Biological Soil Crust Cover Research Articles

Colonization of woodland species during restoration: seed or safe site limitation?

A strategy of assisted natural regeneration uses selective restoration interventions to remove potential barriers to passive natural regeneration and succession toward target ecosystems. In woodland restoration, this may involve the planting of woodland clusters that serve as seed sources for further colonization and/or site amelioration to enhance colonization and growth of the target species. We tested the importance of seed and safe site limitations for the colonization of birch and willows in experimental treatments representing a matrix of revegetation (+/−) and planted birch and willow clusters (+/−) on an eroded area in South Iceland. The revegetation was initiated in the fall of 1999 and clusters of birch and willows planted in 2002. Density of birch and willow seedlings and their distribution among microsites was surveyed in 2005, 2006, 2010, and 2015. Willow seedlings were first noted in 2006 but birch seedlings in 2010. In 2015, seedling density in revegetated plots with planted clusters was over 20 times greater than that of revegetated plots without clusters, indicating a strong seed limitation. No seedlings were found in plots that had not been revegetated, showing very strong microsite limitation. However, revegetation increased the cover of biological soil crust and other microsites favorable for seedling establishment. The results demonstrate that both seed and safe site limit the colonization of birch and willows, key species in woodland restoration, and highlight the importance of identifying barriers to spontaneous succession before selecting restoration strategies.

Recovery of biological soil crust richness and cover 12–16 years after wildfires in Idaho, USA

Abstract. Changing fire regimes in western North America may impact biological soil crust (BSC) communities that influence many ecosystem functions, such as soil stability and C and N cycling. However, longer-term effects of wildfire on BSC abundance, species richness, functional groups, and ecosystem functions after wildfire (i.e., BSC resilience) are still poorly understood. We sampled BSC lichen and bryophyte communities at four sites in Idaho, USA, within foothill steppe communities that included wildfires from 12 to 16 years old. We established six plots outside each burn perimeter and compared them with six plots of varying severity within each fire perimeter at each site. BSC cover was most strongly negatively impacted by wildfire at sites that had well-developed BSC communities in adjacent unburned plots. BSC species richness was estimated to be 65 % greater in unburned plots compared with burned plots, and fire effects did not vary among sites. In contrast, there was no evidence that vascular plant functional groups or fire severity (as measured by satellite metrics differenced normalized burn ratio (dNBR) or relativized differenced normalized burn ratio (RdNBR)) significantly affected longer-term BSC responses. Three large-statured BSC functional groups that may be important in controlling wind and water erosion (squamulose lichens, vagrant lichens, and tall turf mosses) exhibited a significant decrease in abundance in burned areas relative to adjacent unburned areas. The decreases in BSC cover and richness along with decreased abundance of several functional groups suggest that wildfire can negatively impact ecosystem function in these semiarid ecosystems for at least 1 to 2 decades. This is a concern given that increased fire frequency is predicted for the region due to exotic grass invasion and climate change.

Developing a predictive environment-based model for mapping biological soil crust patterns at the local scale in the Sahel

Several studies have demonstrated the great range of possibilities offered by remote sensing in identifying, estimating and mapping biological soil crust (BSC) patterns, i.e. a feature recognised to play major functions in drylands. However those techniques are suitable mainly where BSC patterns are abundant (>30%) and vegetation cover low (<10%), otherwise reflectance values matched different levels of BSCs mixed with vegetation and bare soil surfaces.This study developed an alternative methodology in mapping BSC presence in areas with a wide range of BSC cover associated with different mosaics encompassing vegetation and bare surfaces in the Sahel.Data were collected during intensive field surveys and remote sensing imagery of two typical Sahelian watersheds in western Niger (Banizoumbou and Tamou). Statistical methods were used to explore relationships between BSC occurrence and abundance and key environmental factors (rainfall, land use, land cover, vegetation, physical crusts).A predictive model of BSC spatial distribution was developed based on logistic regressions. This model allowed predicting and mapping BSC occurrence in areas where BSC cover ranged from 0 to 65% at Tamou (15% in average) and 1 to 48% at Banizoumbou (4% in average) and where vegetation cover ranged from <1% to >75%. Predicted values were obtained with an overall accuracy of 77.7% (kappa=0.54), classifying the model as good and discriminant.This work is the first step in assessing the local scale ecological functions of BSC. Further work is needed for extrapolation at the regional scale in order to provide a useful tool for ecological surveys and for predictions of soil surface dynamics related to global changes in dryland areas.

