Arid Land Soils Research Articles

Feasibility of Vis-NIR spectroscopy approach to predict soil biological attributes in arid land soils.

Visible and near-infrared (Vis-NIR) reflectance spectroscopy has recently emerged as an efficient and cost-effective tool for monitoring soil parameters and provides an extensive array of measurements swiftly. This study sought to predict fundamental biological attributes of calcareous soils using spectral reflectance data in the Vis-NIR range through the application of partial least square regression (PLSR) and stepwise multiple linear regression (SMLR) techniques. The objective was to derive spectrotransfer functions (STFs) to predict selected soil biological attributes. A total of 97 composite samples were collected from three distinct agricultural land uses, i.e., sugarcane, wheat, and date palm, in the Khuzestan Province, Iran. The samples were analyzed using both standard laboratory analysis and proximal sensing approach within the Vis-NIR range (400-2500 nm). Biological status was evaluated by determining soil enzyme activities linked to nutrient cycling including acid phosphatase (ACP), alkaline phosphatase (ALP), dehydrogenase (DEH), soil microbial respiration (SMR), microbial biomass phosphorus (Pmic), and microbial biomass carbon (Cmic). The results indicated that the developed PLSR models exhibited superior predictive performance in most biological parameters compared to the STFs, although the differences were not significant. Specifically, the STFs acceptably accurately predicted ACP, ALP, DEH, SMR, Pmic, and Cmic with R2val (val = validation dataset) values of 0.68, 0.67, 0.65, 0.65, 0.76, and 0.72, respectively. These findings confirm the potential of Vis-NIR spectroscopy and the effectiveness of the associated STFs as a rapid and reliable technique for assessing biological soil quality. Overall, in the context of predicting soil properties using spectroscopy-based approaches, emphasis must be placed on developing straightforward, easily deployable, and pragmatic STFs.

Effects of Irrigation Interval and Planting Spacing on the Establishment and Growth of Faidherbia albida (Del.) A. Chev. Transplants in Arid Land Soils

The study aimed to assess the establishment of Faidherbiaalbida transplants under the effect of irrigation intervals and plantingspacing in the field conditions. It consisted of three irrigation intervals of5, 10 and 15 days and three planting spacings of 1x1 m, 1x2 m, and 2x3m; and it was conducted in the premises of the Forest Research Center,Khartoum, during May 2008 to June 2009. The results showed that thetemporal growth rate of F. albida shoot heights was greater in winter(November-February), but it was seriously slowed during the summerperiod (March-June). The shoot height, diameter and biomass growth ofF. albida increased with decreasing irrigation intervals; the growth ofthese parameters was highest in 5 days interval and lowest in 15 daysinterval. Planting spacings had no direct definite effect on F. albidaseedlings’ growth parameters. Even though, in the longer irrigationintervals, transplants’ growth tented to be greater in the wider spacing.Root biomass development seemed to be higher in the longer irrigationinterval regimes. There were no significant differences in the foliarnutrient content of the transplants between the different irrigationintervals. The values of mineral elements measured in this study areindicative of moderate nutrient supply for the F. albida transplants

Rapid remodeling of the soil lipidome in response to a drying-rewetting event

BackgroundMicrobiomes contribute to multiple ecosystem services by transforming organic matter in the soil. Extreme shifts in the environment, such as drying-rewetting cycles during drought, can impact the microbial metabolism of organic matter by altering microbial physiology and function. These physiological responses are mediated in part by lipids that are responsible for regulating interactions between cells and the environment. Despite this critical role in regulating the microbial response to stress, little is known about microbial lipids and metabolites in the soil or how they influence phenotypes that are expressed under drying-rewetting cycles. To address this knowledge gap, we conducted a soil incubation experiment to simulate soil drying during a summer drought of an arid grassland, then measured the response of the soil lipidome and metabolome during the first 3 h after wet-up.ResultsReduced nutrient access during soil drying incurred a replacement of membrane phospholipids, resulting in a diminished abundance of multiple phosphorus-rich membrane lipids. The hot and dry conditions increased the prevalence of sphingolipids and lipids containing long-chain polyunsaturated fatty acids, both of which are associated with heat and osmotic stress-mitigating properties in fungi. This novel finding suggests that lipids commonly present in eukaryotes such as fungi may play a significant role in supporting community resilience displayed by arid land soil microbiomes during drought. As early as 10 min after rewetting dry soil, distinct changes were observed in several lipids that had bacterial signatures including a rapid increase in the abundance of glycerophospholipids with saturated and short fatty acid chains, prototypical of bacterial membrane lipids. Polar metabolites including disaccharides, nucleic acids, organic acids, inositols, and amino acids also increased in abundance upon rewetting. This rapid metabolic reactivation and growth after rewetting coincided with an increase in the relative abundance of firmicutes, suggesting that members of this phylum were positively impacted by rewetting.ConclusionsOur study revealed specific changes in lipids and metabolites that are indicative of stress adaptation, substrate use, and cellular recovery during soil drying and subsequent rewetting. The drought-induced nutrient limitation was reflected in the lipidome and polar metabolome, both of which rapidly shifted (within hours) upon rewet. Reduced nutrient access in dry soil caused the replacement of glycerophospholipids with phosphorus-free lipids and impeded resource-expensive osmolyte accumulation. Elevated levels of ceramides and lipids with long-chain polyunsaturated fatty acids in dry soil suggest that lipids likely play an important role in the drought tolerance of microbial taxa capable of synthesizing these lipids. An increasing abundance of bacterial glycerophospholipids and triacylglycerols with fatty acids typical of bacteria and polar metabolites suggest a metabolic recovery in representative bacteria once the environmental conditions are conducive for growth. These results underscore the importance of the soil lipidome as a robust indicator of microbial community responses, especially at the short time scales of cell-environment reactions.A8GGwc64vbJf6mXPFnxxi9Video

