Response of cyanobacterial soil crusts to moisture and nutrient availability

• Moisture content > 14% is necessary to sustain cyanobacterial photosynthetic activity.
• Nutrients promoted an increase in cyanobacterial biomass over longer periods > 4 weeks.
• Moisture frequency and magnitude are important to landscape stability via crusts.

Cyanobacterial soil crusts play an important role in arid ecosystems and in stabilising dryland soils. Such arid regions are prone to extreme environmental conditions such as prolonged drought and short-lived intense rainfall and flood events, yet the impact of such events on cyanobacterial growth, and hence their role in landscape stability, is poorly-understood. This paper presents a series of laboratory experiments which determine cyanobacterial soil crust response to moisture and nutrient availability. Photosynthetic yield measurements indicate a rapid response in cyanobacterial response following hydration and suggest moisture content > 14% (c. 1.5 mm rainfall equivalent) is necessary to sustain such activity. The addition of nutrients did not trigger any significant increase in crust metabolic activity or photosynthetic response compared with deionised water over a 7-day period. However, over longer periods (> 4 weeks) nutrient-enriched rainfall promoted an increase in cyanobacterial metabolic growth measures (chlorophyll a and ‘greenness’) compared with deionised water. From the results we can infer that the magnitude and frequency of hydration from rainfall and flood events in arid regions play an important role in the maintenance of cyanobacterial soil crusts. Predicted changes in dryland hydrological regimes, for example changing frequency and intensity of rainfall in the Australian arid zone as a consequence of climate shifts, may therefore have an impact on the ability of cyanobacterial crusts to promote landscape stability.