Biological soil crust cover is negatively related to vascular plant richness in Ozark sandstone glades

Abstract Sandstone glades in the Ozark highlands contain unique communities of vascular plants, including several species of conservation concern, as well as abundant communities of terricolous cryptogams—collectively termed biological soil crusts. Biological soil crusts have important ecological roles in grassland systems, such as preventing erosion and retaining soil moisture. Despite the conservation importance of sandstone glades, this ecosystem has received little scientific attention, and the drivers of plant diversity and soil crust prevalence in sandstone glades are poorly understood. In this study, we assessed relationships between soil crust cover and vascular plant species richness and tested whether dominance shifts from soil crusts to vascular plants along a soil gradient. Soil crust cover was negatively related to vascular plant species richness, and vascular plant richness increased (and crust cover decreased) with increasing soil organic matter. As soil organic matter increased, the propor...

模拟氮沉降对温带森林土壤酶活性的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 模拟氮沉降对温带森林土壤酶活性的影响 DOI: 10.5846/stxb201510232140 作者: 作者单位: 北京林业大学,北京林业大学 作者简介: 通讯作者: 中图分类号: 基金项目: 中央高校基本科研业务费专项资金（2016JX02）；国家自然科学基金（41373069） Effect of simulated nitrogen deposition on soil enzyme activities in a temperate forest Author: Affiliation: Beijing Forestry University,Beijing Forestry University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:森林土壤酶作为土壤中最活跃组分，能影响生态系统的物质循环过程，其活性能快速反映氮沉降对土壤环境的变化。以北京地带性植被辽东栎林为研究对象，利用模拟氮沉降方法，原位设计低氮（50 kg N hm-2 a-1，N50）、高氮（150 kg N hm-2 a-1，N150）两个施氮水平，每个施氮水平设置NaNO3、（NH4）2SO4、NH4NO3 3个不同的施氮类型，另设置空白对照（0 kg N hm-2 a-1，N0）。从时间格局上研究不同氮素化学形态和剂量对温带森林土壤6种酶（脲酶、酸性磷酸酶、碱性磷酸酶、β-葡萄糖苷酶、多酚氧化酶和过氧化氢酶）活性的影响。结果表明：在氮形态和水平的交互作用下，NH4NO3-N处理的脲酶活性显著高出NO3--N处理的24.20%（N50），NH4+-N处理对酸性磷酸酶活性的影响显著高出NO3--N处理的13.82%（N150）；在NH4+-N和NH4NO3-N处理中，N50水平下的脲酶活性分别高出N0处理的38.90%和24.20%，差异显著。对无氮形态和水平交互作用的酶活性分析得出，不同的施氮水平，对碱性磷酸酶和多酚氧化酶的酶活性有显著促进作用，碱性磷酸酶活性在N50和N150处理下分别比N0高20.2%和11.5%，N50和N150处理对多酚氧化酶活性的促进作用分别比N0处理高64.3%和41.8%，差异显著（P < 0.05）；NH4+-N处理对β-葡萄糖苷酶活性具有显著促进作用（P < 0.05），不同的施氮形态，对碱性磷酸酶、多酚氧化酶和过氧化氢酶的酶活性无显著影响。6种酶活性均呈现了显著的时间变化，氮添加对森林土壤酶活性的时间分异规律没有显著影响。此外，土壤微生物量碳、硝态氮和铵态氮含量与酶活性具有显著相关性（P < 0.05）。以上结果表明，氮添加通过改变森林土壤的环境因子，影响了土壤中的水解酶和氧化酶活性，进而改变了土壤有机碳库和养分循环。 Abstract:As one of the most active components of forest soil, soil enzymes contribute to the processes of soil organic matter decomposition and synthesis and influence all the biochemical reactions of soil, directly or indirectly. Human activities have dramatically increased the quantity of nitrogen fixed in terrestrial ecosystems, due to fossil fuel combustion, production and use of chemical fertilizers, and live stock ranching. Nitrogen (N) addition may rapidly influence soil carbon and nitrogen turnover during litter and soil organic matter (SOM) decomposition processes by changing the soil enzyme activities. Specifically, we hypothesized that adding N to N-limited ecosystems would increase the activity of hydrolytic enzymes and decrease that of oxidase. In the present study, we explored the effects of different forms and levels of nitrogen addition on extracellular enzyme activities in a temperate forest soil with dominant Quercus liaotungensis (light loam, mean annual temperature 11.7 ℃), in the Xi Mountain Forestry Station, China. Nitrogen loading was designed using three N forms (NO3--N, NH4+-N, and NH4NO3), each containing a low-N (50 kg N hm-2 a-1, N50) and high-N (150 kg N hm-2 a-1, N150) treatment plot; a treatment plot of 0 kg N hm-2 a-1 (N0) served as a control. Each treatment comprised three replicate plots of 10 m × 10 m on the forest floor, with each plot having similar vegetation and biological soil crust cover. Soil urease, acid phosphatase, alkaline phosphatase, β-glycosidase, polyphenol oxidase, and catalase activities were analyzed to investigate the impacts of N forms and levels on soil enzyme activities from the temporal pattern. The results showed a significant increase of NH4NO3-N treatment in soil urease activity (+24.20% upper NO3--N, N50), and NH4+-N treatment in acid phosphatase activity (+13.82% upper NO3--N, N150), and a considerable increase of N50 level in soil urease activity (+38.90% and +24.20% upper NH4+-N and NH4NO3 in N0, respectively) (P < 0.05). However, N forms and levels did not affect the activities of alkaline phosphatase, β-glycosidase, polyphenol oxidase, and catalase. Increasing N (N50 and N150) resulted in higher alkaline phosphatase activity (+20.2% and +11.5% upper N0, respectively) and polyphenol oxidase activity (+64.3% and +41.8% upper N0, respectively); and, with the increase in N addition, both the alkaline phosphatase and polyphenol oxidase activities increased at N50 addition, and decreased at N150. We observed a significant increase in β-glycosidase activity (P < 0.05) with the different forms of N addition (NH4+-N > NH4NO3-N > NO3--N), whereas N forms had no effect on alkaline phosphatase, polyphenol oxidase, and catalase activities. Furthermore, the highest activities of soil enzymes including urease, acid phosphatase, alkaline phosphatase, and polyphenol oxidase occurred in summer, but the highest β-glycosidase activity and the lowest catalase activity were found in the winter and autumn, respectively. However, N addition made little difference on temporal variation. Significant correlations of soil enzyme activities with soil microbial biomass carbon, NH4+-N, and NO3--N were established (P < 0.05). These results suggested that N deposition could affect the soil carbon and nutrient flow by influencing environmental factors and microbial enzymatic activities in temperate forest ecosystems. 参考文献 相似文献 引证文献

