Feasibility of cyanobacterial inoculation for biological soil crusts formation in desert area

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.     

Responses of Crops to Soil Salinization in South Baja California,Mexico

Soil salinization has become a serious problem all over the world. In this study, the influence of salinity of irrigation water and soil on plant nutrition and physiological disorders were investigated. The study was conducted in three agricultural fields in South Baja California, Mexico where saline stress of crops by soil salinization has become a serious problem under the arid climate.

There was a significant correlation (P < 0.05) between sodium (Na) concentration and electrical conductivity (EC) of the water. The soil pH was extremely high in all areas, and the Na concentration was higher than that of other elements. In spite of the salinized water and soil, vegetables did not show symptoms of nutritional disorders. Unlike the vegetables, fruit leaves showed symptoms of nutritional disorders. There was not a correlation between the concentration ratio (CR) of elements of the leaves, which showed symptoms to healthy leaves in a same tree, and the visible symptoms of the nutritional disorder.     

铜尾矿生物结皮的生物固氮及其影响因素研究

在铜尾矿生态系统自然恢复过程中,生物结皮广泛存在并成为尾矿生态系统演替早期的重要阶段。本文采用乙炔原位还原法对藻类结皮、藻藓混合结皮和藓类结皮的生物固氮特征进行了系统研究。结果表明:(1)生物结皮显著提高了铜尾矿总氮含量,同时降低了铜的含量。(2)不同类型生物结皮的固氮能力差别较大,其中藻藓混合结皮的生物固氮量最高,在N 4.36～30.39 kg hm2 a–1之间;藻类结皮和藓类结皮的固氮量分别为N 1.32～8.78、0～16.34 kg hm2 a–1。(3)生物固氮能力随季节变化明显,夏季的生物固氮量最高,春季次之,秋冬季节相对较低。(4)铜尾矿基质pH、NH4+-N和水溶性有机碳(WSOC)等与生物固氮量呈显著正相关(p<0.05),而土壤容重、NO3--N和总铜等与生物固氮量呈显著负相关(p<0.05)。     

Spring dynamics of soil carbon, nitrogen, and microbial activity in earthworm middens in a no-till cornfield

Earthworm activity may be an important cause of spatial and temporal heterogeneity of soil properties in agroecosystems. Structures known as “earthworm middens,” formed at the soil surface by the feeding and casting activities of some earthworms, may contribute significantly to this heterogeneity. We compared the temporal dynamics of carbon (C), nitrogen (N), and microbial acitivity in Lumbricus terrestris middens and in surrounding non-midden (bulk) soil during the spring, when seasonal earthworm activity was high. We sampled soil from middens and bulk soil in a no-till cornfield on four dates during May and June 1995. Soil water content and the weight of coarse organic litter (>2mm) were consistently higher in middens than in bulk soil. Total C and N concentrations, C:N ratios, and microbial activity also were greatest in midden soil. Concentrations of ammonium-nitrogen and dissolved organic N were greater in middens than in bulk soil on most dates, suggesting accelerated decomposition and mineralization in middens. However, concentrations of nitrate were usually lower in middens, indicating reduced nitrification or increased leaching and denitrification losses from middens, relative to bulk soil. Fungal activity, as well as total microbial activity, was consistently greater in middens. The contribution of fungae to overall microbial activity differed significantly between middens and bulk soil only on one date when both soils were very dry; the contribution of fungae to microbial activity was lower in the middens on this date. We conclude that the midden-forming activity of L. terrestris can be a major determinant of spatial heterogeneity in some agricultural soils, and that this can potentially affect overall rates of soil processes such as organic matter decomposition, N mineralization, denitrification, and leaching. Received: 4 April 1997     

Biological and microbial activity in biological soil crusts from the Tabernas desert,a sub-arid zone in SE Spain