Bentonite clay combined with organic amendments to enhance soil fertility in oasis agrosystem

Soils in arid and semi-arid lands are vulnerable to climate change, erosion, and mismanagement practices that contribute to organic matter depletion and nutrients imbalances. Oasis agrosystems are considered one of the major farming systems in some parts of these lands in the Middle East and North Africa region. However, oases soils are inherently low in organic carbon due to their sandy texture which retains little water and binds low organic matter contents, and the accelerated decomposition rates of organic matter under high temperature, which makes its accumulation difficult. Traditional farming practices in oasis agrosystems have always integrated organic matter derived from livestock to enhance organic carbon (OC) and total nitrogen (TN) stocks in the soil. This study is aimed to examine the potential effects of a new mixture of organic amendments and bentonite clay on organic carbon and total nitrogen stock accumulation in the soil. Five amendments were applied including sand and compost (SC), sand and manure (SM), sand, bentonite, and compost (SBC), sand, bentonite, and manure (SBM), and sand mixed with bentonite (SB). These treatments were compared to untreated soil (U). The results showed that OC and TN stocks increased significantly (p<0.05) in all three depths of the five treatments compared to the untreated soil. Higher organic carbon stocks (2862±3.4 g m−2) were detected in SBM treatment. The combined organic and mineral amendment retarded OC and TN decomposition. After two years of the amendments’ application, 30% of OC remained in the soil for SBC treatment. In conclusion, the mixed mineral and organic amendment is a better choice to preserve OC and, thus, maintain oasis soil fertility.

Monitoring the Efficiency of Rhazya stricta L. Plants in Phytoremediation of Heavy Metal-Contaminated Soil.

Heavy metal-contaminated soil constitutes many environmental concerns. The toxic nature of heavy metals poses serious threats to human health and the ecosystem. Decontamination of the polluted soil by phytoremediation is of fundamental importance. Vegetation is an appealing and cost-effective green technology for the large-scale phytoremediation of polluted soils. In this paper, a greenhouse experiment was carried out to test the potential of Rhazya stricta as a heavy metal phytoremediator in polluted soil. Plants were grown for three months in pots filled with soils treated with the heavy metals Cd, Pb, Cu, and Zn at rates of 10, 50, and 100 mg/kg. The bioaccumulation factor (BCF) and translocation factor (TF) were calculated to detect the ability of R. stricta to accumulate and transfer heavy metals from soil to plant organs. The results showed that under increasing levels of soil pollution, the bioconcentration of Cd and Zn heavy metals showed the highest values in plant roots followed by leaves, whereas in the case of Pb and Cu, roots showed the highest values followed by stems. Heavy metals accumulation was higher in roots than in stems and leaves. The BCF of Zn reached the highest values in roots and stems for 10 mg/kg soil treatment, followed by the BCFs of Cd, Cu, and Pb. The TF for the different heavy metal pollutants’ concentrations was less than unity, suggesting that the plants remediate pollutants by phytostabilization. The TF values ranged from higher to lower were in the order Zn > Cu > Cd > Pb. The rapid growth of R. stricta and its tolerance of heavy metals, as well as its ability to absorb and accumulate metals within the plant, recommends its use in the phytoremediation of slightly polluted soils in arid lands by limiting the heavy metals transport.