Long-Term Effects of Xerophytic Shrub Haloxylon ammodendron Plantations on Soil Properties and Vegetation Dynamics in Northwest China.

The xerophytic desert shrub Haloxylon ammodendron (C. A. Mey.) Bunge. is distributed naturally in Asian and African deserts, and is widely used for vegetation restoration in the desert regions of Northern China. However, there are limited long-term chrono-sequence studies on the impact of changed soil properties and vegetation dynamics following establishment of this shrub on mobile sand dunes. In Minqin County, Gansu Province, we investigated soil properties and herbaceous vegetation development of 10, 20, 30, 40, 50-year-old H. ammodendron plantations on mobile sand dunes. Soil sampling at two depths (0–5 and 5–20 cm) under the shrubs determined SOC, nutrition and soil physical characteristics. The results showed that: establishment of H. ammodendron had improved soil physio-chemical properties, increased thickness of soil crusts and coverage of biological soil crusts (BSCs), and promoted development of topsoil over an extended period of 5 decades. Soil texture and soil nutrition improved along the chrono-sequence according to three distinct phases: i) an initial fast development from 0 to 10 years, ii) a stabilizing phase from 10 to 30 years followed by iii) a relatively marked restoration development in 40 and 50-year-old plantations. Meanwhile, herbaceous community coverage also markedly increased in 30-year-old plantations. However, both soil and vegetation restoration were very slow due to low annual precipitation in Minqin county compared to other Northern China sand afforestation sites. Canonical Correspondence Analysis results demonstrated that herbaceous plant development was closely associated with changes in soil texture (increased clay and silt percentage) and availability of soil nutrients. Thus our results indicated that selection of the long-lived shrub H. ammodendron is an essential and effective tool in arid desert re-vegetation.

