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1.
In the desert areas of China investigated by the authors, various biological crusts were predominately associated with three blue-green algal (cyanobacterial) species, Microcoleus vaginatus Gom., Phormidium tenue (Menegh.) Gom. and Scytonema javanicum (Kütz.) Born et Flah. Their biomass and their compressive strength were measured simultaneously in the field in this study. It was also found that the compressive strength of algal crusts was enhanced with the increasing of algal biomass from an undetectable level to a value as high as 9.6 mg g−1 dry soil. However, when the algal biomass decreased, the compressive strength did not descend immediately, but remained relatively steady. The higher the algal biomass became, the thicker were the algal crusts formed. Given the same biomass, the highest compressive strength of man-made algal crusts in fields was found at an algal ratio of 62.5% M. vaginatus, 31.25% P. tenue and 6.25% S. javanicum, and it reached 0.89 kg cm−2. When the biomass of the crusts increased above the value of 8.16 mg chla g−1 dry soil, the compressive strength would not ascend easily. It indicated that the compressive strength of man-made algal crusts appeared temporarily saturated in the field.  相似文献   

2.
The influence of edaphic and orographic factors on the formation of algal diversity in biological soil crusts was studied in mountain tundras of the Polar and Subpolar Urals. Bare spots developed in the soils on different parent materials and overgrown to different extents were investigated. Overall, 221 algal species from six divisions were identified. Among them, eighty-eight taxa were new for the region studied. The Stigonema minutum, S. ocellatum, Nostoc commune, Gloeocapsopsis magma, Scytonema hofmannii, Leptolyngbya foveolarum, Pseudococcomyxa simplex, Sporotetras polydermatica species and species of the Cylindrocystis, Elliptochloris, Fischerella, Leptosira, Leptolyngbya, Myrmecia, Mesotaenium, Phormidium, Schizothrix genera were permanent components of biological soil crusts. The basis of the algal cenoses in soil crusts was composed of cosmopolitan cyanoprokaryotes, multicellular green algae with thickened covers and abundant mucus. The share of nitrogen fixers was high. The physicochemical properties of primary soils forming under the crusts of spots are described. The more important factors affecting the species composition of algae in the crusts are the elevation gradient, temperature, soil moisture, and the contents of Ca, Mg, mobile phosphorus, and total nitrogen.  相似文献   

3.
The research was carried out around dumps made at the beginning of twentieth century linked to Zn?CPb ore mining of deposits of Mississippi Valley type in Southern Poland. Soil algae communities were investigated near spoil dumps rich in Zn, Pb, Fe, Cd, and Tl. In algal crusts, Chlorophyta and Cyanophyta occur in filament forms such as Stichococcus bacillaris, Stichococcus chlorelloides, S. cf. fragilis, and Cylindrocapsa sp. The algal crusts form aggregates containing metal-bearing minerals and algal organic material. The development of the crusts occur on sandy-clayey soils poor in water and highly enriched in heavy metals (up to 68,800 mg kg?1 for Zn, 85,060 mg kg?1 for Pb, 369 mg kg?1 for Cd and 355 mg kg?1 for Tl). Algal-crust formation is an important initial stage which facilitates vascular plant succession and topsoil formation. The results of investigation of algal material with ESEM are presented and the mineral phases in the top soil layer based on the XRD and EDS are described. The results indicate the presence of secondary labile minerals of lead, e.g., anglesite and plumbojarosite and minerals of Zn, e.g., smithsonite and minrecordite.  相似文献   

4.
Biological soil crusts (BSCs) play an important role in the dune fixation and maintaining soil biota in arid desert systems. Free-living soil nematode communities could be used as significant bioindicators to reflect soil recover regime after sand burial. However, the relationship between BSCs and nematodes is rarely known. To examine the effects of BSCs on soil nematodes, 72 soil samples under cyanobacteria–lichen and moss crusts were collected to analyse nematode communities in the different aged vegetated areas at the southeastern edge of the Tengger Desert. Our results showed the colonization and development of BSCs significantly enhanced nematode diversity. Nematode abundances, generic richness, H′, MI, EI and SI were greater under crusts than those under noncrust. In particular, nematode abundances, generic richness, H′, MI, EI and SI were positively correlated with crust ages. The differences in nematode communities were also dependent upon crust types. Nematode abundances and generic richness under moss crusts were higher than those under cyanobacteria–lichen crusts. This can be contributed to the present and succession of BSCs that increased thickness of topsoil after dunes have been stabilized, namely, creating suitable habitats and providing an essential food source for nematodes.  相似文献   

