Crust Cover Research Articles

Spatial heterogeneity of <i>Cladonia rangiformis</i> and <i>Erica</i> spp. induces variable effects on soil microbial communities which are most robust in bare-soil microhabitats

Abstract. Biological soil crust (BSC) is an essential part of arid and semiarid regions; however information concerning the spatial heterogeneity of the interactions between crust, plants and soil microbes is limited. Sampling was confined to an area either covered with Erica spp. shrubs interspaced by crust cover (Cladonia rangiformis) or uncovered by crust. Along a straight line of 100 cm from the base of the shrubs towards their periphery and at successive distances of 20 cm, soil samples were collected once. The biomass, the composition and the network of interactions among the members of the soil microbial communities as well as the activity of soil enzymes involved in the C, N and P cycle were estimated. Crust coverage exerted a significant allelopathic negative effect on soil microbial biomasses due to the leaching of lichen's antimicrobial substances. In contrast, the crust effect on enzyme activity was positive, probably due to the amelioration of soil abiotic conditions. The distance from the base of Erica spp. affected the total microbial and bacterial biomass, with lower values at the base of the shrubs. The composition of microbial communities between the different sampling points exhibited significant dissimilarities. Network analysis revealed that in uncrusted soils the most connected microbial network was at samples collected from a distance of >60 cm (bare soils), while in crusted soils this was at samples collected at the base of shrubs. We concluded that microbial biomass showed limited response to spatial heterogeneity, while the composition and the topology of interactions among the microbial members reflected a heterogeneous soil environment existing on a small spatial scale in Mediterranean areas. The microbial community in bare soil appeared to be the most robust against future disturbances.

Spatial cover and carbon fluxes of urbanized Sonoran Desert biological soil crusts

Biological soil crusts (BSC) are important contributors to nutrient cycling in arid environments such as the Sonoran Desert. BSC at an urban (University Indian Ruins) and at a non-urban site (Santa Rita Experimental Range) were compared to determine if their structure or function was influenced by proximity to an urban environment. The Step Point method was used in the field to determine ground cover; which was found to be similar between sites. However, the spatial distribution of the BSCs was significantly different, such that more BSCs were found under plants at the non-urban site (P < 0.05). Relative gross photosynthesis was measured in the lab by addition of a watering event. Gross photosynthesis was found to be higher in the non-urban BSCs (P < 0.001), indicating lowered productivity in urban BSCs due to effects caused by proximity to urban environments. This study provides evidence that BSCs at urbanized sites are affected functionally, and therefore may be contributing differently to carbon and nitrogen cycling in these ecosystems.

What Is Driving the Proliferation of Exotic Annual Grasses in Sagebrush Communities? Comparing Fire with Off-Season Grazing

Exotic annual grass invasion is a pressing concern in sagebrush rangelands of the western United States. Overgrazing and fire have historically both been implicated in the rise of annual grasses, but experiments that compare the effect of grazing versus fire are lacking, particularly for contemporary grazing practices such as off-season (fall and winter) grazing. We compared 1) burned and ungrazed (burned), 2) off-season, moderately grazed and unburned (grazed), and 3) ungrazed and unburned (control) treatments at five Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis [Beetle & A. Young] S.L. Welsh) sites in southeastern Oregon for half a decade. Fire, but not off-season grazing, substantially increased exotic annual grass cover and abundance. Vegetation cover and density were generally similar between grazed and control areas. In contrast, at the end of the study exotic annual grass cover and density were over fourfold greater in burned areas. Exotic annual grass became the dominant plant group in burned areas, but not in grazed and control areas. Cover and density of annual forbs, predominately non-native species, were generally greater in the burned compared with grazed and control treatments. Fire also decreased soil biological crust cover and sagebrush cover and density compared with grazed and control treatments. This study provides strong evidence that fire is a threat to the sustainability of Wyoming big sagebrush communities at risk of exotic annual grass dominance, but that off-season, moderate grazing poses little risk. However, considering the spatial extent of our study was limited, further evaluations are needed across a larger geographic area. Given that off-season grazing can decrease the probability of fire, off-season grazing may be a valuable tool to reduce the risk of exotic annual grass dominance.