Biological soil crusts of Arctic Svalbard and of Livingston Island, Antarctica

Biological soil crusts (BSCs) occur in arid and semi-arid regions worldwide including the Polar Regions. They are important ecosystem engineers, and their composition and areal coverage should be understood before assessing key current functional questions such as their role in biogeochemical nutrient cycles and possible climate change scenarios. Our aim was to investigate the variability of BSCs from Arctic Svalbard and the Antarctic Island, Livingston, using vegetation surveys based on classification by functional group. An additional aim was to describe the structure of BSCs and represent a classification system that can be used in future studies to provide a fast and efficient way to define vegetation type and areal coverage. Firstly, this study demonstrates huge areas occupied by BSCs in Arctic Svalbard, with up to 90 % of soil surface covered, dominated by bryophytes and cyanobacteria, and showing an unexpectedly high variability in many areas. Livingston Island has lower percentage coverage, up to 55 %, but is dominated by lichens. Our findings show that both Polar Regions have varied BSC coverage, within the sites and between them, especially considering their harsh climates and latitudinal positions. Secondly, we have classified the BSCs of both areas into a system that describes the dominant functional groups and local geography, creating a simple scheme that allows easy identification of the prevailing vegetation type. Our results represent the first contribution to the description of BSCs based on their functional group composition in Polar Regions.

Factors driving species assemblage in Mediterranean soil seed banks: from the large to the fine scale.

Many studies have analysed the mechanisms that determine plant coexistence in standing vegetation, but the determinants of soil seed bank species assemblies have rarely been studied. In gypsum soil communities, aerial vegetation and seed banks are tightly connected in space and time, but the mechanisms involved in their organization may differ. The aim of this study is to understand the relative importance of biotic and abiotic factors controlling soil seed bank composition and structure. Persistent and complete (i.e. persistent plus transient) soil seed banks were investigated at two spatial scales in a very species-rich semi-arid community dominated by annuals. A water addition treatment equivalent to 50 % annual increase in average precipitation (abiotic factor) was applied for two consecutive years, and the relationships of the soil seed bank to the biological soil crust (BSC), above-ground vegetation and the presence of Stipa tenacissima tussocks (biotic factors) were simultaneously evaluated. As expected, the standing vegetation was tightly related to seed abundance, species richness and composition in both seed banks. Remarkably, BSC cover was linked to a decrease in seed abundance and species richness in the persistent seed bank, and it even determined complete seed bank composition at the fine spatial scale. However, this effect disappeared at coarser scales, probably because of the high spatial heterogeneity induced by BSCs. In contrast to findings on standing vegetation, Stipa and the irrigation treatment for two consecutive years had no effect on soil seed banks. Soil seed bank assemblies in our semi-arid plant community were the result of above-ground vegetation dynamics and of the direct filtering processes on seed fate operated by the spatially heterogeneous BSCs. Cover of BSCs was negatively correlated with seed abundance and species richness, and affected seed species composition in the soil. Changes in species composition and enrichment when the BSC cover is low suggest that BSCs promote a fine scale niche differentiation in the soil seed bank and thereby potentially enhance species coexistence and high species diversity in these communities.

Effects of Intermediate-Term Grazing Rest on Sagebrush Communities with Depleted Understories: Evidence of a Threshold

Millions of hectares of sagebrush (Artemisia L.) plant communities have been degraded by past improper management, resulting in dense sagebrush stands with depleted herbaceous understories. Rest from grazing is often applied to promote recovery. However, the effect of intermediate-term (5–10 years) rest from grazing in sagebrush communities with depleted herbaceous understories and dense sagebrush is relatively unknown. We compared well-managed, moderate grazing (grazed) with intermediate-term (5 and 6 years) rest (ungrazed) at five sites in southeastern Oregon. Sites were Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis Beetle & Young) communities with dense sagebrush and depleted herbaceous understories. Perennial herbaceous cover was greater in ungrazed compared with grazed areas, but this was expected because herbivory removes foliar vegetation tissue (i.e., cover). Density of herbaceous vegetation, diversity, and species richness did not differ between ungrazed and grazed areas. Similarly, bare ground, litter, and biological soil crust cover did not differ between treatments. These results suggest that intermediate-term rest is unlikely to elicit recovery of the understory compared with moderate grazing in these communities. The results of this study also suggest that degraded Wyoming big sagebrush communities likely have crossed a threshold that may be difficult to reverse.

