Effects of Some Limnological Factors on the Growth of Nelumbo Nucifera Gaertn

Nelumbo nucifera Gaertner was grown in a mesoscale culture by sowing seeds in cow dung compost and loamy soil (1 : 1). Rhizomes and young plantlets under ex-situ condition did not survive but germination was possible via seeds where the rate of germination was 50% and seedlings less than four months old also grew. Leaf area positively correlated with air temperature, water temperature, PAR, day length, rainfall, relative humidity, NO3-N, Chl a and phaeopigment. Petiole length showed positive correlation with rainfall, relative humidity and pH. Highest growth and flowering were found to be associated with a water depth of 100 cm under full sunshine and high nutrient conditions. Under shaded condition, plants did not produce flowers. Water flow rate of 50 ml/sec in the culture pit hampered flowering. Flowering was observed only in the stagnant condition. Introduction Bangladesh has a wetland area of about 74,197 km (Akonda 1989), where about 100 species of Angiosperms, 3 species of Bryophytes and 8 species of Pteridophytes commonly occur (Khan and Halim 1987). All these species play an important role in the socio-cultural and economic activities of the people living in the catchments of the wetlands. Nelumbo nucifera Gaertner (locally called Padda) is an important wetland macrophyte species which grows naturally in different Haor ecosystems of greater Sylhet and Kishoreganj districts. The species has also been reported from some Beel ecosystems of Rajshahi district (Ahmed et al. 2009). Their harvest is fully dependent on natural population which is frequently damaged by other ongoing activities in the Haor such as fishing, boating, agriculture, etc. Considering the significance of the plant, Goel et al. (2001) made an ex-situ conservation strategy where a national collection comprising of 60 species/races of Nelumbo have been maintained in the National Botanical Research Institute, Lucknow (India) under the biodiversity conservation programme. In Bangladesh, very few works on macrophytic vegetation have been carried out and those are mainly taxonomic and a few ecological (Islam 1993, Khondker et al. 1993, 1994, 2004, Alfasane et al. 2010). Recently biochemical composition of the seeds of N. nucifera and Euryale ferox Salisb. were studied by Alfasane et al. (2008, 2009). There exists almost no research work in Bangladesh on the growth studies of N. nucifera. The present research has therefore been undertaken to carry out an ex-situ growth studies of N. nucifera and its relationship with some limnological factors. Materials and Methods The present research was carried out in the arboretum of Department of Botany, University of Dhaka between 2005 and 2007. Cut pieces of rhizome of Nelumbo nucifera Gaertner were collected from a ditch near the Botanical Garden of Chittagong University in April, 2005 and transplanted in the earthen bin filled with tap water in the Botanical Garden of Dhaka University. But the rhizomes did not survive. Thereafter (in July, 2005) five plantlets of 6 months old (20-30 cm in length) of N. nucifera were collected from the National Botanical Gardens, Mirpur, Dhaka. *Corresponding author.