The ecology and functional role of biological soil crusts (BSCs) in arid and semi-arid zones have been extremely well studied. However, little is known about the biochemical properties related to the number and activity of the microbiota that form the crusts, even though information about these properties is very important for understanding many of the processes that affect the formations. In this study, several properties related to the activity and number of microorganisms (biomass-C, basal respiration, dehydrogenase activity and nitrogen mineralization potential) were determined at different depths (crusts, 0–0.5 cm; middle, 0.5–3 cm and deep, 3–5 cm layers) in two types of crusts (predominated by cyanobacteria and by lichens) in the Tabernas desert (Almeria, SE Spain). The absolute values of the above-mentioned properties and the values expressed relative to the total organic carbon (TOC) content were both much higher in the crust layers than in the surface horizons of soils under Mediterranean or Atlantic climates. A large part of the TOC in the BSCs was contained in the microbiota and another large part was readily metabolized during incubation of the crusts for 10 days at 25 °C. The net nitrogen mineralization rate was also high, and ammonification predominated in the crust layers, whereas nitrification predominated in the middle and deep layers. In all types of BSCs, the microbiota colonized the deep layers, although with greater intensity in the lichen-dominated BSCs than in the cyanobacterial BSCs. The results also indicate that hydrolytic enzymes are not stabilized on soil colloids and their activity depends only on the active microbiota.     

Plant endemism and natural protected areas in the peninsula of Baja California, Mexico

The Peninsula of Baja California, Mexico has long been recognized as a hotspot for plant richness and endemism. However, its extraordinary diversity is not adequately protected by the existing protected areas. We analyzed the distribution of the endemic vascular flora of the peninsula, and its presence or absence in protected areas. We also identified regions with greater numbers of endemic species not currently under protected status. The families Asteraceae, Cactaceae, and Fabaceae alone contain 40% of the endemic species. All the peninsular species within the Begoniaceae, Thymeliaceae, Araliaceae and Hippocastanaceae are endemic. Of the total number of endemic taxa in the region, 76.4% are present within protected areas. The endemic genera Adenothamnus, Carterothamnus, Faxonia, and Ornithostaphylos are entirely absent from protected areas. Of the 567 endemics found in protected areas 75 represent varieties or subspecies Of the 175 not found in protected areas 21 are varieties or subspecies. A gap analysis identified that the areas with the highest number of unprotected endemic species are in the Mediterranean-type ecosystems of the north-west part of the peninsula and in the deciduous dry tropical communities of the cape region at the southernmost tip of Baja California. Our findings suggest that it is necessary to create several protected areas along the peninsula for the successful conservation of rare and endemic taxa These new areas should encompass a latitudinal gradient of biogeographical units (including Mediterranean communities and montane habitats of the Sierras) along the peninsula.     

荒漠盐生植物根际土壤酶活性的变化

利用根袋法研究了荒漠盐土和灌耕灰漠土中6种不同荒漠盐生植物根际养分和酶活性特征.结果表明:两种土壤中,根际土全氮含量比非根际土高,但全磷却比非根际土低.根际土有效态养分的变化则与全态相反,6种植物的根际土有效氮含量均显著低于非根际土,除芦苇外,根际土有效磷含量均高于非根际土.6种植物中,钠猪毛菜根际土有效氮亏缺最高,有效磷富集也最少.分析测定了根际土和非根际土转化酶、蛋白酶、过氧化氢酶、脲酶、中性磷酸酶和碱性磷酸酶活性及其与土壤养分的关系.结果表明:过氧化氢酶、脲酶和蛋白酶在两种土壤的植物根际表现出相反的变化,荒漠盐土中,根际土3种酶的活性均高于非根际土;而灌耕灰漠土的根际土3种酶活性均低于非根际土.荒漠盐土碱性磷酸酶、过氧化氢酶和转化酶与几种主要养分含量有很强的相关性,较好地体现了荒漠盐土根际的养分状况,也说明盐生植物对荒漠盐土酶活性有较大的影响.     

Denitrification under different cultivated plants: effects of soil moisture tension,nitrate concentration,and photosynthetic activity

Summary Plant effects on the denitrification rate were investigated in pot experiments at different soil moisture tensions and nitrate concentrations. Nitrate concentrations and the soil moisture tension were regulated immediately before each measurement. The effects of the plants on denitrification rates were dependent on the soil moisture tension. At a low soil moisture tension (–7 cm H₂O), there was a 10-fold increase in the denitrification rate (planted versus unplanted soil). At a medium moisture tension (–30 cm H₂O) the plants had practically no effect, and at the highest tension (–60 cm H₂O) the effect was slightly negative. Large differences in denitrification rates under different plant species were observed. At a low soil moisture tension, the average denitrification rate (g N kg^–1 soil h^–1) was 39–42 under small grains (barley, wheat, and oats), 47–82 under the grasses (cocksfoot, meadow grass, meadow fescue, and timothy) and 18 under red clover. The differences between the monocots were attributable to differences in plant growth rates, rather than to any specific difference in stimulation or inhibition of denitrification, since the variations in photosynthetic activity fairly well predicted the differences in denitrification rates under different monocots. Clover, however, gave much lower denitrification rates than those predicted by the photosynthetic activity.     