5.
Nitrogen fixation in biological soil crusts from southeast Utah,USA   总被引：20，自引：0，他引：20  
Biological soil crusts can be the dominant source of N for arid land ecosystems. We measured potential N fixation rates biweekly for 2 years, using three types of soil crusts: (1) crusts whose directly counted cells were >98% Microcoleus vaginatus (light crusts); (2) crusts dominated by M. vaginatus, but with 20% or more of the directly counted cells represented by Nostoc commune and Scytonema myochrous (dark crusts); and (3) the soil lichen Collema sp. At all observation times, Collema had higher nitrogenase activity (NA) than dark crusts, which had higher NA than light crusts, indicating that species composition is critical when estimating N inputs. In addition, all three types of crusts generally responded in a similar fashion to climate conditions. Without precipitation within a week of collection, no NA was recorded, regardless of other conditions being favorable. Low (<1°C) and high (>26°C) temperatures precluded NA, even if soils were moist. If rain or snow melt had occurred 3 or less days before collection, NA levels were highly correlated with daily average temperatures of the previous 3 days (r2=0.93 for Collema crusts; r2=0.86 for dark crusts and r2=0.83 for light crusts) for temperatures between 1°C and 26°C. If a precipitation event followed a long dry period, NA levels were lower than if collection followed a time when soils were wet for extended periods (e.g., winter). Using a combination of data from a recording weather datalogger, time-domain reflectometry, manual dry-down curves, and N fixation rates at different temperatures, annual N input from the different crust types was estimated. Annual N input from dark crusts found at relatively undisturbed sites was estimated at 9 kg ha-1 year-1. With 20% cover of the N-fixing soil lichen Collema, inputs are estimated at 13 kg ha-1 year-1. N input from light crusts, generally indicating soil surface disturbance, was estimated at 1.4 kg ha-1 year-1. The rates in light crusts are expected to be highly variable, as disturbance history will determine cyanobacterial biomass and therefore N fixation rates.  相似文献   

6.
In order to estimate the biomass of photoautotrophic organisms in biological soil crusts (BSCs), based on the extraction and determination of phytoplanktonic chlorophyll-a (Chl-a) in aquatic ecosystems, this paper comparatively studied the Chl-a extraction efficiencies in ethanol, acetone, N, N -dimethyl -formamide (DMF) and dimethyl sulphoxide (DMSO) from algae, lichen, and moss crusts, analyzed the effects of dominant organisms or development degree of BSCs, mass of sample, and soil characteristics on the extraction efficiency. The results showed that the extraction efficiencies of different organic solvents were significantly different, and such efficiencies declined with the increase of mass of sample. DMSO resulted in the greatest extraction efficiency, but was not suitable for lichen crusts; DMF strongly underestimated the Chl-a content of man-made crusts relative to the other extractants, and was particularly affected by interfering pigments from the well-developed crusts. Generally, the extraction efficiency of ethanol was greater than that of acetone, and ethanol method showed the greatest stability compared with other 3 solvents. In addition, Chl-a content showed an increasing trend with the succession of BSCs when it was expressed on an areal basis. On the basis of this and related experiments we suggest Chl-a content of BSCs be extracted by ethanol and expressed on an areal basis.  相似文献   

7.
Biological soil crusts (BSC), most notably lichen crusts, develop and diversify in the Gurbantunggut Desert, the largest fixed and semi-fixed desert in China. Four different successional stages of BSC, including bare sand, microalgal crusts, lichen crusts, and moss crusts, were selected to determine successional changes in microalgal species composition and biomass and formation of BSC. A 10 × 10-m observation plot was established in an interdune region of the Gurbantunggut Desert and data were collected over an 8-year study period. The main results were: (1) different successional stages of BSC significantly affected the content of soil organic C and total and available N but not the total and available P and K content of soil; (2) composition of microalgal communities differed among the four successional stages; (3) significant differences in microalgal biomass were observed among the four successional stages; (4) bare sand was mainly uncompacted sand gains; (5) filamentous cyanobacteria, particularly Microcoleus vaginatus, were the dominant species in the early phase of crust succession. The presence of fungal mycelium and moss rhizoids prevented water and wind erosion.  相似文献   