Moderate Grazing During the Off-Season (Fall-Winter) Reduces Exotic Annual Grasses in Sagebrush-Bunchgrass Steppe

Exotic annual grass invasion and dominance of sagebrush-bunchgrass steppe is a concern because it decreases biodiversity and promotes frequent wildfires. Management is needed to reduce exotic annual grasses to prevent sagebrush-bunchgrass communities from transitioning to annual grasslands. Grazing during the off season (fall-winter) has shown promise at reducing exotic annual grasses, but it has not been evaluated in plant communities dominated by sagebrush and native bunchgrasses. We compared moderate grazing during the off season with not grazing in five Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis [Beetle & A. Young] S.L. Welsh)−bunchgrass communities in the northern Great Basin. Treatments were applied annually for 10 yr (2009−2010 through 2018−2019). Plant community characteristics were measured after treatments had been applied from 6 to 10 yr. Off-season grazing reduced exotic annual grass density and cover. After a decade, annual grass cover was twofold greater in ungrazed areas. Sandberg bluegrass (Poa secunda J. Presl) density increased with off-season grazing, but large bunchgrass density was similar between off-season grazed and ungrazed areas. Perennial and annual forb density and cover were similar between off-season grazed and ungrazed treatments. Biological soil crust cover was also similar between off-season grazed and ungrazed areas. The results of this study provide strong evidence that off-season grazing has application for managing exotic annual grasses in sagebrush-bunchgrass steppe. Considering the vast scope of the exotic annual grass problem, properly applied grazing may be the most cost-efficient tool to mediate the impacts of annual grass invasion.

Evolution of fluid flow and carbonate recrystallization rates in deep-sea sediments of the Equatorial Pacific

Fluid flow and carbonate recrystallization rates of deep-sea sediments from eight locations in the Equatorial Eastern Pacific were determined by using δ44/40Ca values of pore water and corresponding sediments. The studied drill sites of IODP Exp. 320/321 are located along a transect of decreasing crustal age and reveal different characteristic pore water depth profiles. The younger sites show an overall isotopic equilibration with the sediment in the upper part of the sedimentary column. In the lower part, the δ44/40Ca of the pore water increases back to seawater-like values at the sediment/basalt interface, forming a bulge-shaped pore water profile. The magnitude of the δ44/40Ca pore water bulge decreases with increasing age of the oceanic crust and sediment cover, resulting in seawater-like δ44/40Ca values throughout the sedimentary column in the oldest Sites U1331 and U1332. These findings indicate a seawater-like fluid input from the underlying crust into the sediment. Thus, after sedimentation, carbonate recrystallization processes start to enrich the pore water in 40Ca, and after a time of carbonate recrystallization and cooling of oceanic crust, a flow of seawater-like fluid starts to move upwards through the sedimentary column, enriching the pore water with 44Ca. We established a carbonate recrystallization and fluid flow model to quantify these processes. Our determined carbonate recrystallization rates between 0.000013e(−t/15.5) and 0.00038e(−t/100.5) and fluid flow rates in the range of 0.42–19 m*Myr−1 indicate that the fluid flow within the investigated sites of IODP Exp. 320/321 depends on the sedimentary composition and location of the specific site, especially the proximity to a recharge or discharge site of a hydrothermal convection cell.