Anammox bacterial abundance and biodiversity in greenhouse vegetable soil are influenced by high nitrate content

The anaerobic ammonium oxidizing (anammox) process has been found to play an important role in terrestrial ecosystems in recent years. However, the diversity and abundance of anammox bacteria in nitrogen (N)-rich agricultural soils under high fertilizer greenhouse conditions are still unclear. Two greenhouse fields with different N fertilizer input levels were chosen, and their soil profiles were studied with molecular technologies, including quantitative polymerase chain reaction assay, a clone library, and phylogenetic analysis based on hzsB (encoding anammox hydrazine synthase β-subunit) gene. Molecular analyses suggested that anammox bacteria were at their highest density at 10–20 cm soil depth, and that the anammox bacterial abundance was significantly lower at high N than at low N. Candidatus Brocadia was the sole anammox bacterial genus throughout the soil depth profiles. The highest diversity of anammox bacteria was found at 30–40 cm soil depth, and different phylotypic clusters of Candidatus Brocadia were associated with specific soil environmental factors, such as nitrates, soil depth, and total N. Correlation analyses and redundancy analyses confirmed that high nitrate content associated with high N fertilizer input had a significant negative influence on the abundance and biodiversity of anammox bacteria. These results imply that excessive use of N fertilizer would affect arid land soil N loss to the atmosphere by the anammox pathway.

Optimizing the Production of Nursery-Based Biological Soil Crusts for Restoration of Arid Land Soils.

Biological soil crusts (biocrusts) are topsoil communities formed by cyanobacteria or other microbial primary producers and are typical of arid and semiarid environments. Biocrusts promote a range of ecosystem services, such as erosion resistance and soil fertility, but their degradation by often anthropogenic disturbance brings about the loss of these services. This has prompted interest in developing restoration techniques. One approach is to source biocrust remnants from the area of interest for scale-up cultivation in a microbial "nursery" that produces large quantities of high-quality inoculum for field deployment. However, growth dynamics and the ability to reuse the produced inoculum for continued production have not been assessed. To optimize production, we followed nursery growth dynamics of biocrusts from cold (Great Basin) and hot (Chihuahuan) deserts. Peak phototrophic biomass was attained between 3 and 7 weeks in cold desert biocrusts and at 12 weeks in those from hot deserts. We also reused the resultant biocrust inoculum to seed successive incubations, tracking both phototroph biomass and cyanobacterial community structure using 16S rRNA gene amplicon sequencing. Hot desert biocrusts showed little to no viability upon reinoculation, while cold desert biocrusts continued to grow, but at the expense of progressive shifts in species composition. This leads us to discourage the reuse of nursery-grown inoculum. Surprisingly, growth was highly variable among replicates, and overall yields were low, a fact that we attribute to the demonstrable presence of virulent and stochastically distributed but hitherto unknown cyanobacterial pathogens. We provide recommendations to avoid pathogen incidence in the process.IMPORTANCE Biocrust communities provide important ecosystem services for arid land soils, such as soil surface stabilization promoting erosion resistance and contributing to overall soil fertility. Anthropogenic degradation to biocrust communities (through livestock grazing, agriculture, urban sprawl, and trampling) is common and significant, resulting in a loss of those ecosystem services. Losses impact both the health of the native ecosystem and the public health of local populations due to enhanced dust emissions. Because of this, approaches for biocrust restoration are being developed worldwide. Here, we present optimization of a nursery-based approach to scaling up the production of biocrust inoculum for field restoration with respect to temporal dynamics and reuse of biological materials. Unexpectedly, we also report on complex population dynamics, significant spatial variability, and lower than expected yields that we ascribe to the demonstrable presence of cyanobacterial pathogens, the spread of which may be enhanced by some of the nursery production standard practices.

Interactions between humic substances and organic amendments affecting soil biological properties and growth of Zea mays L. in the arid land region