Distribution of microbial communities in a forest soil profile investigated by microbial biomass, soil respiration and DGGE of total and extracellular DNA

We studied the distribution of the indigenous bacterial and fungal communities in a forest soil profile. The composition of bacterial and fungal communities was assessed by denaturing gradient gel electrophoresis (DGGE) of total and extracellular DNA extracted from all the soil horizons. Microbial biomass C and basal respiration were also measured to assess changes in both microbial biomass and activity throughout the soil profile. The 16S rDNA-DGGE revealed composite banding patterns reflecting the high bacterial diversity as expected for a forest soil, whereas 18S rDNA-DGGE analysis showed a certain stability and a lower diversity in the fungal communities. The banding patterns of the different horizons reflected changes in the microbial community structure with increasing depth. In particular, the DGGE analysis evidenced complex banding patterns for the upper A1 and A2 horizons, and a less diverse microflora in the deeper horizons. The low diversity and the presence of specific microbial communities in the B horizons, and in particular in the deeper ones, can be attributed to the selective environment represented by this portion of the soil profile. The eubacterial profiles obtained from the extracellular DNA revealed the presence of some bands not present in the total DNA patterns. This could be interpreted as the remainders of bacteria not any more present in the soil because of changes of edaphic conditions and consequent shifting in the microbial composition. These characteristic bands, present in all the horizons with the exception of the A1, should support the concept that the extracellular DNA is able to persist within the soil. Furthermore, the comparison between the total and extracellular 16S rDNA-DGGE profiles suggested a downwards movement of the extracellular DNA.     

Physical characterization,spectral response and remotely sensed mapping of Mediterranean soil surface crusts

Soil surface crusting and sealing are frequent but unfavorable processes in Mediterranean areas. Soil crust and seals form on bare soil subject to high-intensity rainfall, resulting in a hard, impenetrable layer that impedes infiltration and hampers the germination and establishment of plants. The adverse consequences of overland flow and reduced fertility can lead to erosion and ongoing degradation. Therefore, information on the distribution of surface crusts and their physical properties is essential to combat the undesired effects of crust formation in e.g. soil erosion and soil compaction. We studied the occurrence of crusts in a study area in Mediterranean southern France. Our objectives were to compare the physical and hydrological properties of the crusts and underlying soil, to identify the spectral characteristics (400 to 2500 nm) of the crusted and non-crusted soil surfaces using high-resolution field spectra, and to investigate the potential of mapping crust occurrence using airborne, hyperspectral HyMap images. The differences in some physical properties between crusted and non-crusted surfaces are significant while others are only marginal. Crusting markedly reduces the infiltration capacity and crust strength varies between the different soil types. Spectral differences are small, mainly in albedo values (overall reflectance) and in absorption band depth and shape. Albedo differences range from 8 to 40%. Differences in absorption band features in the spectra of crusts and non-crusted surfaces are small. Sixty percent of the crusted soil surfaces showed stronger absorption features in the clay mineral absorption bands at 2200 nm than non-crusted soils. Increased absorption is due to a relative enrichment in fines. Spectral feature fitting and linear spectral unmixing algorithms were applied to airborne HyMap images to evaluate the possibilities of mapping surface crusts. Crusts could be mapped in fallow, agricultural fields, but the spectral response of natural badlands was too fragmented for crust mapping.     