A review of the ecology, ecophysiology and biodiversity of microalgae in Arctic soil crusts

Biological soil crusts have been extensively studied in arid lands of temperate regions, particularly semi-arid steppes and warm deserts. Arctic soil crusts have received some attention, but they are far less studied than their temperate counterparts. While the tundra zone of Arctic regions has an abundant cover of lichens, mosses and low-growing vascular plants, the High Arctic semi-arid and arid deserts have a much reduced but still very significant cover of biological soil crust dominated by microalgae. This review discusses what is known about Arctic soil crusts with the intention of stimulating study of this sensitive ecosystem. Arctic soil crusts are considered to be one of the most extreme habitat types on earth. Low temperatures and lack of water associated with a wide spectrum of disturbances have a dramatic effect on chemical and physical soil ecological properties (salinity, pH, conductivity and gas content). Microalgae are the keystone microbial species in polar crusts, being significant primary producers, fixing atmospheric nitrogen and secreting polysaccharides that bind soil aggregates together, thereby reducing erosion and water runoff. The biological diversity of soil crust microalgae in the Arctic is high. Soil crusts of the Arctic semi-arid and arid deserts provide a special opportunity to study the environmental factors controlling the diversity, distribution and abundance of the microalgae in the absence of anthropogenic disturbance. However, anthropogenic disturbances and climate change are occurring in the Arctic, and even more transformations are expected in the near future. Therefore, the ecological study of Arctic ecosystems, including biological soil crusts, is a matter of urgency.

Annual grass invasion in sagebrush steppe: the relative importance of climate, soil properties and biotic interactions.

The invasion by winter-annual grasses (AGs) such as Bromus tectorum into sagebrush steppe throughout the western USA is a classic example of a biological invasion with multiple, interacting climate, soil and biotic factors driving the invasion, although few studies have examined all components together. Across a 6000-km(2) area of the northern Great Basin, we conducted a field assessment of 100 climate, soil, and biotic (functional group abundances, diversity) factors at each of 90 sites that spanned an invasion gradient ranging from 0 to 100% AG cover. We first determined which biotic and abiotic factors had the strongest correlative relationships with AGs and each resident functional group. We then used regression and structural equation modeling to explore how multiple ecological factors interact to influence AG abundance. Among biotic interactions, we observed negative relationships between AGs and biodiversity, perennial grass cover, resident species richness, biological soil crust cover and shrub density, whereas perennial and annual forb cover, tree cover and soil microbial biomass had no direct linkage to AG. Among abiotic factors, AG cover was strongly related to climate (increasing cover with increasing temperatureand aridity), but had weak relationships with soil factors. Our structural equation model showed negative effects of perennial grasses and biodiversity on AG cover while integrating the negative effects of warmer climate and positive influence of belowground processes on resident functional groups. Our findings illustrate the relative importance of biotic interactions and climate on invasive abundance, while soil properties appear to have stronger relationships with resident biota than with invasives.

Analysis of Changes in Biological Soil Crusts Using Landsat Image Time Series for the Southern California Desert

Developers of renewable energy installations in Southern California must monitor the impacts of operations of new facilities on fragile desert ecosystems. This study is the first to use Landsat satellite spectral data to map changes in the distribution of biological soil crusts (BSCs) across federal lands of the Lower Colorado Desert. The coverage of BSCs comprising >33% pixel area totaled 4008 Km2 in 1990, and increased to 4841 Km2 by 2014. The proximity of changing areas of BSC cover between 1990 and 2014 to known river flow channels such as the Lower McCoy Wash, Riverside County, CA) implied that flash floods associated with heavy precipitation events are important agents of change for BSC cover. These results have an immediate application for mapping the potential impacts of flash flood events around developed urban areas and utility-scale solar energy installations in the deserts of Southern California.