Combined impact of moss crust coverage rates and distribution patterns on wind erosion using beryllium-7 measurements

Although biological soil crusts (BSCs) provide considerable control over wind erosion in arid and semiarid regions, understanding of BSCs coverage rates and distribution patterns impacts on wind erosion is remain limited, which further causes poor quantification of BSCs factors in wind erosion prediction models. This study estimated wind erosion affected by moss crust coverage rates and distribution patterns using the weighting approach and beryllium-7 measurements through wind tunnel experiments, and screened factors that significantly influence wind erosion based on landscape metrics and multiple linear regression. Results showed that both moss crust coverage and distribution pattern significantly affected wind erosion and deposition. When moss crust coverage increased from 10% to 80%, average erosion rates in bare soil areas of trays almost all decreased logarithmically from 623.0 to 27.4 g m−2 min−1, while the average deposition rates in moss crust covered areas decreased from −21.7 to −16.7 g m−2 min−1. Moss crust located at the middle area of trays (SCS) showed better overall erosion control effects, while moss crust located at downwind of sand (SC) showed better sediment trapping effects compared to other distribution patterns when moss crust coverage was the same. The SCS and SC patterns decreased wind erosion and deposition rates reached up to 81.9% and 38.0%, respectively. Moreover, wind erosion rates when arranged moss crust parallel to the wind direction resulted in significantly higher soil erosion (i.e., by a factor up to 7.3) compared to that of perpendicular to the wind direction. Stepwise regression showed that only wind velocity and moss crust coverage were included in the linear regression equation with a relatively low R2 value (R2 = 0.35), but excluded other landscape metrics. This is indicated the importance of developing composite indices and their associative algorithms should be considered when quantifying spatial distribution impacts of BSCs on wind erosion.

Combining a saltation impact sensor and a wind tunnel to explore wind erosion processes—A case study in the Zhundong mining area, Xinjiang, China

The properties of surface soil determine its erodibility, the wind force determines the soil erosion intensity, and both factors determine the amount of soil erosion. In the Zhundong mining area in Xinjiang, China, continuous mining and construction activities in the past 10 years have resulted in the destruction of surface crust formed by precipitation, the gradual refinement of soil, and an increase in erodibility. To accurately describe the impact of human construction on local wind erosion, we installed a saltation impact sensor in a wind tunnel to explore the soil responses to wind erosion and changes in the wind erosion rate caused by anthropogenic interference. We artificially manipulated the soil moisture, crust coverage, and particle size, and subjected the soils to different wind speeds. The results show that, first, in soil crust and moisture experiments, a sensor can effectively monitor the process and amount of wind erosion, but the monitoring efficiency of the sensor is greatly reduced after an overall change in soil particle size. Second, the wind erosion processes in the three test groups are roughly the same: the wind starts to drive the soil particles to move for the first 0 to 30 s. Then, the number of released soil particles increases rapidly with increasing wind speed from 30 to 240 s, gradually decreases after the wind speed stabilizes from 240 to 480 s, and then remains consistent after 480 s. Third, a uniform distribution of the crust rather than a concentrated distribution of the crust can reduce soil erosion by 20%. The presence of a crust can effectively prevent erosion in the early stage of wind erosion, and the more complete the surface crust on the soil, the better it can resist continuous wind erosion. Fourth, moisture in the soil effectively impedes erosion by increasing the wind speed required to move particles in the early stage; however, continuous erosion decreases the soil moisture, and the proportion of eroded soil gradually increases in the later stage. Fifth, the erosion rate data show that particle size change can result in a maximum wind erosion rate of 2,599 g m^–2 min^–1 and is the most influential factor for wind erosion.

Effects of climate change and land use intensification on regional biological soil crust cover and composition in southern Africa