8.
The objectives of this investigation in the HolyCross Mountain region of Poland were (1) to determineconcentration ranges and (2) mobility of elements within fivedetailed soil profiles and their apparent impact on thechemistry of some plant bioindicators, i.e. lichen thalli ofthe species Hypogymnia physodes (L.) Nyl. and Scotspine (Pinus sylvestris L.) bark. The results ofelemental determinations performed on soils and vegetationfrom the Holy Cross Mts show that some concentrations ofelements are elevated primarily due to air pollution.However, since 1994 a steady decrease in the content of S andsome heavy metals has been recorded in all the mediaexamined. Concentrations of many elements in H.physodes thalli and P. sylvestris needles of the Holy Cross Mountains are generally similarto those in other areas of Europe.  相似文献   

9.
Lichen phenolics that are known to leach out from lichen thalli during rainfall episodes are considered to be allelopathic or antimicrobial agents. On the other hand, small organic molecules originating from aboveground vegetation generally constitute an important C source for the soil microbial community. We studied the effects of leaching lichen acids on soil microbial processes by chemically removing usnic (UA) and perlatolic acid (PA) from the extracellular space of mat-forming lichen, Cladina stellaris, a dominant component of the ground vegetation in boreal oligotrophic forests. Removal of UA and PA did not affect the intracellular contents of the lichen. We hypothesized that if lichen acids have an adverse effect on soil biota, microbial respiration would increase underneath chemically manipulated lichen mats. In turn, if these substances provide energy source for the microorganisms, microbial respiration would decline under lichens from which PA and UA has been removed. Microbial metabolic activity, qCO2 was significantly lower under the lichens from which UA and PA had been removed, thus supporting the latter hypothesis. Removing UA and PA did not affect the amount of microbial C, N and P, or soil nutrient concentrations. Our results suggest that the microbial community in the soil under a lichen carpet is adapted to the presence of these lichen secondary metabolites and can utilize them as a C source. The approach of removing lichen substances from the system could be used as an effective research tool as it can overcome several problems that are often common in the studies on allelopathic interactions.  相似文献   

10.
Practical testing of the feasibility of cyanobacterial inoculation to speed up the recovery of biological soil crusts in the field was conducted in this experiment. Results showed that cyanobacterial and algal cover climbed up to 48.5% and a total of 14 cyanobacterial and algal species were identified at the termination of inoculation experiment; biological crusts' thickness, compressive and chlorophyll a content increased with inoculation time among 3 years; moss species appeared in the second year; cyanobacterial inoculation increased organic carbon and total nitrogen of the soil; total salt, calcium carbonate and electrical conductivity in the soil also increased after inoculation. Diverse vascular plant communities composed of 10 and 9 species are established by cyanobacterial inoculation on the windward and leeward surface of the dunes, respectively, after 3 years. The Simpson index for the above two communities are 0.842 and 0.852, while the Shannon-Weiner index are 2.097 and 2.053, respectively. In conclusion, we suggest that cyanobacterial inoculation would be a suitable and effective technique to recover biological soil crusts, and may further restore the ecological system.  相似文献   

11.
The formation of soil surface crusts leads to increased mechanical and hydraulic resistances. In this study, changes and relationships of both resistances under simulated sprinkle irrigation (or rainfall), and sprinkle followed by flooding, were examined. Results indicated that a silt-loam soil developed a thicker surface crust than a clay soil for any given kinetic energy (KE). Crusts as thick as 3.9 and 2.6 mm formed on the silt-loam and clay soils, respectively. Mechanical resistance, Rm, increased with increasing KE, where the effect was greater in the silt-loam and was attributed to intrinsic resistance and crust thickness. Steady-state infiltration rate (i) was much lower in crusted clay than crusted silt-loam soil. Changes of both Rm, and i closely followed changes in crust thickness (zc). Thicker crusts showed more resistance against external force than thinner crusts, due to more extended particle interlocking. Obtained functions indicated that the effect of thickness on strength was more significant in the lower range of crust thickness. The effect of zc on i strongly followed a negative power function for both soils, with higher i in the silt-loam soil.  相似文献   

12.