Application of organic amendments to the arid land soils is a sustainable tool to improve soil fertility. A greenhouse experiment was conducted to find the effect of humic acid (HA), alfalfa residues (AR) (Medicago sativa L.), and sheep manure (SM) on soil respiration, soil organic carbon content, soil structure, total bacteria, total fungi, and growth of corn plant Zea mays L. Results showed that the highest aggregate stability was 44.2% for the HA + SM treatment whereas it was 9% for the HA treatment. The higher stability was associated with higher organic carbon 4.60%, and higher bacterial and fungal densities of 190 × 106 g−1 dry soil and 101 × 106 g−1, respectively. The HA + AR treatment did not increase aggregate stability significantly (27.7%), nor did the AR treatment (25.9%). Soil respiration over 70 days was significantly (p < 0.05) higher in the SM (42.9 CO2–C mg g−1) compared to the AR treatment (33.3 CO2–C mg g−1). In contrast, the HA + SM treatment had lower soil respiration (27.4 CO2–C mg g−1) compared to the SM treatment (42.9 CO2–C mg g−1). The HA + AR treatment recorded higher plant weight (20.6 g) compared to HA (10.2 g) and control treatments (8.11 g). This study proved that HA did not enhance soil structure or the microbial community, whereas the combination of HA with SM or AR is more effective at promoting the soil microbial community, soil aggregation, organic carbon content and plant growth in the saline, arid land.

Assessment of abundance and diversity of exoelectrogenic bacteria in soil under different land use types

Soil exoelectrogenic bacteria have been found to perform various functions. However, little is known about whether exoelectrogenic bacteria are widely distributed in soil and which physico-chemical properties of soil significantly affect their distribution? To address the research questions, 37 soil samples covering six land use types, including arid farmland soils, woodland soils, grassland soils, paddy soils, lakeshore soils, and coastal soils were collected. DNA was extracted from all the samples for quantitative PCR and high throughput sequencing of the 16S rRNA gene. The sequencing result showed a total of 16 exoelectrogenic bacteria-associated genera from different soils. The total abundance of these genera varied from 1.14 × 108 copies g−1 in a farmland soil to 7.89 × 109 copies g−1 in a coastal soil, accounting for 0.26% to 7.70% of the total bacteria. Among the 16 genera, Bacillus was dominant in the arid land soils, including the farmland, woodland, and grassland soils. The coastal soils were dominated by Desulfobulbus whereas the paddy and lakeshore soils were characterized by abundant Geobacter. Principal component analysis showed a distinct separation of the exoelectrogenic bacterial community between the arid land (farmland, woodland, and grassland soils), freshwater wetland (paddy and lakeshore soils), and coastal soils. Redundancy analysis revealed that the water content, electrical conductivity and concentrations of total sulphur and amorphous Fe in the soil were significant factors driving the community structure and abundance of exoelectrogenic bacteria-associated genera. Our results should help in better understanding of the exoelectrogenic bacteria-mediated functions in soil, which might contribute to the biogeochemical cycling of a large number of organic and inorganic materials.

Bacteria increase arid-land soil surface temperature through the production of sunscreens.

Soil surface temperature, an important driver of terrestrial biogeochemical processes, depends strongly on soil albedo, which can be significantly modified by factors such as plant cover. In sparsely vegetated lands, the soil surface can be colonized by photosynthetic microbes that build biocrust communities. Here we use concurrent physical, biochemical and microbiological analyses to show that mature biocrusts can increase surface soil temperature by as much as 10 °C through the accumulation of large quantities of a secondary metabolite, the microbial sunscreen scytonemin, produced by a group of late-successional cyanobacteria. Scytonemin accumulation decreases soil albedo significantly. Such localized warming has apparent and immediate consequences for the soil microbiome, inducing the replacement of thermosensitive bacterial species with more thermotolerant forms. These results reveal that not only vegetation but also microorganisms are a factor in modifying terrestrial albedo, potentially impacting biosphere feedbacks on past and future climate, and call for a direct assessment of such effects at larger scales.

Sediment concentration and hydraulic characteristics of rain-induced overland flows in arid land soils

Purpose Rain-induced overland flow involves the detachment of soil particles by raindrop impact and the transportation by the resultant overland flow. The purpose of this study was to investigate the relationship between sediment concentration and different hydraulic parameters including flow depth, flow velocity, shear stress, stream power, and unit stream power. The effects of soil particle size distribution, rain intensity, and slope steepness on measured sediment concentration in rain-induced sheet flow were also examined.

Phytoremediation of soils polluted with crude petroleum oil using Bassia scoparia and its associated rhizosphere microorganisms

The ability of Bassia scoparia (L.) A. J. Scott to remediate petroleum-contaminated arid land sandy soil was studied with natural and sterilized soils, and with supplemental nutrients and water. The species showed good tolerance of petroleum hydrocarbons (PHs) in soils reaching 2–3% (oil:soil by mass) pollution levels. After five months of phytoremediation, the average degradation rate of petroleum hydrocarbons ranged between 31.2 ± 1.15–57.7 ± 1.29% for natural soil and 28.7 ± 1.04–51.1 ± 1.53% for pre-sterilized soil. The highest breakdown of PHs for both saturated and poly-aromatic fractions was achieved when plants were present. Changes in saturated and aromatic fractions were monitored and measured using gas chromatography and high performance liquid chromatography. Moderate concentrations of PHs activated specialized oil-degrading microorganisms which in turn promoted the efficiency of phytoremediation. Polluted soils planted with B. scoparia also showed a significant reduction in sulfur levels. The potential demonstrated for remediation of petroleum hydrocarbons and sulfur by B. scoparia suggests it may be a useful tool for remediation of arid land soils contaminated with crude oil.

