Geology topics

Yuanming Zhang

Publications and source records attributed to Yuanming Zhang.

6 recordsLinked to original sources

USGS2022

What is a biocrust? A refined, contemporary definition for a broadening research community

Studies of biological soil crusts (biocrusts) have proliferated over the last few decades. The biocrust literature has broadened, with more studies assessing and describing the function of a variety of biocrust communities in a broad range of biomes and habitats and across a large spectrum of disciplines, and also by the incorporation of biocrusts into global perspectives and biogeochemical models. As the number of biocrust researchers increases, along with the scope of soil communities defined as ‘biocrust’, it is worth asking whether we all share a clear, universal, and fully articulated definition of what constitutes a biocrust. In this review, we synthesize the literature with the views of new and experienced biocrust researchers, to provide a refined and fully elaborated definition of biocrusts. In doing so, we illustrate the ecological relevance and ecosystem services provided by them. We demonstrate that biocrusts are defined by four distinct elements: physical structure, functional characteristics, habitat, and taxonomic composition. We describe outgroups, which have some, but not all, of the characteristics necessary to be fully consistent with our definition and thus would not be considered biocrusts. We also summarize the wide variety of different types of communities that fall under our definition of biocrusts, in the process of highlighting their global distribution. Finally, we suggest the universal use of the Belnap, Büdel & Lange definition, with minor modifications: Biological soil crusts (biocrusts) result from an intimate association between soil particles and differing proportions of photoautotrophic (e.g. cyanobacteria , algae , lichens , bryophytes) and heterotrophic (e.g. bacteria , fungi , archaea) organisms , which live within , or immediately on top of , the uppermost millimetres of soil. Soil particles are aggregated through the presence and activity of these often extremotolerant biota that desiccate regularly , and the resultant living crust covers the surface of the ground as a coherent layer. With this detailed definition of biocrusts, illustrating their ecological functions and widespread distribution, we hope to stimulate interest in biocrust research and inform various stakeholders (e.g. land managers, land users) on their overall importance to ecosystem and Earth system functioning.

Biological Reviews↗

USGS2020

Practices of biological soil crust rehabilitation in China: Experiences and challenges

Biological soil crusts (biocrusts) are a central component of dryland ecosystems. However, they are highly vulnerable to disturbance and natural recovery may be slow. Therefore, finding ways to enhance the reestablishment of biocrusts after disturbance has been of great interest to researchers. This article provides a review of the laboratory cultivation and field inoculations of biocrust materials in China (mostly published in Chinese). Larger filamentous cyanobacteria (e.g. Microcoleus ) are relatively easy, although slow, to grow in culture compared to other biocrust components. Thus, most researchers have focused their efforts on the cyanobacteria and a few species of mosses that are also easily grown but at smaller scale. For all the studies, a small amount of biocrust material was collected and its biomass enhanced under controlled conditions. However, the enhancement was done using various methods and techniques in different regions. These materials were then applied to disturbed field sites, again with various methods. Results show that keeping the inoculated soil surface wet for some time period after inoculation was crucial for restoration success. Cyanobacterial establishment was improved by installing automatic sprinkling using micro‐irrigation techniques and/or physical structures that reduced sediment moving onto the inoculated area. Experimental applications in China showed that cyanobacteria can be successfully inoculated at a large scale (hundreds of ha). Moss inoculation, on the other hand, was only accomplished at a small scale (several m 2 ). To assess whether biocrust restoration can enhance the establishment of a self‐supporting ecosystem, further research is needed on how inoculation affects vegetation diversity and structure and ecological processes.

Restoration Ecology↗

USGS2019

Towards a predictive framework for biocrust mediation of plant performance: A meta‐analysis

Understanding the importance of biotic interactions in driving the distribution and abundance of species is a central goal of plant ecology. Early vascular plants likely colonized land occupied by biocrusts — photoautotrophic, surface‐dwelling soil communities comprised of cyanobacteria, bryophytes, lichens and fungi — suggesting biotic interactions between biocrusts and plants have been at play for some 2,000 million years. Today, biocrusts coexist with plants in dryland ecosystems worldwide, and have been shown to both facilitate or inhibit plant species performance depending on ecological context. Yet, the factors that drive the direction and magnitude of these effects remain largely unknown. We conducted a meta‐analysis of plant responses to biocrusts using a global dataset encompassing 1,004 studies from six continents. Meta‐analysis revealed there is no simple positive or negative effect of biocrusts on plants. Rather, plant responses differ by biocrust composition and plant species traits and vary across plant ontogeny. Moss‐dominated biocrusts facilitated, while lichen‐dominated biocrusts inhibited overall plant performance. Plant responses also varied among plant functional groups: C 4 grasses received greater benefits from biocrusts compared to C 3 grasses, and plants without N‐fixing symbionts responded more positively to biocrusts than plants with N‐fixing symbionts. Biocrusts decreased germination but facilitated growth of non‐native plant species. Synthesis . Results suggest that interspecific variation in plant responses to biocrusts, contingent on biocrust type, plant traits, and ontogeny can have strong impacts on plant species performance. These findings have important implications for understanding biocrust contributions to plant productivity and community assembly processes in ecosystems worldwide.