Purpose

Surface crusts are important features in arid desert areas and are critical to hydrological processes and ecosystem development. This paper aims to understand the effects of crusts on water movement in the soil and the factors that affect this and to provide the soil parameters for estimation of saturated hydraulic conductivity (K s) in ecohydrological models.

Materials and methods

The study area was located in the middle and lower reaches of the Heihe River Basin, an arid desert area in Northwest China. There were three crust types in this region: physical soil crusts (PSCs, formed by water drop and erosion), biological soil crusts (BSCs, formed by microorganisms, moss, algae, lichen, and soil materials), and salt soil crusts (SSCs, formed by soluble salts). The infiltration rates of different soil and crust types and scalped soils were determined in situ in the field conditions using a disc infiltrometer with three repetitions. Crusts and soils were collected, and their properties were determined in the laboratory.

Results and discussion

The K s of crust were significantly lower than that of scalped soils with a decrease of 13–70 %. The K s of crusts were related to the type of crust and the properties of soil beneath the crusts. In this region, the soil textures are similar throughout, due to ubiquitous loess sedimentation, so textural differences had no significant effect on K s. Soil organic matter (SOM) played a weak negative role on K s because most crusts had higher SOM than the underlying soil. However, both crust thickness and electrical conductivity (EC, an index of salt concentration) showed significantly negative exponential relationship with K s. Therefore, the SSC with high EC and thick crust have the lowest K s among all crust types. Because soil development is related to salt accumulation, structure, and crust formation, the K s follows the order of Solonchaks < Cambisols < Regosols, from lowest to highest.

Conclusions

Crusts have different characteristics compared with original soils and are the limiting layer of water infiltration in these arid soils. Therefore, the characteristics of crust must be considered in ecohydrological models. The main apparent controlling parameters of water infiltration rate in this area are crust thickness and EC.
  相似文献   

13.
Young thallus tissue of the epiphytic lichen, Parmelia sulcata, and surface soil associated with its host trees were collected on Mt. Amiata for analysis of metal content including Al, Fe, Mn, Cu, Zn and Hg. The purpose of this study was to achieve a better understanding of plant-soil Hg relationships by comparisons of the Mt. Amiata minesite with the summit of an active volcano — Mt. Etna — and thereby to gain more insight into metal source and eco-physiology as factors in plant-Hg distribution. Although an Hg source-plant distance relationship clearly exists on Mt. Amiata, its precise nature is still in doubt, as it was impossible to distinguish statistically at p<0.01 among linear, log-linear, exponential, and third order polynomial regressions, even with N=47. Nevertheless, the distance-from-source relationship for Hg was clearly unique. No significant pattern could be assigned to the other metals studied, nor was there evidence of a regular relationship between soil content and plant content except in the case of Hg. Parmelia from Mt. Amiata accumulates Hg from soil degassing which was not at all the case for its mercury source on Mt. Etna. The data also suggests that high Zn values in the lichen of Mt. Amiata may be based on long range atmospheric transport. The Zn content of Parmelia was not analyzed on Mt. Etna. Element atomic ratios, Fe/Al for example, provide good evidence for accumulation of surface soil particulates, other than cinnabar by the thallus. Finally, we conclude that widely separated populations of the same species can display biogeochemical differences that are best explained on an eco-physiological basis.  相似文献   

14.
Cyanobacterial-lichen soil crusts can be a dominant source of nitrogen for cold-desert ecosystems. Effects of surface disturbance from footprints, bike and vehicle tracks on the nitrogenase activity in these crusts was investigated. Surface disturbances reduced nitrogenase activity by 30–100%. Crusts dominated by the cyanobacterium Microcoleus vaginatus on sandy soils were the most susceptible to disruption; crusts on gypsiferous soils were the least susceptible. Crusts where the soil lichen Collema tenax was present showed less immediate effects; however, nitrogenase activity still declined over time. Levels of nitrogenase activity reduction were affected by the degree of soil disruption and whether sites were dominated by cyanobacteria with or without heterocysts. Consequently, anthropogenic surface disturbances may have serious implications for nitrogen budgets in these ecosystems.  相似文献   