Biological soil crusts (biocrusts) form a regular and relevant feature in drylands, as they stabilize the soil, fix nutrients, and influence water cycling. However, biocrust forming organisms have been shown to be dramatically vulnerable to climate and land use change occurring in these regions.In this study, we used Normalized Difference Vegetation Index (NDVI) data of biocrust-dominated pixels (NDVIbiocrust) obtained from hyperspectral and LANDSAT-7 data to analyse biocrust development over time and to forecast future NDVIbiocrust development under different climate change and livestock density scenarios in southern Africa. We validated these results by analysing the occurrence and composition of biocrusts along a mesoclimatic gradient within the study region.Our results show that NDVIbiocrust, which reached maximum values of 0.2 and 0.4 in drier and wetter years, respectively, mainly depended on water availability. A predicted decrease in rainfall events according to all future climate scenarios combined with increased temperatures suggested a pronounced decrease in NDVIbiocrust by the end of the 21st century caused by reduced biocrust coverage. Livestock trampling had similar effects and exacerbated the negative impacts of climate change on biocrust coverage and composition. Data assessed in the field concurred with these results, as reduced biocrust cover and a shift from well-developed to early stages of biocrust development were observed along a gradient of decreasing precipitation and increasing temperatures and livestock density.Our study demonstrates the suitability of multi-temporal series of historical satellite images combined with high-resolution mapping data and Earth system models to identify climate change patterns and their effects on biocrust and vegetation patterns at regional scales.

Understory shading exacerbated grassland soil erosion by changing community composition

The importance of understory herbs for soil erosion controlling in forests is well accepted, but its effectiveness was rarely reported. Understanding how understory shading affects herbs growth and soil erosion controlling benefits is essential for better policy management. Here, we investigated grassland characteristics and soil erosion process before and after grasslands placed beneath the forest canopies. Four typical grasslands (Trifolium repens, Medicago sativa, Elymus dahuricus and Bromus inermis) of the Loess Plateau were selected, and bare land was used as the control. Total fifteen plots (three replicates for each treatment) with a slope of 20° were constructed. All plots were placed outdoor (open areas) in the first year, and were moved to the undergrowth and remained in the Sophora japonica and Populus cathayana forests over the next five years. Time to runoff, runoff volume and sediment yield were examined by two simulated rainfall experiments before and after understory shading. Results showed that understory shading promoted the disappearance of the original grass species, increasing weeds with poor roots. Further, these changes led to more soil loss in all understory grassland treatments. After understory shading, the runoff volume (67.0–125.5 L) and biological soil crust coverage (1.0–15.7%) significantly decreased for all plots, whereas the sediment yield (5.0–1650.5 g), species richness (>5) and litter mass (75.8–241.0 g) significantly increased. Therefore, understory shading changed the community composition and structure of understory grasslands. Besides, we found that herb species difference, but not species richness difference, more determined understory soil erodibility. Our findings indicate that the shade-tolerant herb species application could effectively reduce soil erosion in forest-grassland complex ecosystem will help to achieve the sustainability of understory grassland during vegetation restoration.

Effectiveness of typical plant communities in controlling runoff and soil erosion on steep gully slopes on the Loess Plateau of China

Vegetation restoration is widely recognized as the most effective measure in controlling runoff and soil erosion under different climatic zones and topographical conditions. Nevertheless, few studies have been performed to quantify its effectiveness in controlling runoff and soil erosion on steep gully slopes in arid and semi-arid regions. This study was conducted to quantify the effectiveness of vegetation restoration in controlling runoff and soil erosion and further identify its main factors influencing runoff and soil erosion under typical plant communities on steep gully slopes of the Loess Plateau, China. Runoff and erosion were analyzed on monthly scale from 14 micro-plots for three consecutive years (2018–2020). The results showed that vegetation restoration can effectively reduce runoff and erosion. Compare to bare land, runoff and erosion reduced by 37.5% to 93.0% and 83.9% to 99.6% under different plant communities. The mean percent runoff and soil erosion reduction and the ratio of percent runoff reduction to percent erosion reduction of shrub community were 1.34, 1.06, and 1.29 times those of grass community. The corresponding values of grass community with tap root systems were 0.60, 0.91, and 0.64 times that with fibrous root systems. Shrub community was more effective than grass community in reducing erosion, whereas grass community (especially with tap root systems) was more effective in maintaining runoff. Although runoff and erosion varied greatly between different plant communities, their relationships could be well simulated by power functions. Variations in runoff were primarily affected by rainfall amount, the maximum 30-minute intensity, 60-minute rainfall kinetic energy, litter coverage, and biological crust coverage. Variations in erosion were dominantly influenced by runoff, the maximum 30-minute intensity, plant canopy coverage, and litter density. Overall, our study suggested that grass community (especially with tap root systems) is likely a more suitable and advisable choice for vegetation restoration on steep gully slope in arid and semiarid regions. The results of this study provide the scientific guide for policy-making of vegetation restoration on steep gully slopes in arid and semi-arid regions, i.e. the Loess Plateau.