Estimates of sea turtle mortality from poaching and bycatch in Bahía Magdalena, Baja California Sur, Mexico

Bahia Magdalena on the Pacific coast of Baja California Sur, Mexico, is an important feeding and nursery ground for black turtles Chelonia mydas, loggerhead turtles Caretta caretta, olive ridley turtles Lepidochelys olivacea, and hawksbill turtles Eretmochelys imbricata. Despite international and national protection, sea turtles continue to be caught incidentally and hunted for consumption in large numbers. This study examines the mortality of sea turtles in Bahia Magdalena, focusing on (1) species distribution and number of carcasses found, (2) causes of death, (3) size frequency distribution and % juveniles in the catch, and (4) changes in average size over the past years. A total of 1945 turtle carcasses were found from April 2000 to July 2003 along beaches and in towns of the region with loggerhead (44.1%) and black turtles (36.9%) being the dominant species. Slaughter for human consumption was the primary cause of death of carcasses found in towns (95-100%), while carcasses on beaches mostly died of unknown causes (76-100%). Circumstantial evidence suggests however, that incidental bycatch was the main mortality cause on beaches. Black turtles suffered the highest consumption mortality overall (91%), followed by olive ridley (84%), hawksbill (83%) and loggerhead turtles (63%). Over 90% of all turtles found were juveniles or subadults. Carapace length of black turtles declined consistently over the sampling period, while that of loggerhead turtles increased. Our results strongly suggest that turtles are being taken at high and unsustainable rates; this may partially explain why the populations have not recovered despite widespread protection on nesting beaches.     

荒漠草原土壤酶与土壤养分的动态研究

研究了内蒙古荒漠草原不同利用强度单元内土壤养分以及5种酶活性,并对土壤酶活性与土壤养分含量之间的相关性进行了分析。结果表明,草原的利用强度直接影响着草地的土壤养分状况和酶活性,轻度利用有利于土壤中5种酶活性的增加,重度利用则导致土壤转化酶和蛋白酶活性显著降低。轻度利用增加了土壤中有机质、全氮和全磷的含量,重度利用则导致土壤有机质、全磷、全氮和全钾含量降低。脲酶和多酚氧化酶的活性在年季内变化幅度较大。相关性分析表明,蛋白酶与各养分之间的相关性最大。     

Nano-scale secondary ion mass spectrometry — A new analytical tool in biogeochemistry and soil ecology: A review article

Soils are structurally heterogeneous across a wide range of spatio-temporal scales. Consequently, external environmental conditions do not have a uniform effect throughout the soil, resulting in a large diversity of micro-habitats. It has been suggested that soil function can be studied without explicit consideration of such fine detail, but recent research has indicated that the micro-scale distribution of organisms may be of importance for a mechanistic understanding of many soil functions. Current techniques still lack the adequate sensitivity and resolution for data collection at the micro-scale, and the question ‘How important are various soil processes acting at different scales for ecological function?’ is therefore challenging to answer. The nano-scale secondary ion mass spectrometer (NanoSIMS) represents the latest generation of ion microprobes, which link high-resolution microscopy with isotopic analysis. The main advantage of NanoSIMS over other secondary ion mass spectrometers is its ability to operate at high mass resolution, whilst maintaining both excellent signal transmission and spatial resolution (down to 50 nm). NanoSIMS has been used previously in studies focussing on presolar materials from meteorites, in material science, biology, geology and mineralogy. Recently, the potential of NanoSIMS as a new tool in the study of biophysical interfaces in soils has been demonstrated. This paper describes the principles of NanoSIMS and discusses the potential of this tool to contribute to the field of biogeochemistry and soil ecology. Practical considerations (sample size and preparation, simultaneous collection of isotopes, mass resolution, isobaric interference and quantification of the isotopes of interest) are discussed. Adequate sample preparation, avoiding bias due to artefacts, and identification of regions-of-interest will be critical concerns if NanoSIMS is used as a new tool in biogeochemistry and soil ecology. Finally, we review the areas of research most likely to benefit from the high spatial and high mass resolution attainable with this new approach.     

Microbial characteristics of ectomycorrhizal mat communities in Oregon and California

Summary Specialized ectomycorrhizal fungi form dense mats in forest soils that have different enzyme levels, higher respiration rates, more biomass, different soil fauna, and different soil chemistry compared with adjacent soils not obviously colonized by these mats. In this study, mats formed by two genera of fungi collected in three locations were compared with a wide range of measurements. Per cent moisture, pH, chloroform fumigation-flush C, anaerobic N mineralization, exchangeable ammonium, and respiration, N₂ fixation, and denitrification rates were compared between soils or litter colonized by ectomycorrhizal mat-forming fungi and adjacent non-mat material. Significant differences were observed between the two genera of mat-forming fungi and also between mats formed primarily in mineral soil and those formed in litter. These differences suggest that different mat-forming fungi perform different functions in forest soils and that these fungi function differently in mineral soil compared with litter.Published as Technical Paper 9496, Oregon Agricultural Experiment Station     

Soil surface disturbances in cold deserts: effects on nitrogenase activity in cyanobacterial-lichen soil crusts

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.     