15.
Biological soil crusts (BSCs) have important ecological functions in arid and semiarid lands, but they remain poorly understood in terms of the changes in microbial communities during BSC succession under in situ field conditions. Here, 454 pyrosequencing was used to assess the microbial community composition of four BSC types in the Tengger Desert of China: alga, lichen (cyanolichen and green alga-lichen), and moss crusts, representing early, middle, and final successional stages of BSCs, respectively. The results showed the highest diversity of microbial communities inhabiting lichen crusts, whereas the lowest diversity was observed in moss crusts. Five phyla, Proteobacteria, Actinobacteria, Cyanobacteria, Bacteroidetes, and Acidobacteria, accounted for about 72% to 87% of total prokaryotic sequences in different BSCs. The most abundant eukaryotic microorganism was Ascomycota, accounting for 47% to 93% of the total eukaryotic sequences. Along the succession of BSCs, the abundance of photoautotrophic Cyanobacteria, Chlorophyta, and Bacillariophyta declined, and that of heterotrophic microorganisms such as bacteria and fungi increased. Statistical analysis showed clear divergency of microbial taxa at the class level among the different successional stages of BSCs. The clustering results at class level showed that the moss crusts were the farthest from the rest in prokaryotic composition; the alga crusts were the most different in terms of eukaryotic microorganisms and the two kinds of lichen crusts were relatively closer in both compositions. Ordination analysis showed that the main variations of community structure among BSCs could be explained best by the abundance of Cyanobacteria and Ascomycota and by physiochemical properties of BSCs, including mechanical composition, moisture, and electrical conductivity. In conclusion, our results indicate that Cyanobacteria and Ascomycota likely play an important role in the evolution of BSC structure and functions and highlight the importance of environmental factors in shaping microbial community structures of BSCs in the Tengger Desert of China.  相似文献   

16.
Biological soil crusts (BSCs) cover up to 70% of the sparsely-vegetated areas in arid and semiarid regions throughout the world and play a vital role in dune stabilization in desert ecosystems. Soil enzyme activities could be used as significant bioindicators of soil recovery after sand burial. However, little is known about the relationship between BSCs and soil enzyme activities. The objective of this study was to determine whether BSCs could affect soil enzyme activities in revegetated areas of the Tengger Desert. The results showed that BSCs significantly promoted the activities of soil urease, invertase, catalase and dehydrogenase. The effects also varied with crust type and the elapsed time since sand dune stabilization. All the soil enzyme activities tested in this study were greater under moss crusts than under cyanobacteria–lichen crusts. The elapsed time since sand dune stabilization correlated positively with the four enzyme activities. The enzyme activities varied with soil depth and season, regardless of crust type. Cyanobacteria–lichen and moss crusts significantly enhanced all test enzyme activities in the 0–20 cm soil layer, but negatively correlated with soil depth. All four enzyme activities were greater in the summer and autumn than in spring and winter due to the vigorous growth of the crusts. Our study demonstrated that the colonization and development of BSCs could improve soil quality and promote soil recovery in degraded areas of the Tengger Desert.  相似文献   

17.
The cryptogamic soil crusts of the Great Basin Artemisia, Ceratoides, and Atriplex plant communities contain a significant heterotrophic N2-fixing microbial population in addition to the predominating filamentous cyanobacteria. The bacterial association with the cyanobacteria exhibits a phycosphere-like effect. Heterotrophically fixed N gains reached 17.5 μg N· g?1 of soil (23.1% increase above the initial soil N content) and 45.9 μg N·g?1 of soil (57.4% increase) after 3 and 5 weeks, respectively. (NH4)2SO4 and native plant material amendments to soil resulted in a 41–100% reduction in N2-fixation. The potential input of N to soil crusts may be reduced in the presence of shrub-produced allelochemic agents and by concurrent denitrification.  相似文献   

