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Biological soil crusts (BSCs) are ubiquitous communities of diminutive organisms such as cyanobacteria, green algae, lichens, mosses and others associated closely with particles of surface soil, forming a cohesive thin horizontal layer. The ecological roles of BSCs affecting soil nutrient cycling, stability and hydrological processes, infl uencing the germination and establishment of vascular plants, and serving as habitats for numerous arthropods and microorganism have been well documented. We tested the hypothesis that micro-geomorphological features determine the spatial distribution of BSCs by reallocating related abiotic resources at small-and medium-scales in the Tengger Desert. Our results showed that higher soil pH and higher total potassium content in topsoil positively correlated with the colonization of cyanobacteria and algae in the earliest successional stages of BSCs, while increasing dust deposition onto the topsoil enhanced the development of lichen and mosses in the later stages of BSCs. Increasing soil moisture raised the proportion of mosses and lichen in BSCs, this will possibly change the ecological functions of BSCs, such as nitrogen-fi xation by cyanobacteria, due to the conversion from a complex to relative simple type of BSC. Micro-geomorphology has created various habitats at a small-scale affecting colonization and development of cryptogams. This paper considers the contribution of micro-geomorphology to biodiversity in the extreme arid desert systems.

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The presence of biological soil crusts can affect the germination and survival of vascular plants, but the reasons are not well investigated. We have conducted a field investigation and greenhouse experiments to test the effect of crusts on two desert annual plants, which occur on the stabilized dunes of the Tengger Desert in N China. The results showed that biological soil crusts negatively influenced the seed bank of Eragrostis poaeoides and Bassia dasyphylla. The important effect of biological soil crusts on seed germination and establishment were performed indirectly through reducing the amount of germinating seeds. Field investigation and experimental results with regard to the seed bank indicated that higher seedling density was found in disturbed crust soil and bare soil surface than in intact crust soils. Greenhouse experiments showed that the effects of biological soil crusts on germination and establishment of the two plants are not obvious in moist condition, while disturbed crusts are more favorable to seed germination in dry treatment. Significant differences in biomass were found between disturbed crust soil and bare soil. Survival and growth of the two annual plants were enhanced in both algal and moss crusts during the season of rainfall or in moist environment, but crusts did not affect seedling survival in the dry period. The small seeded E. poaeoides has higher germination than larger-seeded B. dasyphylla in crust soils, but B. dasyphylla has a relatively higher survival rate than E. poaeoides in crust soils.

Recently published green infrastructure, nature-based solutions, and ecosystem disservices (ED) literature have focused primarily on the supply of urban regulating and cultural ecosystem services (ES). Other literature on urban and peri-urban agriculture has mostly studied the role of localized, intensive agricultural practices in providing food to inhabitants. The aim of this review is to raise awareness and stress the knowledge gap on the importance of urban provisioning ES, particularly when implementing an edible green infrastructure (EGI) approach as it can offer improved resilience and quality of life in cities. We compiled and systematically analyzed studies on urban ES and ED related to a number of EGI typologies. Our systematic review of the relevant literature via an EGI framework, identified more than 80 peer-reviewed publications that focused on ES and food production in urban areas. An EGI approach can contribute socially, economically, and environmentally to urban sustainability and food security. However, such benefits must be weighed against ED trade-offs, including: potential health risks caused by human exposure to heavy metals and organic chemical contaminants often present in urban surroundings. We conclude with recommendations and guidelines for incorporating EGI into urban planning and design, and discuss novel areas for future research. 1. NBS is an approach that improves upon the livability and resilience of cities in retrospect to climate change. Although these concepts are apparently used interchangeably, below we refer to urban GI as hybrid infrastructure of green and built systems (e.g. urban forests, wetlands, parks, green roofs, and walls that together can contribute to ecosystem resilience) and human benefits through their ecological processes or ES (Demuzere et al., 2014; Russo et al., 2016). These benefits or ES are also referred to as NBS when GI is incorporated into urban management, planning, design, and sociopolitical practices and policies for climate change mitigation and adaptation. Indeed, urban GI has been found to contribute positively to outdoor and indoor environments (Russo et al., 2016; Wang et al., 2014), while providing many relevant ES − including important health benefits (Coutts and Hahn, 2015). As such, GI delivers measurable ES and benefits that are fundamental to the concept of a sustainable city (Ahern et al., 2014). Urban and peri-urban agriculture and forestry (UPAF), on the other hand have been studied and can be considered a set of experiences and practices for implementing the GI approach in and around cities (Eigenbrod and Gruda, 2015; Escobedo et al., 2011). UPAF systems focus on agro-forestry production and agro-ecological practices (e.g. production of vegetables, mushrooms, fruits, crops, aromatic and medicinal herbs, and ornamental plants) as well as the raising of animals (e.g. livestock and aquaculture) in and around urban areas (FAO, 2016). Whereas GI, as stated earlier, is closely related to ES and human wellbeing, with particular focus on regu...

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