Journal of Ecology↗

USGS2018

Fungal loop transfer of nitrogen depends on biocrust constituents and nitrogen form

Besides performing multiple ecosystem services individually and collectively, biocrust constituents may also create biological networks connecting spatially and temporally distinct processes. In the fungal loop hypothesis rainfall variability allows fungi to act as conduits and reservoirs, translocating resources between soils and host plants. To evaluate the extent to which biocrust species composition and nitrogen (N) form influence loops, we created a minor, localized rainfall event containing 15 NH 4 + and 15 NO 3 − . We then measured the resulting δ 15 N in the surrounding dry cyanobacteria- and lichen-dominated crusts and grass, Achnatherum hymenoides , after 24 h. We also estimated the biomass of fungal constituents using quantitative PCR and characterized fungal communities by sequencing the 18S rRNA gene. We found evidence for the initiation of fungal loops in cyanobacteria-dominated crusts where 15 N, from 15 NH 4 + , moved 40 mm h −1 in biocrust soils with the δ 15 N of crusts decreasing as the radial distance from the water addition increased (linear mixed effects model (LMEM)): R 2 = 0.67, F 2,12 = 11, P = 0.002). In cyanobacteria crusts, δ 15 N, from 15 NH 4 + , was diluted as Ascomycota biomass increased (LMEM: R 2 = 0.63, F 2,8 = 6.8, P = 0.02), Ascomycota accounted for 82 % (±2.8) of all fungal sequences, and one order, Pleosporales, comprised 66 % (±6.9) of Ascomycota. The seeming lack of loops in moss-dominated crusts may stem from the relatively large moss biomass effectively absorbing and holding N from our minor wet deposition event. The substantial movement of 15 NH 4 + may indicate a fungal preference for the reduced N form during amino acid transformation and translocation. We found a marginally significant enrichment of δ 15 N in A. hymenoides leaves but only in cyanobacteria biocrusts translocating 15 N, offering evidence of links between biocrust constituents and higher plants. Our results suggest that minor rainfall events may initiate fungal loops potentially allowing constituents, like dark septate Pleosporales, to rapidly translocate N from NH 4 + over NO 3 − through biocrust networks.

Biogeosciences↗

USGS2016

Natural recovery of biological soil crusts after disturbance

Natural recovery of biological soil crusts (biocrusts) is influenced by a number of different parameters, such as climate, soil conditions, the severity of disturbance, and the timing of disturbance relative to the climatic conditions. In recent studies, it has been shown that recovery is often not linear, but a highly dynamic process directly influenced by non-linear external parameters as extraordinary climatic conditions (e.g., particularly dry or wet year). Natural recovery often follows a general succession pattern, starting out with cyanobacteria and algae, which is then followed by lichens and bryophytes at a later stage. However, this general sequence can be altered by parameters like dust deposition, fire effects, and special climatic conditions as in fog deserts and under mesic climates. Recent studies have proposed that under favorable, stable soil conditions, the initial soil-stabilizing cyanobacteria-dominated succession stages may be omitted and moss-dominated biocrusts can develop in the initial phases of biocrust development. During natural recovery of biocrusts, soil properties change, e.g., soil nutrient and organic matter contents increase. Also, silt and clay contents of encrusted soils increase with biocrust maturity, which may be caused by two mechanisms, i.e. entrapment of fine soil particles by biocrusts and the new formation of smaller particles by weathering of the existing substrate.

Book chapter↗

USGS2015

Growth responses of five desert plants as influenced by biological soil crusts from a temperate desert, China

In almost all dryland systems, biological soil crusts (biocrusts) coexist alongside herbaceous and woody vegetation, creating landscape mosaics of vegetated and biocrusted patches. Results from past studies on the interaction between biocrusts and vascular plants have been contradictory. In the Gurbantunggut desert, a large temperate desert in northwestern China, well-developed lichen-dominated crusts dominate the areas at the base and between the sand dunes. We examined the influence of these lichen-dominated biocrusts on the germination, growth, biomass accumulation, and elemental content of five common plants in this desert: two shrubs ( Haloxylon persicum , Ephedra distachya ) and three herbaceous plants ( Ceratocarpus arenarius , Malcolmia africana and Lappula semiglabra ) under greenhouse conditions. The influence of biocrusts on seed germination was species-specific. Biocrusts did not affect percent germination in plants with smooth seeds, but inhibited germination of seeds with appendages that reduced or eliminated contact with the soil surface or prevented seeds from slipping into soil cracks. Once seeds had germinated, biocrusts had different influences on growth of shrub and herbaceous plants. The presence of biocrusts increased concentrations of nitrogen but did not affect phosphorus or potassium in tissue of all tested species, while the uptake of the other tested nutrients was species-specific. Our study showed that biocrusts can serve as a biological filter during seed germination and also can influence growth and elemental uptake. Therefore, they may be an important trigger for determining desert plant diversity and community composition in deserts.

Ecological Research↗