mass like leaves borne on a fragile free-floating rhizome with submerged roots (Fig.A & B). The leaves are arranged in alternate rows and each leaf is divided into two lobes of which the upper lobe is areal and lower lobe is submerged in water. The areal lobe is more than one cell thick and is photosynthetic in nature with stomata on both surfaces. The upper epidermis of the lobe has one or two celled hairs (Fig. C & D) and the lower surface of the lobe has mucilaginous cavities harbouring live colonies of Anabaena azollae strasb (Fig.D) showing a symbiotic relationship between the alga and plant (Vasishta 1982). The submerged lobe is one cell thick only. Branching is free and occurs at the nodes. The roots are borne on the lower side, close to the point of origin of branches.
The most interesting feature is symbiotic association of blue green alga namely Anabaena azollae strasb (Cyanophyceae) with the Azolla species. This alga lives endophytically in the inter-cellular spaces of basal leaves of Azolla (Fig.D). Due to the presence of heterocyst in the algal cell the atmospheric nitrogen is fixed and transferred to the Azolla leaf in the form of ammonia. A. pinnata R.Br. ssp. asiatica grows floating in the fresh water lakes, ponds, ditches, streams and paddy fields in India. The large-scale growth has been experimented by Gopal (1967). It was shown that during growing season it could grow double its weight in less than seven days.
The pH (5 to 5.7), temperature (20-40°C) and relative humidity RH (85-95%) are observed to influence the growth of Azolla. These observations are in agreement with those reported by Roy and Banerjee (1998). Azolla is a wetland plant and prefers humidity of 85-90% RH (relative humidity) for its growth and development. Azolla grows very fast and below 60% humidity dries up. High light intensity inhibits its growth, and the plant turns red from green. It has been observed that Azolla plant remains green when kept in a shaded area, but turns red in the open scorching sunlight. Watanabe (1978) from Japan reported that in low land paddy field experiencing 5k, 10k and 40k lax light intensity the growth of Azolla is optimum.
Azolla can tolerate and survive within 14 - 40°C water temperature, but 20-30°C temperature helps its high growth. Azolla was reported to attain maximum growth during September to January and decline during April to June due to high temperature (Watanabe 1978). But in Kukkarahalli lake the fern is prolific up to March and the growth subsequently reduced. The plant grows rapidly at pH 5-5.7.
A perusal of the published accounts on Azolla reveals that it is a multifaceted and multipurpose bio-resource (Singh and Subudhi, 1977, 1978; Singh, 1977). It can be used as:
Azolla is used in lake-agro ecosystem in inland fisheries and aquaculture, where water quality management is mandatory for prevention of water pollution and harvesting optimum production. Appropriate technologies for water treatment without impairing the water quality need to be adopted. This is to ensure the health, hygiene and environmental sanitation of the aquatic ecosystem and prevent disease transmission to man through edible aquatic organisms.
A variety of vector insects capable of transmitting a host of diseases to mankind inhabit polluted aquatic systems. These affect the efficiency and productivity of lake-agro ecosystems; further the precious inland water resources are rendered an unusable burden. The high organic loads associated with high BOD and COD results in eutrophication and render the water unsuitable for human and agricultural use. Azolla is a natural biophysical scavenger that absorbs and depletes the organic nutrient load of the eutrophic lake agro ecosystems rendering them oligotrophic and rejuvenated.
Thus, in the lake agro ecosystem management, Azolla is useful in controlling eutrophication, maintenance of water quality and conservation of biological diversity. In addition, Azolla as already stated, is a powerful bio-agent capable of fixing atmospheric N2 and releasing H2. The biomass of the plant is useful for biogas production, as organic manure, poultry feed, and antifungal agent. As such, Azolla is not a bane but a boon if proper ecosystem management methods and ecofriendly technologies are used for sustainable development of the agro-lake ecosystems benefiting mankind.
| ACKNOWLEDGEMENT: |
|
Thanks are due to Prof. A.L.N. Sharma, Head, DESM for his constructive criticism, Dr. V.V. Anand, Head, Botany Section for manifold help, last but not the least to the Principal, RIE, Mysore for his constant co-operation and encouragement.
| REFERENCES |
|
| Address: |
|
Department of Botany,
DESM,
Regional Institute of Education (NCERT),
Mysore 570 006,
Karnataka,
India
|
|
|