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The intent of long-term ecological monitoring is to document changes in important properties of biological communities. At the least, a long-term monitoring system should be designed to detect long-term trends in three key attributes: soil and site stability, hydrologic function, and the biotic integrity of the system. There are four basic guidelines for developing integrated soil-vegetation monitoring systems for rangelands. These are: (1) identifying a suite of indicators which are consistently correlated with the functional status of one or more critical ecosystem processes and=or properties; (2) selecting base indicators on site specific objectives and resource concerns, and inherent soil and site characteristics;...
Microbiotic soil crusts play several important roles in many arid and semiarid ecosystems around the world. Their effects on soil hydrology, however, are poorly understood. It has been speculated that crusts (1) improve soil water availability by "sealing" the soil surface to water loss, or (2) diminish soil water by increasing the latent heat of a soil profile thereby increasing evaporation. In order to distinguish between these two opposing hypotheses, we analyzed water loss and temperature of soil profiles covered by different types of microbiotic soil crust (cyanobacteria, Psora decipiens, Placidium squamulosum) and a bare soil. We conducted experiments under growth chamber and field conditions. After watering...
Thermodynamics predict that in calcareous soils where the equilibrium activity of solution orthophosphate (Pso) is controlled by any calcium-phosphate mineral, calcium oxalate (CaC2O4) precipitation will increase Pso by depressing Ca2+ ion activity in soil solution and enhancing dissolution of the P-controlling mineral. Plants and/or associated microflora capable of imparting effective levels of oxalic acid (H2C2O4) to soil solution, may significantly improve their phosphorus nutrition via this mechanism. In previous work, we presented evidence for calcium oxalate (CaC2O4) formation in the rhizosphere of vesicular-arbuscular mycorrhizal (VAM) western wheatgrass (Agropyron smithii Rydb.). Herein, we report on further...
Soil surface growths dominated by cyanobacteria and the lichen Collema in southeastern Utah are shown to be associated with greater tissue content of several bio-essential elements in two co-occurring seed plants (Festuca octoflora, Poaceae, and Mentzelia multiflora, Loasaceae). The elements N, P, K, Ca, Mg, and Fe were present in significantly greater concentrations in Festuca growing on soils heavily encrusted with cyanobacteria and cyanolichens than in plants on the same soil where foot traffic had destroyed the cryptobiotic crusts. With Mentzelia, N, Mg, and Fe were present in significantly greater concentrations in plants from sites with encrusted soil surfaces than on blow-sand sites. The cryptobiota appeared...
Biological soil crusts of arid and semiarid lands contribute significantly to ecosystem stability by means of soil stabilization, nitrogen fixation, and improved growth and establishment of vascular plant species. In this study, we examined growth and nutrient content of Bromus tectorum, Elymus elymoides, Gaillardia pulchella, and Sphaeralcea munroana grown in soil amended with one of three levels of biological soil crust material: (1) a low-fertility sand collected near Moab, Utah; (2) sand amended with a 1-cm top layer of excised soil crust; and (3) crushed crust material. In addition, all plants were inoculated with spores of the arbuscular mycorrhizal fungus, Glomus intraradices. Plants were harvested after...
Rainfall simulation experiments were performed on 25 plots of varying microphytic crust cover in a wooded semiarid rangeland in eastern Australia. Under a rainfall intensity of 45 mm h-1, steady-state infiltration ranged from 5 mm h-1 to 41 mm h-1, but there was no effect of cover on this or any of the other soil hydrological variables measured. When disturbed plots with low cover (<15% cover) were excluded from the analyses, significant increases in time to ponding were associated with increases in crust cover. Despite some significant relationships, however, crust cover was an insignificant predictor of soil hydrological status at this site. We attribute this to the well-structured nature of the soils at the site,...
Recovery of soil properties from World War II-era military training exercises in the Mojave Desert was measured approximately 55 years following disturbance. Tracks from military vehicles were still visible, particularly in areas of desert pavement. Soil penetrability was much lower in visible tracks than outside the tracks. Soils in tracks had fewer rocks in the top 10cm of the soil profile than adjacent untracked soils. Larger particles (> 4.8mm) formed a moderately well-developed pavement outside of the tracks, while smaller, loose particles ( h 4.8mm) dominated the surface of the tracks. The time required to restore the desert pavement is likely to be measured in centuries. Based on biomass estimates, the cyanobacterial...
Cryptobiotic soil crusts are an important component of semiarid and arid ecosystems. An important role of these crusts is the contribution of fixed nitrogen to cold-desert ecosystems. This study examines the residual effects of various intensities and combinations of different surface disturbances (raking, scalping, and tracked vehicles) on nitrogenase activity, chlorophyll content, and chlorophyll degradation in these soil crusts. Nine months after disturbance chlorophyll content of disturbed soils was not statistically different from undisturbed controls, except in the scalped treatments, indicating recovery of this characteristic is fairly quick unless surface material is removed. Differences in chlorophyll degradation...