Effects of biological soil crust and water availability on seedlings of three perennial Patagonian species

Biological soil crusts are communities composed of mosses, lichens and cyanobacteria. They cover a large portion of the arid and semiarid regions of the world and play key roles in nutrient cycles and soil erosion diminution. Biological soil crust might affect germination, establishment and growth of vascular plants. In this study we examined the differential response to soil cover and water availability of grasses and shrubs. Our hypothesis was that seed germination and seedling survival are greater in soils with biological soil crust cover because crust have positive effects on vascular plant establishment. We evaluated the effect of biological soil crust cover on seed emergence, survival and seedling growth of Nassella tenuis, Senecio subulatus and Larrea divaricata. The experiment had four treatments combining biological soil crust (C) or bare soil (BS) with drought (D) or soil at field capacity (FC). Seeds of L. divaricata did not germinate and S. subulatus only germinated in BS-FC. Emergence and biomass of seedlings of N. tenuis were higher with C and at FC. There were no differences in seedling survival. Soil cover with biological soil crust and water availability influenced germination and seedling growth and their effects are different according to the species or plant functional groups. Germination of seeds varies with the composition and structure of the biological soil crust and the vascular plants, and the response may change with different species or plant functional groups.

Effects of Re-vegetation on Herbaceous Species Composition and Biological Soil Crusts Development in a Coal Mine Dumping Site.

Despite the critical roles of plant species' diversity and biological soil crusts (BSCs) in arid and semi-arid ecosystems, the restoration of the diversity of herbaceous species and BSCs are rarely discussed during the process of vegetation restoration of anthropogenically damaged areas in these regions. In this study, the herbaceous plant species composition, along with the BSCs coverage and thicknesses, was investigated at six different re-vegetation type sites, and the natural vegetation site of the Heidaigou open pit coal mine in China's Inner Mongolia Autonomous Region was used as a reference. The highest total species richness (16), as well as the species richness (4.4), occurred in the Tree and Herbaceous vegetation type site. The species composition similarities between the restored sites and the reference site were shown to be very low, and ranged from 0.09 to 0.42. Also, among the restored sites, the similarities of the species were fairly high and similar, and ranged from 0.45 to 0.93. The density and height of the re-vegetated woody plants were significantly correlated with the indexes of the diversity of the species. The Shrub vegetation type site showed the greatest total coverage (80%) of BSCs and algae crust coverage (48%). The Shrub and Herbaceous type had the greatest thicknesses of BSCs, with as much as 3.06 mm observed, which was followed by 2.64 mm for the Shrub type. There was a significant correlation observed between the coverage of the total BSCs, and the total vegetation and herbaceous vegetation coverage, as well as between the algae crust coverage and the herbaceous vegetation coverage. It has been suggested that the re-vegetated dwarf woody plant species (such as shrubs and semi-shrubs) should be chosen for the optimal methods of the restoration of herbaceous species diversity at dumping sites, and these should be planted with low density. Furthermore, the effects of vegetation coverage on the colonization and development the BSCs should be considered in order to reconstruct the vegetation in disturbed environments, such as mine dumpsites in arid areas.

Multiscale effects on biological soil crusts cover and spatial distribution in the Monte Desert

Biological soil crusts (BSC) play diverse roles in arid and semi-arid ecosystems such as increasing soil fertility and reducing soil loss due to aeolian and hydric erosion, but they are very sensitive to disturbances. These attributes point to the relevance of BSC for soil conservation and restoration. In order to use BSC for restoration of degraded soils, we need to understand the ecological drivers of BSC. In this study, we analyzed the effect of environmental factors on BSC cover at different spatial scales in the central Monte Desert (Argentina), including landform, slope, aspect, vascular plants, and disturbance intensity. We evaluated the effects of different factors with linear mixed effect models, comparing the adjustment of models of different complexity, which included different number of factors. First, at the landscape scale, we analyzed BSC cover in two geomorphological units with different soils, topography, and vegetation. BSC cover was higher in the old riverbed, which has a higher proportion of fine clay soil particles, than in the aeolian plain. Disturbance effects were apparent in the old riverbed, showing increasing BSC cover at higher distances from settlements, and BSC located both, under and outside plant canopies. At the mesoscale, we found no differences of BSC cover in dune flanks and inter-dune valleys of the aeolian plain. Finally, at the microscale, BSC patches of higher surface cover were found in association with vascular plants (Larrea divaricata, Bulnesia retama, Lycium sp.), on mounds, and in microsites of southern exposure and high slopes. Our findings suggest that BSC develop preferentially associated with vascular plants, which generate mounds and sloped microsites with southern exposure, where lower irradiances reduce desiccation in these extremely dry environments.

