CONTENTS-
Abstract
Introduction
Material and Methods
Results and Discussion
Acknowledgements
References

Lake ecosystems exist in many alternative states with respect to their species composition and ecosystem functioning for providing free services and goods. Each state of smaller shift is stable for short-term but greater shifts change the ecosystem from one state to another. Such state shifts are important to record the ecosystem health and for ecorestoration. Thresholds in the relationship between phytodiversity and ecosystem functioning are hypothetical but plausible. In lake Chilika, high phytodiversity during the winter increases the ecophysiological process rate and low phytodiversity during the summer decreases the ecophysiological process rate. Aquatic plant threshold values and curves are determined to record the Chilika lake ecosystem behaviour. It is observed that to restore the Chilika ecosystem,   the phytodiversity must be raised above the threshold value of upper range and not the lower range. The values   have significant implications for bioresource recovery, ecosystem restoration and sustainability of ecosystem services. Adaptive management techniques for detection and avoidance of thresholds and the desirable state for long-term stability of the aquatic ecosystem are needed to ecorestore the lake Chilika.

Lakes   are the most natural productive ecosystems of the world. Plants   play a key role   in   biomonitoring   the state of an ecosystem. A method for characterizing   the quality   of water by using plant systems   is reported by several workers (Wang, 1985; Biney, 1991; Misra Behera, 1991 and Das and Behera, 1993). When phytodiversity density rises above a threshold, the physiological values change rapidly and low productivity of the ecosystem indicates a state of degradation. In order to detect the ecodegradation of the lake Chilika ecosystem, the present investigation was carried out to detect the physiological threshold values of the dominant aquatic plants for phytomonitoring the lake ecosystem.

          Potamogeton pectinatus and Hydrilla verticillata, two dominant aquatic plants in the lake Chilika were selected as the plant systems. The plants were cultured in the three different water sources (river, lake and sea) for physiological tests. Nitrate and phosphate uptake were measured spectrophotometrically by the phenoldisulphonic method at 410 nm and the stannous chloride method at 690 nm respectively (Behera, 1986).

          The plants were grown in three different qualities of water for a period of   four weeks and the physiological parameters were analysed. The results on the growth of Patamogeton and Hydrilla species are expressed in R- values which is the ratio of the percentage weight increase of the test sample to that of the river water as control following the method of Biney (1991). Catalase was measured by the method of Machly and Chance (1967). Leaf samples, 100g each, were homogenised in cold 0.1 M sodium phosphate buffer, pH 7 and centrifuged at 4 0 C for a minute at 10,000 g. An aliquot of 1ml of the supernatant of the enzyme extract was added to the reaction mixture containing 1ml of 0.01 M hydrogen peroxide and 3ml of 0.1 sodium phosphate buffer, pH 7. The reaction was stopped after an incubation of 1min at 20 0 C by adding 10 ml of 1% H 2 SO 4 . The acidified medium without or with the enzyme extract was titrated against 0.005 N KMnO 4 and catalase activity was expressed as milli moles of hydrogen peroxide utilised per gram leaf fresh weight per minute. Each value represents the mean of five replicates.

          Table I summaries the results for the observation on growth of Potamogeton and Hydrilla species and has been expressed as percentage weight decreased as R- values. Wang (1985), Misra and Behera (1991) and Das and Behera (1993) showed that pH range did not have a significant effect on the plant system but the present investigation showed a significant effect on the two aquatic plant systems. The R-values   increased with increased salt concentration of the test solution.

Table I. Effect of different qualities of water on growth of Potamogeton and Hydrilla

Table II. Nitrate uptake by Potamogeton in relation to different qualities of water and time.

Table III. Nitrate uptake by Hydrilla verticillata in relation to different qualities of water and time.

Table IV. Phosphate uptake by Potamogeton pectinatus in relation to different qualities of water and time.

Table V. Phosphate uptake by Hydrilla verticillata relation to different qualities OF water and time.

Table VI. Catalase activity in leaves of Potamogeton pectinatus at different time exposer to various water quality.

A gradual decline with the time of exposure   to quality of water and   salt concentration, the biomass yield   is correlated   to the loss of nutrient uptake and enzyme activity of the two plant systems studied. Potamogeton pectinatus seems   to be more adaptable to salt stress in comparison   to Hydrilla verticillata      (Table II – VII). Our data on the uptake of nitrate and phosphate nutrient and growth of Potamogeton and Hydrilla suggest that the Chilika lake water has greater adaptation at prolonged exposure   and could lead to increased physiological threshold values.

At present, a firm conclusion cannot be drawn in these pilot experiments regarding the physiological threshold values in aquatic ecosystem on the adaptation and phytomonitoring of lake Chilika. However, the results suggest that in an evaluation of phytodiversity and ecosystem stability of the lake Chilika, the nutrient uptake and enzyme activity rate beyond the physiological threshold value, can act as physiological indicators at a particular time of exposure to the quality of aquatic ecosystem.

The authors thank Head of the Dept. of Botany for extending necessary departmental facilities.   The award of research fellowship by the Department of Ocean Development (DOD), New Delhi to N. Lata is acknowledged. This investigation was supported by a grant awarded to PKB by the DOD, Govt. of India, New Delhi and the Ocean Science and Technology Cell (OSTC), Berhampur University.

Behera, B. K and Misra, B.N. 1982, Analysis of the effect of industrial effluent on growth and development of rice seedlings. Environ Res. , 28, 10-20.

Behera, P.K. 1986. Influence of photoperiod and mineral nutrients on the biorhythmic activities of sunflower root systems.   Ph.D thesis. Moscow Agri.Academy, Moscow, Russia.  

Biney, C.A 1991, A method for characterized natural and waste waters using plant seeds. Environmental monitoring and Assessment 18 : 123-128,00.

Das, M. 2002.Ecotechonological and Biotechonological aspects of flowering in screwpine ( Pandanus fascicularis Lam.) Ph.D thesis, Berhampur University, p.1-132.

Das, S.S. and Behera, P.K : 1993 , Physiological effects of sunflower crops grown in paper mill effluents Poll Rs. 12(2) : 97-100.

Machly, A.C. and Chance, B (1967). Methods of biochemical analysis. Vol. 1, (ed D. Glick), Interscience publishers Inc., New York, 357-424.

Mishra, R.N and Behera, P.K., 1991. The effect of paper industry effluent or growth pigments, carbohydrate and proteins of rice seedlings, Environ. Pollut 72. 159-167.

Patra, P.K. 2002. Ecotechonological   and Biotechonological aspects of growth and propagation   of screwpine
( Pandanus fascicularis ). Ph.D thesis, Berhampur University, p.1-126.

Wang, W .1985, The use of plant seeds in Toxicity Tests of Phenotic compounds Environ Int. 11, 49-55.

Plant Physiology and Biochemistry Laboratory,
P.G. Department of Botany,
Berhampur University,
Berhampur-760007, Orissa, India.
E-mail: pcac-b@yohoo.com