Cyanobacteria in biological soil crusts of India

Species of filamentous, sheath-forming cyanobacteria were the major component in the blackish-brown crusts on the upper millimetre of soils in different regions of India. Chlorophyll a density of these biological crusts on lateritic soils of Bhubaneswar, Orissa, brown forest soils of Salbani, West Bengal, and soils of Tiruchirappalli, Tamil Nadu and sandy soils of old Goa ranged between 248 and 282 mg m(-2), which is of the same order as in the leaves of higher plants. The species composition of cyanobacterial community in these soil crusts of India has been documented. Organisms in the crust absorbed water rapidly, regained photosynthesis and nitrogenase activity, which were stabilized within 48 to 72 h of wetting. The dominant cyanobacteria in the crust were rich in carotenoid pigment, absorbing at 507 nm and mycosporine amino acid-like substances absorbing in UV only when desiccated and simultaneously exposed to bright sunlight. It is concluded that the highly active upper layers of and soils contain certain sheathed cyanobacteria that bind with soil particles forming a matrix protecting them from wind erosion. In addition, they are finely tuned in their physiology to the natural environmental conditions contributing organic matter and nitrogen through carbon and nitrogen fixation, thus increasing soil fertility.