Cross-scale interactions between surface components and rainfall properties. Non-linearities in the hydrological and erosive behavior of semiarid catchments

• Semiarid catchments with BSCs showed a sharp threshold in runoff generation. • The threshold in runoff generation is controlled by total rainfall amount. • In low magnitude rains, runoff generated in BSCs areas is reinfiltrated in vegetation. • In high magnitude events, vegetation is unable of infiltrate all runoff from BSCs areas. • In these events, runoff connectivity is increased, but no extra sediments were exported. Non-vegetated areas in arid and semiarid ecosystems are usually covered by biological soil crusts (BSCs), which modify many surface properties and reduce soil erosion at local spatial scales. Nevertheless, runoff generated in these areas could increase downstream erosion, or on the contrary, supply water to downslope plants, which act as surface obstructions slowing down runoff, trapping sediments and thus reducing water erosion. However, their buffer capacity might be overwhelmed during some torrential rains, increasing catchment connectivity and modifying the hydrological behavior and subsequent water erosion measured at the catchment outlet. To progress in the knowledge of the effect of the interactions between BSCs and vegetation on runoff generation and water erosion at catchment scale, the long term hydrological response of semiarid badlands with an important cover of BSCs has been studied. This effect has been analyzed using piecewise regression analysis to find any possible break point in the runoff response of the catchment to rainfall, attributable to variations in the hydrological connectivity of the catchment. Once we found this break point, we used it to divide the database in two sub-databases, and we built two structural equation models (SEM) to identify the main hydrological drivers controlling runoff generation and water erosion at sub-datasets, corresponding with different stages of catchment connection. Our results show that during low magnitude rainfall events, runoff and erosion measured at the catchment outlet come essentially from physically crusted areas directly connected to the channel network and are controlled by rainfall intensity, whereas runoff generated in areas with BSCs is reinfiltrated downstream into local vegetation patches. However, during high-magnitude events, vegetated buffers are saturated, connecting areas covered by BSCs with the channel network and increasing the catchment efficiency in exporting water out of the system. Nevertheless, water and sediments connectivity is not always linked, and most sediments measured during both low and high-magnitude events are almost exclusively supplied by physically crusted areas, whereas, BSCs areas rarely yield sediments. The differences in the hydrological behavior of the catchment under low and high-magnitude rainfall events were found to be controlled by the interactions between source and vegetated areas, which in last turn control the hydrological connectivity at catchment scale.

Effects of artificially cultivated biological soil crusts on soil nutrients and biological activities in the Loess Plateau

Biological soil crusts (BSCs) play an important role in the early succession of vegetation restoration in the Loess Plateau, China. To evaluate the effects of artificially cultivated BSCs on the soil surface micro-environment, we obtained natural moss crusts and moss-lichen crusts from the Loess Plateau of Shaanxi province, and subsequently inoculated and cultivated on horizontal and sloping surfaces of loess soil in a greenhouse. The chemical and biological properties of the subsoil under cultivated BSCs were determined after 10 weeks of cultivation. The results indicated that BSCs coverage was more than 65% after 10 weeks of cultivation. Moss crust coverage reached 40% after 5 weeks of cultivation. Compared with the control, soil organic matter and available nitrogen contents in moss crust with the horizontal treatments increased by 100.87% and 48.23%, respectively; increased by 67.56% and 52.17% with the sloping treatments, respectively; they also increased in moss-lichen crust with horizontal and sloping treatments, but there was no significant difference. Available phosphorus in cultivated BSCs was reduced, soil pH was lower and cationic exchange capacity was higher in cultivated BSCs than in the control. Alkaline phosphatase, urease and invertase activities were increased in artificially cultivated BSCs, and alkaline phosphatase activity in all cultivated BSCs was obviously higher than that in the control. Numbers of soil bacteria, fungi and actinomycetes were increased in the formation process of cultivated BSCs. These results indicate that BSCs could be formed rapidly in short-term cultivation and improve the micro-environment of soil surface, which provides a scientific reference for vegetation restoration and ecological reconstruction in the Loess Plateau, China.

