We investigated the effects of alpha grass Stipa tenacissima L.
Biogeochemical cycling[ edit ] Carbon cycling Biological soil crusts contribute to the carbon cycle through respiration and photosynthesis of crust microorganisms which are active only when wet. Respiration can begin in as little as 3 minutes after wetting whereas photosynthesis reaches full activity after 30 minutes.
Estimates for annual carbon inputs range from 0. Nitrogen fixation requires energy from photosynthesis products, and thus increase with temperature given sufficient moisture. Nitrogen fixed by crusts has been shown to leak into surrounding substrate and can be taken up by plants, bacteria, and fungi.
Nitrogen fixation has been recorded at rates of 0. Crust organisms contribute to increased soil stability where they occur. The increased surface roughness of crusted areas compared to bare soil further improves resistance to wind and water erosion. Aggregates of soil formed by crust organisms also increase soil aeration and provide surfaces where nutrient transformation can occur.
In areas where biological soil crusts produce rough surface microtopography, water is detained longer on the soil surface and this increases water infiltration. However, in warm deserts where biological soil crusts are smooth and flat, infiltration rates can be decreased by bioclogging.
Increased soil temperatures are associated with increased metabolic processes such as photosynthesis and nitrogen fixation, as well as higher soil water evaporation rates and delayed seedling germination and establishment.
These Aeolian deposits of dust are often enriched in plant-essential nutrientsand thus increase both the fertility and the water holding capacity of soils. The increased micro-topography generally increases the probability that plant seeds will be caught on the soil surface and not blown away.
Differences in water infiltration and soil moisture also contribute to differential germination depending on the plant species. It has been shown that while some native desert plant species have seeds with self-burial mechanisms can establish readily in crusted areas, many exotic invasive plants do not.
Therefore, the presence of biological soil crusts may slow the establishment of invasive plant species such as cheatgrass Bromus tectorum.
This can occur through N fixation by cyanobacteria in the crusts, increased trapment of nutrient-rich dust, as well as increased concentrations of micronutrients that are able to chelate to the negatively charged clay particles bound by cynaobacterial filaments.
Microarthropod populations also increase with more developed crusts due to increased microhabitats produced by the crust microtopography. Compressional and shear forces can disrupt biological soil crusts especially when they are dry, leaving them to be blown or washed away.
Thus, animal hoof impact, human footsteps, off-road vehiclesand tank treads can remove crusts and these disturbances have occurred over large areas globally. Once biological soil crusts are disrupted, wind and water can move sediments onto adjacent intact crusts, burying them and preventing photosynthesis of non-motile organisms such as mosses, lichens, green algae, and small cyanobacteria, and of motile cyanobacteria when the soil remains dry.
This kills remaining intact crust and causes large areas of loss. Invasive species introduced by humans can also affect biological soil crusts.
Invasive annual grasses can occupy areas once occupied by crusts and allow fire to travel between large plants, whereas previously it would have just jumped from plant to plant and not directly affected the crusts. Because crusts are only active when wet, some of these new conditions may reduce the amount of time when conditions are favorable for activity.
If they do not have enough moisture to photosynthesize to make up for the carbon used, they can gradually deplete carbon stocks and die. Without carbon and nitrogen available, they are not able to grow nor repair damaged cells from excess radiation. Conservation and management[ edit ] Removal of stressors such as grazing or protection from disturbance are the easiest ways to maintain and improve biological soil crusts.
Protection of relic sites that have not been disturbed can serve as reference conditions for restoration. There are several successful methods for stabilizing soil to allow recolonization of crusts including coarse litter application such as straw and planting vascular plants, but these are costly and labor-intensive techniques.
Spraying polyacrylamide gel has been tried but this has adversely affected photosynthesis and nitrogen fixation of Collema species and thus is less useful. Other methods such as fertilization and inoculation with material from adjacent sites may enhance crust recovery, but more research is needed to determine the local costs of disturbance.The Negev Desert in Israel is a mosaic of macrophytic patches, consisting of shrubs and annual plants growing in a soil mound, and microphytic patches, consisting of algae, cyanobacteria, bacteria, mosses, and lichens growing on a soil crust.
Biological soil crusts are also known as cryptogamic, microbiotic, cryptobiotic, and microphytic crusts, leading to some confusion.
The names are all meant to indicate common features of the organisms that compose the crusts. Biological soil crusts are communities of living organisms on the soil surface in arid and semi-arid ecosystems. They are found throughout the world with varying species composition and cover depending on topography, soil characteristics, climate, plant community, microhabitats, and disturbance initiativeblog.comical soil crusts perform important ecological roles including carbon fixation.
Soil surfaces in arid and semi-arid lands often lack photoautotrophic life but are covered by a community of soil surface organisms that are adapted to aridity and thus able to tolerate dehydration.
microphytic soil crusts, or here simply biocrusts) are crucial components of terrestrial ecosystems. These crusts are essential for aggregating mineral particles at the soil surface. Soil C and N pools in patchy shrublands of the Negev and Chihuahuan Deserts Thomas L.
Thompsona,, Eli Zaadyb,c, and biological soil crusts. Within such ecosystems ‘‘fertile C4 grasses and soil crusts dominating microphytic patches.