The effect of slope orientation and soil particle size on a microfloral community in a desert ecosystem
Desert ecosystems are characterized by harsh abiotic conditions, with high radiation and low annual rainfall that is unpredictable in time, frequency, and dispersion. The differences in abiotic conditions between north- and south-facing slopes are very significant. These differences led to evolutionary processes on both slopes that caused unique adaptations of the living organisms to the environmental conditions. Slope orientation and location along the slope have been found to exhibit significant differences in the ratio between the particle size fractions as result of abiotic environment. As soil structure and composition are the main factors in determining soil microbial-community composition, structure, and diversity, we hypothesized that slope orientation, location along the slope, and soil particle size will determine microbial community diversity and composition. Soil samples (n=4) were collected seasonally from the 0-5 cm depth from the top, middle, and bottom sites of both the north- and south-facing slopes. The wadi channel was used as a control. Each sample was fractionated into 3 particle size fractions: sand (0.25 - 2.0 mm), silt (0.037 - 0.25mm) and clay (<0.037), while part of the soil samples remained unfractionated. Soil moisture, organic carbon, electrical conductivity, microbial biomass, microbial respiration, Shannon index of diversity, and CLPP were determined for each fraction.
Soil moisture and soil organic-carbon content varied seasonally and were found to be highest at the top location of the north-facing slopes, and they decrease with the decrease in soil particle size. Microbial biomass, CO2 evolution, and functional diversity of the microbial population showed seasonal variation, with differences between the slopes and particle size fractions. Functional diversity was found to be higher is the wet seasons (winter and spring) along the south-facing slope and in the dry seasons (summer and autumn) in comparison to the north-facing slope. The uniqueness of using the two-slope (north and south) system was that it hightlites the difference in temporal and spatial physical and biotic components. Slope aspect modifies and influences ecological processes and contributes to habitat heterogeneity by influencing microclimate and biotic composition.