Identification of Factors Influencing the Restoration of Cyanobacteria-Dominated Biological Soil Crusts

Biological soil crusts (BSCs) cover >35% of the Earth’s land area and contribute to important ecological functions in arid and semiarid ecosystems, including erosion reduction, hydrological cycling, and nutrient cycling. Artificial rapid cultivation of BSCs can provide a novel alternative to traditional biological methods for controlling soil and water loss such as the planting of trees, shrubs, and grasses. At present, little is known regarding the cultivation of BSCs in the field due to lack of knowledge regarding the influencing factors that control BSCs growth. Thus, we determined the effects of various environmental factors (shade; watering; N, P, K, and Ca concentrations) on the growth of cyanobacteria-dominated BSCs from the Sonoran Desert in the southwestern United States. The soil surface changes and chlorophyll a concentrations were used as proxies of BSC growth and development. After 4 months, five factors were found to impact BSC growth with the following order of importance: NH4NO3 ≈ watering frequency>shading>CaCO3 ≈ KH2PO4. The soil water content was the primary positive factor affecting BSC growth, and BSCs that were watered every 5 days harbored greater biomass than those watered every 10 days. Groups that received NH4NO3 consistently exhibited poor growth, suggesting that fixed N amendment may suppress BSC growth. The effect of shading on the BSC biomass was inconsistent and depended on many factors including the soil water content and availability of nutrients. KH2PO4 and CaCO3 had nonsignificant effects on BSC growth. Collectively, our results indicate that the rapid restoration of BSCs can be controlled and realized by artificial “broadcasting” cultivation through the optimization of environmental factors.

Advanced image processing methods as a tool to map and quantify different types of biological soil crust

Biological soil crusts (BSCs) modify numerous soil surface properties and affect many key ecosystem processes. As BSCs are considered one of the most important components of semiarid ecosystems, accurate characterisation of their spatial distribution is increasingly in demand. This paper describes a novel methodology for identifying the areas dominated by different types of BSCs and quantifying their relative cover at subpixel scale in a semiarid ecosystem of SE Spain. The approach consists of two consecutive steps: (i) First, Support Vector Machine (SVM) classification to identify the main ground units, dominated by homogenous surface cover (bare soil, cyanobacteria BSC, lichen BSC, green and dry vegetation), which are of strong ecological relevance. (ii) Spectral mixture analysis (SMA) of the ground units to quantify the proportion of each type of surface cover within each pixel, to correctly characterize the complex spatial heterogeneity inherent to semiarid ecosystems. SVM classification showed very good results with a Kappa coefficient of 0.93%, discriminating among areas dominated by bare soil, cyanobacteria BSC, lichen BSC, green and dry vegetation. Subpixel relative abundance images achieved relatively high accuracy for both types of BSCs (about 80%), whereas general overestimation of vegetation was observed. Our results open the possibility of introducing the effect of presence and of relative cover of BSCs in spatially distributed hydrological and ecological models, and assessment and monitoring aimed at reducing degradation in these areas.

Plant interactions with changes in coverage of biological soil crusts and water regime in Mu Us Sandland, China.

Plant interactions greatly affect plant community structure. Dryland ecosystems are characterized by low amounts of unpredictable precipitation as well as by often having biological soil crusts (BSCs) on the soil surface. In dryland plant communities, plants interact mostly as they compete for water resources, and the direction and intensity of plant interaction varies as a function of the temporal fluctuation in water availability. Since BSCs influence water redistribution to some extent, a greenhouse experiment was conducted to test the hypothesis that the intensity and direction of plant interactions in a dryland plant community can be modified by BSCs. In the experiment, 14 combinations of four plant species (Artemisia ordosica, Artemisia sphaerocephala, Chloris virgata and Setaria viridis) were subjected to three levels of coverage of BSCs and three levels of water supply. The results show that: 1) BSCs affected plant interaction intensity for the four plant species: a 100% coverage of BSCs significantly reduced the intensity of competition between neighboring plants, while it was highest with a 50% coverage of BSCs in combination with the target species of A. sphaerocephala and C. virgata; 2) effects of the coverage of BSCs on plant interactions were modified by water regime when the target species were C. virgata and S. viridis; 3) plant interactions were species-specific. In conclusion, the percent coverage of BSCs affected plant interactions, and the effects were species-specific and could be modified by water regimes. Further studies should focus on effects of the coverage of BSCs on plant-soil hydrological processes.