Plant litter crust appear as a promising measure to combat desertification in sandy land ecosystem

Desertification is one of the most alarming forms of land degradation that threatens the functioning of dryland ecosystems. Ecological restoration of ecosystem functioning in sandy land has become a worldwide urgent research issue. In this study, the effects of plant litter crust (plant litter from poplar leaves of the surrounding area and sand grains bonded together due to interaction of water erosion and wind erosion) on surface soil properties and the loamification process of sandy soil were assessed in a semi-arid sandy land ecosystem at the edge of Mu Us sandy land by the field experiment sampling and indoor analysis. Soil structure and nutrient content were measured at two depths (0–5 cm and 5–10 cm) of bare sandy soils (as control), the soils beneath of the biological soil crust and the three stages of plant litter crusts (1-, 3- and 5-years old). We found that plant litter crust cover significantly improved soil structure and soil moisture through increasing soil macro-aggregates, clay and silt sized grains content, and total soil porosity, and decreasing soil temperature. Significant differences were observed in the content of total nitrogen and available soil phosphorous and potassium among the different types of crust and bare sandy soil. In the 0–5 cm soil depth, the available phosphorous of 3- and 5-years litter curst were 71% and 94% higher than that of bare sandy soil, respectively. These results suggest that plant litter crust functioned as a driving force to promote the loamification process through modifying sandy soil surface properties. This study proves the critical role played by the plant litter crust in the ecological restoration of semi-arid sandy land ecosystem. Besides, the hypothesis that plant litter crusts have great potential in combating desertification is correct and should be considered as an appropriate measure for ecological restoration in sandy areas.

Biological crust in sand and dust storm source areas of Asia and its impact on dust emission

Even though the biological crusts are critical to dust emissions, no sand and dust forecast model have considered the impacts of the biological crust in dust emission scheme. This situation mainly comes from two scientific difficulties: there is no large scale regional biological crust data available that can be used in the forecast model; there is no quantification of how biological crusts impact on sand emission. In this way, we studied the distribution of biological soil crust in sand and dust storm source areas of Central and East Asia using Moderate Resolution Imaging Spectroradiometer satellite surface reflectance data collected in 2000–2019 to determine its potential impact on dust emission according to two empirical schemes. We further evaluated the relationships between soil crust coverage, roughness length, and dust emission to study SDS source areas. We found that biological crust is widely distributed in SDS source areas of Central and East Asia, with coverage rates of 19.8% in Central Asian deserts, 23.1% in the Gobi Desert, and 17.3%–32.8% in Chinese deserts (p > 0.05). Cyanobacteria and lichen coverage has increased in Chinese deserts, reflecting the recent impacts of the Project of Returning Farmland to Grassland and Farmland to Forests. However, biological soil crust coverage has not increased in Central Asian deserts or the Gobi Desert, and that in Central Asian deserts continues to decrease, demonstrating the complexity of the combined effects of human activities and climate change on its distribution. Biological soil crust increased the roughness length of Central and East Asian SDS source areas by 0.14–0.62 mm. The suppression of dust emission due to biological soil crust did not change among years during the study period. The horizontal and vertical dust flux inhibition coefficient (DFIC) were 2.0–11.0 and 1.7–2.9 (p > 0.05), respectively, clearly showing a suppressive effect. Improvement of the ecological environment in some deserts can lead to the ability of these crusts to inhibit dust erosion errors that must be considered in the dust emission scheme for areas where crust coverage has improved.

