Propagation, taxonomy and ecophysiological characteristics of the Azolla-Anabaena symbiosis in freshwater habitats of Beni-Suef Governorate (Egypt).

Abstract

A new ecotype of Azolla fern has established in freshwater habitats at Beni-Suef Governorate. The fern propagates in shallow irrigation canals and drains with low-velocity water. Azolla fern is circular (fan-like) in shape with a diameter of 2-3 cm; the surface of the fronds is covered with trichomes and contains stomata with annular guard cells and central pores. Azolla is a sterile hybrid, only forming microsporocarps, never megasporocarps: the microsporocarp contains about 64 microsporangia. Each microsporangium consists of 4 massula, each characterized by the presence of anchor-like multiseptate glochidia covering the whole surface of the massula. This ecotype probably belongs to Azolla caroliniana on the basis of vegetative and reproductive characteristics. Growth (biomass yield) is seasonal, with higher biomass (3.0-4.5 kg m-2) and shorter doubling time in summer, reducing to about 1.0-1.5 kg m-2 in winter. Azolla plants accumulated the minerals Fe, Zn, Cu, Ni and Pb when growing in freshwater canals, drains and waste water. Salt stress treatment inhibited growth, nitrogen fixation and protein content. Iinhibitory levels of salinity were about 0.6-0.8 % NaCl. Growth and nitrogen fixation were inhibited at higher levels (2.4 mol m-3 and 5.1 mol m-3) of combined nitrogen (ammonium sulphate and urea). The ecophysiological significance of Azolla in the freshwater habitats of Beni-Suef Governorate is discussed.