OCCURRENCE OF CHROOCOCCACEAE DURING RICE CULTIVATION IN NORTH BIHAR , INDIA

The species richness of cyanobacteria belonging to the family Chroococcaceae in rice fields of North Bihar, India was studied over a 60-day period. Twenty-eight species representing nine genera were identified. The highest number of 21 species was observed around 30 day against eight and 13 species around 10 and 60 day of rice cultivation, respectively. Aphanocapsa grevillei (Hass.) Rabenh., Aphanothece naegelii Wartm and Microcystis marginata (Menegh.) Kützing were observed from 10 to 60 days of rice cultivation. Introduction Cyanobacteria are geographically widespread in freshwater, marine and terrestrial habitats. Some genera are capable of nitrogen fixation and are therefore of great importance for the balance in ecosystems. With the establishment of agronomic potential of cyanobacteria (De, 1939), the distribution of cyanobacteria and their role in maintaining soil fertility has variously been studied throughout the world (Begum et al., 1993, 1996, 2008; Khan et al., 1994; Singh et al., 2001). Cyanobacteria have been reported to promote the nitrogen economy of the soil by converting atmospheric nitrogen into soluble form of ammonia with the help of enzyme nitrogenase complex contained within the specialized structure heterocyst (Ernst et al., 1992). Additionally, cyanobacteria contribute phosphorus to the soil by mobilizing the insoluble phosphate present in the soil with enzyme phosphatases (Mishra et al., 2005). Moreover, cyanobacteria enhance the water holding capacity by adding polysaccharidic materials to the soil (Choudhary et al., 2007) and increase the soil aggregation property. Cyanobacteria have also been reported to excrete growth promoting substances into the soil (Gupta and Shukla, 1969). Rice is one of the main crops of Bihar and is cultivated in most part of the state. Rice fields favour the growth of cyanobacteria in terms of light, temperature, pH, humidity, water and nutrient availability (Mitra, 1951). Heterocystous forms of cyanobacteria have been extensively studied for their diversity in rice fields (Singh, 1961; Choudhary, 1999). The information on systematic enumeration of non-nitrogen-fixing forms including Chroococcaceae in the rice fields is limited. This study has been aimed to enumerate the periodic occurrence of Chroococcaceae in some rice fields of North Bihar, India. 1 E-mail: kkc1970@gmail.com


Introduction
Cyanobacteria are geographically widespread in freshwater, marine and terrestrial habitats.Some genera are capable of nitrogen fixation and are therefore of great importance for the balance in ecosystems.With the establishment of agronomic potential of cyanobacteria (De, 1939), the distribution of cyanobacteria and their role in maintaining soil fertility has variously been studied throughout the world (Begum et al., 1993(Begum et al., , 1996(Begum et al., , 2008;;Khan et al., 1994;Singh et al., 2001).Cyanobacteria have been reported to promote the nitrogen economy of the soil by converting atmospheric nitrogen into soluble form of ammonia with the help of enzyme nitrogenase complex contained within the specialized structure heterocyst (Ernst et al., 1992).Additionally, cyanobacteria contribute phosphorus to the soil by mobilizing the insoluble phosphate present in the soil with enzyme phosphatases (Mishra et al., 2005).Moreover, cyanobacteria enhance the water holding capacity by adding polysaccharidic materials to the soil (Choudhary et al., 2007) and increase the soil aggregation property.Cyanobacteria have also been reported to excrete growth promoting substances into the soil (Gupta and Shukla, 1969).
Rice is one of the main crops of Bihar and is cultivated in most part of the state.Rice fields favour the growth of cyanobacteria in terms of light, temperature, pH, humidity, water and nutrient availability (Mitra, 1951).Heterocystous forms of cyanobacteria have been extensively studied for their diversity in rice fields (Singh, 1961;Choudhary, 1999).The information on systematic enumeration of non-nitrogen-fixing forms including Chroococcaceae in the rice fields is limited.This study has been aimed to enumerate the periodic occurrence of Chroococcaceae in some rice fields of North Bihar, India.

Materials and Methods
The study was conducted in some rice fields of Muzaffarpur district (latitude 26°7'12"N and longitude 85°24'0"E) of North Bihar.Cyanobacterial occurrence in rice fields has been documented in terms of cultivation cycle.The cyanobacterial diversity was enumerated randomly around 10 th , 30 th and 60 th days of plantation of rice seedlings in rice fields.
Cyanobacterial samples growing in heterogeneous assemblage were randomly collected from upland and lowland rice fields representing the terrestrial as well as freefloating masses.The samples were collected in culture tube (50 ml) and brought to the laboratory.The taxonomic enumeration was performed with fresh materials in the laboratory.The taxa were identified with the help of Desikachary (1959).

Results and Discussion
The study revealed 28 species belonging to nine genera of Chroococcaceae described below.Cells spherical, single or two together, 4.5-5.5 µm in diameter, pale-green in colour.
The enumeration of cyanobacteria revealed the maximum diversity during the midcultivation cycle of the rice fields (Table 1).The study showed maximum 21 species around 30 th day of rice plantation followed by around 60 th day (13 species) and minimum around 10 th days (8 species).The occurrence of lesser number of forms during early cultivation stage might be attributed to the inhibitory effect of high light intensity, whereas fewer forms in the later part might be due to loss of nutrients as well as low light intensity reaching to the surface due to increased rice canopy.This was in agreement of the cyanobacterial distribution reported by Gupta (1966).The poor distribution of cyanobacteria in high light intensity suggested them to be sensitive to high light intensity and as low-light species (Roger and Reynaud, 1979;Choudhary, 2009).Synechocystis pevalekii -R - The proliferation of non-nitrogen-fixing members of Chroococcaceae during midcultivation cycle might further be attributed to the availability of sufficient nitrogen along with other nutrients in the rice fields with suitable light intensity.Singh (1978) also reported the development of non-nitrogen-fixing forms in rice fields.He further described the early appearance of nitrogen-fixing forms in unfertilized plots than fertilized ones.It might be proposed that the appearance of non-nitrogen-fixing forms in rice fields might play an important role in establishment of nitrogen fixers by reducing the nitrogen status of the field by utilizing nutrients, particularly nitrogen.In this way, non-nitrogen fixers play a significant role in nutrient cycling and development of other biological system to fill up the gap produced in terms of nutrients.
Finally, it might be concluded that the documentation on cyanobacteria may enhance the understanding of the nutrient status of the field and might be applied for sustainable agricultural practices by reducing the application of chemical fertilizer to avoid the appearance of non-nitrogen fixers in the soil that might compete with nitrogen fixers for nutrients (Agawin et al., 2007).