Abstract: E. crassipes and P. stratioites can be used as biological indicator in polluted aquatic habitats if the nature of the polluting salts from effluents is known, as both these plants showed selective responses to different salts. Low sodium salinity acted as growth promotor for both the plants. P. stratioites was more tolerant of HCO3 and Na+ but not NH4 NO3 and E. crassipes was sensitive to HCO3 but tolerant of NH4NO3 induced eutrophication.
Introduction
Growth suppression with increase in salt levels around rhizosphere is an established fact. Hanif and Daves (1998) reported a disturbance in apical dome of root meristem with increase in salt concentrations which ultimately interfered with growth of plants. While Ashraf and O'Leary (1997) studied a disturbed ionic relations at cellular and subcellular levels. These studies were mainly focused for the determination of the effects of salts on the growth of plants.
The idea of the use of biological indicators for the evaluation of pollution levels is very recent one. Schmedtje and Kohmann (1988) emphasized the importance of biological indicators for the study of pollution status of a water body on the grounds that chemical indicators can be applied on a limited and restricted scale while biological indicators respond to all the physical, chemical and biological factors and can safely be applied at broader scale for the evaluation of pollption in water reservoir. Danjun and Zujie (1987) emphasized on the use of Eichhornia crassipes as environmental regulator in polluted water reservoir according to these workers, water hyacinth reduced injurious factors in the vicinity of root zone at one hand and could be utilized as substitute fodder for milch and dairy animals on the other. This study will go a long way in the understanding of both the aquatic macrophytes as biological indicators and will pave the way for more complex studies in developing a model for pollution evaluation in aquatic habitats by using biological indicators.
Materials and Methods
Fifty six polyethylene lined ponds of 2ft x 2ft with uniform depth of 9 inches were made at the experiment site and were marked according to salt and treatment level. These ponds were filled with thirty five liters of solution. Each having a concentration level of 0, 100, 500 and 1000 ppm of either of the salts NaCI, NH4CI, Na2CO3, NaHCO3, CaO Cl2 and NH4NO3.
Eichhornia crassipes of uniform size and age were selected from a waste water body at Panjpulian near University of Agriculture, Faisalabad and Pistia stratioites from waste water body from Kamalpur, a suburb 11 km from Faisalabad. Thoroughly washed plants were immediately transferred to artificially constructed ponds at Botanical Gardens, University of Agriculture, Faisalabad.
Water level in the ponds was marked with indelible ink and water loss throughout the experiment was maintained by the addition of distilled water to the ponds. pH range of all the ponds was between 5.0-7.0 and maintained through out the experiment after following Nor and Cheng (1986). Fifteen days was taken as inter harvest period and five consecutive harvests were made by random sampling in triplicate from each pond. At each harvest after washing the whole plant parts, such as leaves, stems and roots were separately measured and weighted and were over dried for dry weight calculations. Following physical growth parameters were recorded.
| i. | Root fresh weight |
| ii. | Root dry weight |
| iii. | Shoot fresh weight |
| iv. | Shoot dry weight |
| v. | Leaf area |
Net assimilation rate (NAR), relative growth rate (RGR), leaf area ratio (LAR) and relative leaf expansion rate (RLER) were calculated using the formulae. The data obtained was subjected to minitab computer programme (Minitab,1989) and the comparison of means was made by using Duncan's multiple range test.
Results
Some correlations were established between relative growth rate and NAR. LAR and RLER under different salts in both the plant species (Table 1).
| Table 1: | Comparison of RGR correlation values with NAR, LAR and RLER of E. crassipes and P. stratioites |
Under control conditions RGR of Eichhornta crassipes was positively related to NAR, LAR and RLER. While in case of Pistia stratioites a negative correlation of RGR with LAR was found, whereas NAR and RLER indicated no relationship. RGR had no relationship with any of the growth parameters in case of E. crassipes exposed to various salts except for NH4NO3. Where it showed a non-significant correlation of RGR with NAR, LAR and RLER.
A positive correlation was observed between RGR and RLER of P. stratioites. E. crassipes indicated a positive correlation between RGR and rest of the parameters under NH4CI treatment but it was not recorded for Pistia. RGR of E. crassipes treated with NaHCO3 was negatively related to NAR. While LAR and RLER of E. crassipes was negatively related to NAR under Na2CO3 and Ca0Cl2, It was positive for P. stratioites for both the salts. However, RGR of E. crassipes was not related to NAR, LAR or RLER under NH4NO3 treatments. While in case of Pistia stratioites only LAR was negatively related to RCA.
Discussion
RGR values of both the plants and their correlations with other derived parameters i.e., LAR, NAR and RLER showed that E. crassipes is more tolerant of NaCI and NaHCO3. A differential response of NH4CI and NH4NO3 is visible between the two plant species. When exposed to salt shocks plants showed disturbance in cell size and number in meristematic regions, which resulted in a suppressed growth of plants (Hanif and Daves, 1998). Einor et al. (1989) reported the involvement of NH4 nitrogen source in the respiratory enzyme metabolism. Which may be the reason of this selective behaviour of NH4-nitrogen in both the plants. Ashraf and O'Leary (1995) reported a changed ionic patterns within plant when it was exposed to higher concentration of salts. However, these results demand further elaborated biochemical studies.
E. crassipes. and P. stratioites showed a differential response towards bicarbonates. Similar responses of plants has already been reported by Overpeck et al. (1990). All these reports indicated a tendency of growth suppression with increasing pollution.
DeBusk et al. (1986) emphasized to need of a plant cover to the water pools in vicinity of industrial plants. The plant cover acts as water treatment system. Due to higher carbon assimilator rates, E. crassipes and P. stratioites are able to produce huge quantities of organic matter per unit area, which can be utilized for the generation of energy. Furthermore, these plants may be used as biological indicators if the nature and source of pollutants is known.