Grazing by microfauna and productivity of heterocystous nitrogen-fixing blue-green algae in desert soils [Protozoa, Nematoda, Anabaena, Nostoc]
1980
Ghabbour, S.I. | El-Ayouty, Y. (Cairo Univ. (Egypt)) | Khadr, M.S. | El-Tonsi, A.-M.S.
The presence of microfauna (Protozoa, Nematoda, etc.) in cultures of heterocystous nitrogen-fixing blue-green algae (Anabaena and Nostoc spp.) resulted in reduction of chlorophyll a content from 20.4 to 6.2 mg m('-2) and of organic carbon from 203.3 to 136.0 mg/100 g dry soil. However, total nitrogen content (fixed by the algae) was virtually unchanged (23.0 against 23.1 mg/100 g dry soil), and also NH(,4-)N (1.6 against 1.8/100 g dry soil). These values are the amounts gained in the soil after one month of incubating the organisms in sterilized desert soil from which they were originally isolated selectively. Soils were from two desert sites west of Alexandria, Egypt. Incubation was under continuous 5000 lux, at 30 and 37 deg C, and at 75, 100 and 150% W.H.C. The gain in total N and NH(,4)-N is superior to those of the treatments: (a) microfauna added to the algal culture 10 d after start - and: (b) microfauna added to soil without algae. Since it is known that Protozoa (which were predominant) do not affect heterocysts, Protozoa may stimulate nitrogen fixation, while reducing chlorophyll a and carbon fixation by grazing on the vegetative cells.
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