18.
A survey of the heavy metal content in a transplanted lichen Ramalina duriaei (De Not.) Bagl. was carried out in the region of an Israeli coal-fired power plant. Nickel, Cr, Cu, and Zn were analyzed in the lichen exposed to environmental influences for a period of 1 yr. The concentrations of metals were compared with the concentrations of the same metals measured in R. duriaei transplanted to the study area prior to the operation of the power plant. The results show that after the 1983–1984 period, the regional concentrations of Cr in the transplanted lichen thalli were found to be higher than in the lichen thalli transplanted to the same sites during the period February 1979-March 1980, prior to the operation of the coal-fired power plant. A regional decrease in Zn concentration in the lichen exposed during the latter period is probably linked to the decrease in the use of this metal as a constituent of foliar nutrients in agriculture. The regional increase of Cr in the 1983–1984 lichen material is probably connected with the operation of the Maor David coal-fired power plant located at Sharonim. A local increase in the Ni and Cr concentrations was found in the lichen transplanted to a nature reserve located north of the power station.  相似文献   

19.
Despite the critical role of biological soil crusts (BSCs) in arid and semi-arid ecosystem function, few studies are found concerning the most important environmental variables affecting their distribution and physiology. This study seeks to determine soil and microenvironmental factors affecting the spatial distribution and pigment production of BSC-forming lichens and mosses in open patches of a semi-arid Mediterranean kermes oak thicket. We measured late-successional BSC cover, shrub cover, distance to nearest kermes oak (to test for effects of kermes oak thicket microenvironment on BSC), and pigment concentration of one lichen (Cladonia foliacea) and one moss (Pleurochaete squarrosa) species in the Nature Reserve El Regajal-Mar de Ontígola (Central Spain). At the macroscale (>0.5 m), results showed that BSC distribution and pigments were tightly coupled to a suite of soil properties, in particular soil pH, Fe, and Ca. Specifically, soil pH had a positive relationship with the cover of five individual BSC-forming lichen species and was negatively related to pigment production in C. foliacea. When pH was excluded from the analysis, Ca appeared as the main soil variable and was correlated with total BSC cover and total lichen cover. The micronutrient Fe had a significant positive relationship with the concentration of eight pigments in P. squarrosa and was also coupled with the cover of two BSC-forming lichens. Manganese, previously proposed as a key limiting micronutrient for BSCs, affected lichen diversity in a negative way. At the microscale (∼0.5 m), kermes oak microenvironment, shrub cover, and moss cover were determinants of BSC distribution, and total lichen and total BSC cover were overrepresented on N and E-facing shrub microsites. Our findings suggest that soil chemical variability and microsite diversity created by neighbouring vegetation affect BSC distribution in complex and essential ways and that studies aiming to explore BSC-environment relationships should be conducted at various spatial scales. Studies based on species- or group-specific responses are, thus, inadequate to unveil the main factors determining the distribution of the diverse organisms that constitute BSCs and/or to propose potential tools aiming to restore BSC in arid and semiarid ecosystems.  相似文献   

20.
The movement of sand by erosion is a common feature of drylands during droughts and periods of sparse vascular plant cover. We examined the effects of sand deposition on the bioavailability of N in cyanobacterial-dominant soil crusts during and after a severe drought. Crusts were sampled from two depths on stony and stone-free surfaces with and without sandy deposits. All sites supported an extensive cover (up to 51%) of N-fixing cyanobacteria and cyanolichens. During drought, sand-covered crusts had up to three-times more mineral N (NH4+ and NO3−) and twice the mineralisable N, at both depths, than sand-free samples. Mineralisable N was always greater in the surface soil layer both during and after drought. During the drought, two common N-fixing cyanobacteria (Scytonema cf. hofman-bangii, Stigonema ocellatum) were significantly more abundant on uncovered than sand-covered surfaces. Increased N bioavailability likely results from autolysis and subsequent breakdown of N-enriched cyanobacterial cell material mediated by changes in the soil surface microenvironment. Our work suggests that landscape-level processes of sand deposition have a marked effect on soil nutrient pools by enhancing the accumulation of plant-available N on cyanobacterial crusted surfaces. Inappropriate land management or the loss of cyanobacterial soil crusts during drought would compromise the long-term bioavailability of soil N.  相似文献   

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