Influence of physical crust cover on the wind erodibility of soils in the inland Pacific Northwest, USA

AbstractSoil crusts are especially important for agricultural fields in the inland Pacific Northwest where there is a high wind erosion risk due to exposure of fine erodible soils in fallow croplands. The objective of this study was therefore to evaluate the effect of physical soil crust cover on wind erosion and identify critical soil crust cover amounts to control wind erosion. The effect of crust cover of five loessial soils on wind erosion was tested in a wind tunnel. The results indicated that crust cover appeared to have little influence on soil loss until crust cover was &gt; 30%. Soil loss at this percentage of crust cover was 55.04% to 68.08% lower as compared with a soil surface devoid of crust cover for the five soil types. The relationship between soil loss and crust cover appeared to be nearly a linear function, although an exponential function also provided a good fit to the data. With progressive development of a crust cover, the rate of change in soil loss varied among soil types. From 0 to 100% crust cover, the rate of change in soil loss ranged from −312.8 g m−2 for Palouse silt loam to −1449.1 g m−2 for Warden sandy loam. The rate was not only associated with intrinsic soil erodibility, but also crust stability and abrasion flux. Due to the lower intrinsic soil erodibility and greater crust stability, Palouse silt loam crust was characterized by lower flaking potential and limited abrasion flux relative to the other tested soil types. The Single‐event Wind Erosion Evaluation Program (SWEEP) was used to simulate and identify the effect of crust cover on erosion processes. Differences between simulated and measured soil loss suggest that cracks in soil crusts may affect soil loss and should be incorporated into the SWEEP to expand the model capability for representing crusted soils.

Spider Community Variability and Response to Restoration in Arid Grasslands of the Pacific Northwest, USA.

Simple SummarySpiders contribute greatly to biodiversity and play important roles in terrestrial food webs, yet we know very little about the types of spiders that live in semi-arid grasslands in the Pacific Northwest, USA. As interest in the conservation of biodiversity and restoration of these imperiled ecosystems grows, it is imperative that we not only describe spider communities (i.e., groups of interacting species) in these areas, but also investigate environmental factors that influence them, and how they respond to restoration. This information can help guide land managers as they design restoration and management plans. Our goals were threefold: (1) describe variability in spider communities in three semi-arid grasslands of the Pacific Northwest, (2) identify environmental variables that may influence spider communities, and (3) determine whether spiders or environmental variables differ between actively vs. passively restored sites. We found that spider communities varied greatly among three superficially similar locations and patterns corresponded to differences in elevation and cover of invasive grass, litter, biological soil crust, and flowering plants. We found no differences between spider communities in active and passive restoration treatments, indicating that if the primary goal of restoration is to increase biodiversity, additional factors must also be manipulated.Grassland restoration in North America has intensified but its impact on major invertebrate groups, including spiders, is unclear. We studied three grassland locations in the Pacific Northwest, USA, to (1) describe variability in spider communities, (2) identify environmental variables that may underlie patterns in spider communities, and (3) determine whether spiders and environmental variables differ between actively (removal of disturbances, then plant with natives) vs. passively restored sites (removal of disturbance only). We found spider richness, diversity, and composition differed among the three locations but abundance did not. Sites with more litter and invasive grass cover had more spiders while sites at higher elevation and with more forb and biological soil crust cover had increased spider richness and diversity. Spider community composition was associated with elevation and litter cover. Surprisingly, no spider community or environmental variables differed between actively and passively restored sites, except that litter cover was higher in passively restored sites. This study demonstrates that even in superficially similar locations, invertebrate communities may differ greatly and these differences may prevent consistent responses to active vs. passive restoration. If increasing biodiversity or the abundance of invertebrate prey are goals, then environmental factors influencing spider communities should be taken into account in restoration planning.

