Ann. Bot. 47, 31-52, 1981 Multivariate Interpretation of the Distribution of Nitrogen-fixing Blue-green Algae in Rice Soils in Central Sri Lanka S. A. KULASOORIYA and R. S. Y. de SILVA Department of Botany, University ofPeradeniya, Peradeniya, Sri Lanka Accepted: 26 April 1980 ABSTRACT The ecology of nitrogen fixing blue-green algae in ricefieldsof Central Sri Lanka was studied using multi- variate techniques of analyses. In this study 73 strains of heterocystous blue-green algae, belonging to 21 genera were isolated and the distribution of the 46 most abundant strains was examined in relation to ecological parameters. Besides pedological factors such as pH, water holding capacity and available phosphorus; environ- mental factors including rainfall and altitude have shown up as parameters influencing the distribution of the algal species. On the other hand, soil organic carbon, total nitrogen, potassium and calcium, do not appear to play an important role in determining the composition of the algal flora. While certain algal species were ubiquitous in their distribution some were restricted, and a few even showed a tolerance to stands with low soil pH and low levels of phosphorus. The agronomic potential of such species is of value especially in relation to rice-growing soils of this District, where low pH and low levels of phosphorus are major limiting factors for the profuse growth of blue-green algae. Key words: Blue-green algae, nitrogen fixation, Sri Lanka, rice-growing soils, multivariate analysis. INTRODUCTION The role of blue-green algae in the nitrogen fertility of paddy soils have been convincingly established (Singh, 1961; Watanabe, 1962, 1966, 1973; Sahay, 1966; Watanabe and Yamamoto, 1971) and it is generally accepted that they can be used to supplement mineral fertilization (Venkataraman, 1972). Most of the investigations on blue-green algae in Sri Lanka, have been taxonomic, rather than ecological or agronomic (West and West, 1902; Fritsch, 1907; Holsinger, 1935; Chandraratne, 1957; Thirukkanasan, Kulasooriya and Theivendirarajah, 1977; see also Desikachary, 1959; Durairatnam and Amaratunga, 1969), and very little information is available regarding their importance on the fertility of paddy soils (Chandraratne, 1957; Kulasooriya and de Silva, 1978). A series of investigations has therefore, been undertaken to explore the biology and agronomic potential of blue-green algae in Sri Lanka, and as a first step, the results of a comprehen- sive survey of the blue-green algal flora in rice soils will be reported here. Little is definitely known about the ecology of blue-green algae in rice soils, (Watanabe and App 1979) and only a few reports have dealt with this aspect (Matsuguchi, Tangcham and Patiyuth, 1975; Roger and Reynaud, 1979; Stewart, Rowell, Ladha and Sampaio, 1979). In the present paper an attempt has been made to examine the ecology of blue-green algae in rice soils in central Sri Lanka using some of the modern multivariate techniques. Although, these techniques have increasingly been employed to analyse data from higher plant communities (Greig-Smith, 1964; Kershaw, 1975), they have been applied very rarely in algal ecology (Allen, 1971). 0305-7364/81/001031+22 $02.00/0 (£• 1981 Annals of Botany Company by guest on February 7, 2011 aob.oxfordjournals.org Downloaded from