Conservation of soil moisture by different stone covers on alpine talus slopes (Lassen, California)

This study reports on the influence of stone covers with different clast sizes on the soil moisture of alpine talus slopes in Lassen (California). Fifteen four-plot sets were sampled in the dry season (July 1990) in sandy areas and in talus covered with pebbles, cobbles, or blocks between 2740 and 2775 m. Three depths (0–5, 5–10, 10–15 cm) were sampled. Field moisture content increased gradually with depth in all soil profiles, and also in plots covered by increasingly larger rocks. Surface soils in sand areas were very dry, but under rocks had water contents 6 to 14 times greater. Differences among plots decreased with depth, but subsoil samples in sand were still drier than those beneath any stone cover at similar depths. Blocks were most effective in conserving moisture; water content below them was higher than even in deep (10–15 cm) sand soils. Soil temperatures were recorded in sand and under blocks for an 11-day period. Minima were not significantly different, but average maxima were 5.6°C lower under blocks than in sand, which reached highs 4.4°C lower than the air. Differences in soil moisture among talus types are ascribed to lower evaporation losses under stones, due to both disruption of capillarity by the coarse particles, which prevented water flow to the talus surface, and to their efficient reduction of maximum temperatures. An irrigation experiment was conducted at 2110 m on a steep talus on the Chaos Crags from July 18 to Aug. 2, 1993. Four 100×75 cm plots with the same surface types than at Lassen received 22.5 mm water; moisture content was then periodically sampled. Watering produced similar water distributions among soil depths and talus types to those in Lassen. Evaporation occurred quickly in bare soils due to high air and soil temperatures. The sand surface was already dry 2 days after watering, but stone-covered plots remained moist until day 15, when soils under blocks still retained 77–97% of the water content (percent by weight) at the start of the test.     

Microbiotic soil crusts in the Sahel of Western Niger and their influence on soil porosity and water dynamics

Microbiotic soil crusts are common features of the surface of fallow land in Western Niger. We investigated the interaction between these microbial covers and the porosity and water dynamics of soils at the surface of a Sahelian landscape. The soil pore system was examined by microscopic observations and mercury porosimetry. The soil water retention capacity was measured using a Richard pressure membrane apparatus. Runoff measurements were performed in situ at a 1 m² scale under natural rainfall.     

Nodulation of African yam bean (Sphenostylis stenocarpa) by Bradyrhizobium sp. isolated from Erythrina brucei

African yam bean (Sphenostylis stenocarpa), which is widely cultivated in Africa because of its growth capability on marginal soils, was nodulated by an endosymbiont (characterized and designed Bradyrhizobium sp. AUEB20) isolated from the Ethiopian tree Erythrina brucei with the formation of a small number of large, indeterminate N₂-fixing nodules. In contrast, 24 other isolates from Ethiopian woody legumes were ineffective. Strain AUEB20 promiscuously nodulated a number of tropical legumes, but none out of five European crop plants tested. Received: 17 September 1996     

Effects of biological soil crusts on soil enzyme activities in revegetated areas of the Tengger Desert,China

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.     

Pu同位素在土壤侵蚀示踪中的应用

137Cs示踪技术目前在土壤侵蚀研究中应用最为广泛,但是随着环境中137Cs的衰变,寻找可以替代的放射性核素具有十分重要的意义。人造放射性核素Pu同位素与137Cs来源相同,但半衰期更长,且更容易被土壤中的细颗粒物质吸附。特别是随着测量技术的发展,电感耦合等离子体质谱技术(ICP-MS)以及加速器质谱技术(AMS)等的应用,使得Pu同位素的测量较137Cs更高效、灵敏。因而Pu同位素成为可以替代137Cs进行土壤侵蚀示踪的理想元素。本文从Pu的来源及分布、Pu在土壤中的吸附和固定、Pu同位素的测量方法三个方面分析Pu同位素示踪土壤侵蚀的基础,并对Pu同位素示踪土壤侵蚀的基本原理和应用现状加以简述,探讨了今后Pu同位素在土壤侵蚀示踪应用中的主要研究方向。