Hillslope geodiversity effects on properties and composition of biological soil crusts in drylands

AbstractBiological soil crusts (biocrusts) play important roles in ecosystem functioning and are considered ecosystem engineers: stabilizing the soil surface, preventing soil erosion, changing soil surface hydrology, and enriching the soil with carbon and nitrogen. The link between geodiversity and biodiversity incorporates physical aspects from geology, geomorphology and pedology. We aimed to assess the effects of hillslope geodiversity on the cover, composition and biophysiological properties of biological soil crusts (biocrusts) in a dryland ecosystem. The geodiversity of the hillslope is determined by the stone cover on the ground surface, the content, stones in the soil profile, and the soil depth. It is known from the scientific literature that geodiversity affects biodiversity; thus, we hypothesized that the hillslope type may affect biocrust properties that develop on these hillslopes. The results indicate that the mean covers of biocrust types in the homogeneous (low geodiversity) hillslopes were 60.6% cyanobacterial crusts and 39.4% biocrusts composed of cyanobacteria, moss and lichens, whereas those of the heterogeneous (high geodiversity) hillslopes were 81.6% cyanobacterial crusts and 18.4% biocrusts composed of cyanobacteria, moss and lichens. It was concluded that geodiversity enhances the growth of biocrust species that require higher soil moisture. The results imply that wherever restoration activities are planned, and especially in drylands, the geodiversity of the area should be taken into account.Highlights Geodiversity expressed by the degree of stoniness impacts ecosystem functioning and soil properties Geodiversity impacts the biocrust's cover and composition Geodiversity enhances the growth of biocrusts that require high soil moisture Chlorophyll a, b and a + b in biocrusts are increased in heterogeneous hillslopes

About the energy and age of the plate tectonics

AbstractRecently, a number of research findings have come to light about the age of plate tectonics, and energies are needed to operate it. The aim of present study is to investigate whether the energy of plate tectonics process was different during the Phanerozoic (Pz) and in earlier eons, and if there is such a discrepancy, whether it can be justified by changes in the processes that able to move the plates. The study will track temporal changes in important components of plate tectonics such as length of mid‐ocean ridges, subduction zones and relative oceanic crust coverage during Phanerozoic. Next, it will be examined how the knowledge gained in this way can be reconciled with the results of studies of previous eons. It was found that the temporal variation in kinetic energy of axial rotation due to changes in length of day (LOD) can be assumed as a determining energy which acts on the tectonic plates as in the Phanerozoic as earlier in Archean (Arch) and Proterozoic (Ptz).

Muted responses to chronic experimental nitrogen deposition on the Colorado Plateau.

Anthropogenic nitrogen (N) deposition is significantly altering both community structure and ecosystem processes in terrestrial ecosystems across the globe. However, our understanding of the consequences of N deposition in dryland systems remains relatively poor, despite evidence that drylands may be particularly vulnerable to increasing N inputs. In this study, we investigated the influence of 7 years of multiple levels of simulated N deposition (0, 2, 5, and 8kgNha-1year-1) on plant community structure and biological soil crust (biocrust) cover at three semi-arid grassland sites spanning a soil texture gradient. Biocrusts are a surface community of mosses, lichens, cyanobacteria, and/or algae, and have been shown to be sensitive to N inputs. We hypothesized that N additions would decrease plant diversity, increase abundance of the invasive annual grass Bromus tectorum, and decrease biocrust cover. Contrary to our expectations, we found that N additions did not affect plant diversity or B. tectorum abundance. In partial support of our hypotheses, N additions negatively affected biocrust cover in some years, perhaps driven in part by inter-annual differences in precipitation. Soil inorganic N concentrations showed rapid but ephemeral responses to N additions and plant foliar N concentrations showed no response, indicating that the magnitude of plant and biocrust responses to N fertilization may be buffered by endogenous N cycling. More work is needed to determine N critical load thresholds for plant community and biocrust dynamics in semi-arid systems and the factors that determine the fate of N inputs.

