The Effects of Moisture on Acetylene Reduction by Mats of Blue-green Algae in Sub-tropical Grassland

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Abstract
During the dry winter months desiccation is the main factor preventing nitrogen fixation by mats of blue-green algae in kikuyu lawns. In the wetter summer months a few days of sunshine without rain will dry out the algal mats and depress nitrogen fixation unless the algae are protected by swards of grass. Dry mats resume nitrogen fixation within an hour of becoming damp and attain their normal rate of fixation within 5 h. Maximum fixation rates occur at 100 per cent relative humidity and with soil moisture contents of 22 to 42 per cent. Dry algal mats are unable to take up sufficient water as vapour (even in saturating conditions) to permit resumption of acetylene reduction. Algal-dominated soils show greater water retention than adjacent bare soils.