Effects of Altered Temperature and Precipitation on Desert Protozoa Associated with Biological Soil Crusts

Abstract

Biological soil crusts are diverse assemblages of bacteria, cyanobacteria, algae, fungi, lichens, and mosses that cover much of arid land soils. The objective of this study was to quantify protozoa associated with biological soil crusts and test the response of protozoa to increased temperature and precipitation as is predicted by some global climate models. Protozoa were more abundant when associated with cyanobacteria/lichen crusts than with cyanobacteria crusts alone. Amoebae, flagellates, and ciliates originating from the Colorado Plateau desert (cool desert, primarily winter precipitation) declined 50-, 10-, and 100-fold, respectively, when moved in field mesocosms to the Chihuahuan Desert (hot desert, primarily summer rain). However, this was not observed in protozoa collected from the Chihuahuan Desert and moved to the Sonoran desert (hot desert, also summer rain, but warmer than Chihuahuan Desert). Protozoa in culture began to encyst at 37 degrees C. Cysts survived the upper end of daily temperatures (37-55 degrees C), and could be stimulated to excyst if temperatures were reduced to 15 degrees C or lower. Results from this study suggest that cool desert protozoa are influenced negatively by increased summer precipitation during excessive summer temperatures, and that desert protozoa may be adapted to a specific desert's temperature and precipitation regime.

Biocrusts in the Context of Global Change

“…Entering and exiting these dormant states is metabolically costly for the individual, and some species do not tolerate frequent wetting by precipitation or rehydration during high temperatures. Thus, the combination of frequent wetting cycles in the presence of elevated temperatures is expected to cause more mortality of microfauna than either frequent wetting in mild temperatures or extreme temperatures while anhydrobiotic alone (Darby et al 2006(Darby et al , 2011. Changes in drought will also likely affect biocrust-plant interactions (see Chap.…”

Microfauna Within Biological Soil Crusts

“…In arid systems, nematodes can be found as deep as 11-12 m (Freckman and Virginia 1989), but the peak abundance of microfauna in soils covered by biocrusts is usually within the top 10-20 cm. In most soils, protozoa, nematodes, and microarthropods are more abundant in the surface 0-10 cm than in the next 10-20 cm or 20-30 cm (Darby et al 2006(Darby et al , 2007a(Darby et al , b, 2010Housman et al 2007;Neher et al 2009). However, the proportion of microfauna that are anhydrobiotically inactive is inversely proportional to soil moisture or relative humidity, and relative humidity in soils below 10 cm is generally greater than in surface 0-10 cm soils.…”

“…This is generally true for all ecosystems, but it is easier to quantify in arid systems with more sparsely distributed vascular plants. Furthermore, microfauna are more abundant and taxonomically diverse beneath and associated with late-successional stage "dark" lichen and moss biocrusts than when associated with early-successional stage "light" cyanobacteria biocrusts (Darby et al 2006(Darby et al , 2007a(Darby et al , b, 2010. This can reasonably be explained, as greater productivity and microbial prey biomass is found in lichen and moss biocrusts than in cyanobacteria crusts.…”

“…First, the generation time of omnivore nematodes in the order Dorylaimida was set to 50 days per year, representative of the slowergrowing omnivore-predators in the desert such as Aporcelaimellus and Qudsianematidae (Wood 1973a, b). Second, the generation time of all protozoa was decreased from 6.67 days to 2 days, which is a conservative estimate of the maximum growth rate (0.5 per day) of these desert protozoa (Darby et al 2006). Finally, microphytophagous prostigmatid and oribatid mites, collembolans, tardigrades, and tylench-and dorylaim-type omnivores were assumed to prey on cyanobacteria with the same preferences as on saprophytic fungi (Neher et al 2009;Wood 1973a;Yeates et al 1993).…”

Impact of biological soil crusts and desert plants on soil microfaunal community composition

“…Protozoa were enumerated from soils using a most probable number technique according to Darbyshire et al (1974) with the following modifications (Darby et al 2006). Sterilized soil extract (6% w/v) was used as the diluent for MPN dilutions.…”