Effect of water availability on induced cyanobacterial biocrust development

Cyanobacteria inoculation has recently become an innovative biotechnological tool for restoring degraded arid soils. A major challenge for researchers, however, is the search for suitable species able to cope with water stress under field conditions. The aim of this study was to test the effect of water availability on induced biocrust growth in three different degraded soils from semiarid areas of Almeria (Spain). Three native N-fixing cyanobacterial strains, Nostoc commune, Scytonema hyalinum and Tolypothrix distorta, were inoculated on soil samples from the study areas, individually and as a consortium. Two different irrigation treatments simulating the water availability in the selected areas, in a dry year (180 mm/year) and a wet year (380 mm/year), were applied for three months under laboratory conditions. Cyanobacteria cover, chlorophyll a spectral absorption (Chla spectral absorption), soil organic carbon (SOC) and total exopolysaccharide (EPS) gains were measured as indicators of biocrust development. Cyanobacteria crust cover, SOC and EPS gains were higher in inoculated soils than in uninoculated soils. Even though the hydration regime had a generally significant effect on cyanobacteria cover, Chla spectral absorption and EPS, similar biocrust development and improvement in edaphic conditions were observed under both hydration regimes for all treatments. Of the candidate inoculants, N. commune showed remarkably higher performance under dry conditions than the rest, providing evidence of high potential for growing under water-limited conditions and being a good candidate inoculant for restoration of arid degraded areas.

Crust cover and prior soil moisture status affect the response of soil microbial community and function to extreme rain events in an arid area

Biological soil crusts (BSC) are an important multi-trophic component of arid ecosystems in the Mediterranean region, considered to have an important role in protecting the underlying soil from erosion and enhancing soil ecosystem functions. Using mesocosms in a 48 days glasshouse experiment, we investigated how previously hydrated (+W) and dried (-W) crust (+BSC) and uncrust (-BSC) -soil samples influenced microbial community structure, biomass and soil functionality of the underlying soils when exposed to two simulated extreme rain events. Community structure was assessed by phospholipid fatty acids analysis (PLFAs) and soil functionality by the activity of b-glucosidase, polyphenol oxidase, N-acetylglucosaminidase, acid phosphomoesterase and urease involve in C, P and N cycles. Crust increased the soil water content. In contrast, NH4 and NO3 were unaffected by the presence of the crust or its previous hydration status. N availability was affected by rain events; it declined from first to second event. Microbial biomasses were affected by the interaction crust x watering. Significant decline in biomasses was recorded in +BSC + W soils as a response to rain events. Little effects of treatments on soil enzymes were noticed; crust presence had a positive influence on the activity of phenol oxidase and a negative one on acid phosphomoesterase activity. The first rainfall had the greatest impact on microbial community structure, with communities in the previously hydrated crust affected most. These effects were less pronounced for the second rain event possibly due to microbial acclimation. Responses in enzyme profiles were consistent with those of communities, but delayed, with more marked responses following the second rainfall. We concluded that the effect of this lichen crust from the Mediterranean area on the response of soil microbial communities and enzymes to rainfall events depended strongly on the prior hydration status of the crust-soil complex.

Lichens Bite the Dust - A Bioweathering Scenario in the Atacama Desert.

SummaryBioweathering mediated by microorganisms plays a significant role in biogeochemical cycles on global scales over geological timescales. Single processes induced by specific taxa have been described but could rarely be demonstrated for complex communities that dominate whole landscapes. The recently discovered grit crust of the coastal Atacama Desert, which is a transitional community between a cryptogamic ground cover and a rock-bound lithic assemblage, offers the unique chance to elucidate various bioweathering processes that occur simultaneously. Here, we present a bioweathering scenario of this biocenosis including processes such as penetration of the lithomatrix, microbial responses to wet-dry cycles, alkalinolysis, enzyme activity, and mineral re-localization. Frequently occurring fog, for example, led to a volume increase of microorganisms and the lithomatrix. This, together with pH shifts and dust accumulation, consequently results in biophysical breakdown and the formation of a terrestrial protopedon, an initial stage of pedogenesis fueled by the grit crust.