Ammonia-oxidizing archaea respond positively to inorganic nitrogen addition in desert soils.

In soils, nitrogen (N) addition typically enhances ammonia oxidation (AO) rates and increases the population density of ammonia-oxidizing bacteria (AOB), but not that of ammonia-oxidizing archaea (AOA). We asked if long-term inorganic N addition also has similar consequences in arid land soils, an understudied yet spatially ubiquitous ecosystem type. Using Sonoran Desert top soils from between and under shrubs within a long-term N-enrichment experiment, we determined community concentration-response kinetics of AO and measured the total and relative abundance of AOA and AOB based on amoA gene abundance. As expected, N addition increased maximum AO rates and the abundance of bacterial amoA genes compared to the controls. Surprisingly, N addition also increased the abundance of archaeal amoA genes. We did not detect any major effects of N addition on ammonia-oxidizing community composition. The ammonia-oxidizing communities in these desert soils were dominated by AOA as expected (78% of amoA gene copies were related to Nitrososphaera), but contained unusually high contributions of Nitrosomonas (18%) and unusually low numbers of Nitrosospira (2%). This study highlights unique traits of ammonia oxidizers in arid lands, which should be considered globally in predictions of AO responses to changes in N availability.

The implications of environmental trading mechanisms on a future Zero Net Land Degradation protocol

Despite many important success stories around the planet, there is general disappointment at the overall impact of the United Nations Convention to Combat Desertification (hereinafter: UNCCD) during its first 20 years, with soil degradation still a challenge for land managers throughout much of the world's drylands. Calls for a new protocol under the UNCCD that will ensure “Zero Net Land Degradation” (ZNLD) have gained momentum since the tacit endorsement of the concept at the 2012 Rio + 20 summit. There is great conceptual appeal to a framework that implicitly allows for development by balancing associated soil fertility loss with commensurate gains resulting from restoration activities. Trading programs which seek to reach “zero net” degradation of other natural resources have been in place for many years now internationally and offer an important basis for assessing the practical and theoretical problems that are likely to arise under a ZNLD framework. This article summarizes the relevant experiences garnered in “offsetting” regulatory schemes in the areas of wetland preservation, biodiversity, forestry, greenhouse gas emissions mitigation, real estate zoning, and conventional air pollution control. While many of these initiatives take place in environments with completely different climatic conditions, they offer important lessons for ZNLD advocates. Pitfalls in offset programs are identified in the areas of: reliability of trades; clear quantifiable units of measure; equivalence given land heterogeneity; and delayed benefits. The article contains a series of recommendations for land degradation offsets based on this diverse international experience. Proven implementation strategies should inform any future ZNLD policies as part of national and regional regulatory programs to combat desertification and arid land soil degradation.

Evaluation of In Vitro Ovicidal Activity of Ethanolic Extracts of Prosopis juliflora (Sw.) DC (Fabaceae)

Gastrointestinal nematode infections in ruminants have direct effects such as mortality, weaknesses, feeding efficiency and decreased productivity. Animal deaths due to nematode infections are common in tropical regions where control programs based solely on the use of synthetic anthelmintics are no longer sustainable due to increased prevalence of gastrointestinal nematode resistance, slow development of new anthelmintics, high costs to poor farmers and concerns regarding residue in food and the environment. Alternative methods of control are thus required. Prosopis juliflora is a fast-growing, drought-resistant tree adapted to poor and saline soils in arid and semi-arid lands of Kenya, inhabited by nomadic pastoralists. Analysis of the EHA data using t- test revealed that there was no statistically significant difference in the activities of both LEE and REE (p>0.05). However, in comparison to ALB, the difference in activity was significantly different (p<0.05). The observed in vitro anthelmintic activity was attributed to saponins and condensed tannins and to alkaloids present in the plant. Phytochemical analysis confirmed presence of tannins, saponins and alkaloids, among other phytoconstituents. These phytochemicals are known to exhibit anthelmintic activity, therefore making the plant a potential candidate for drug development against gastrointestinal nematodes.

Nocturnal soil CO2 uptake and its relationship to subsurface soil and ecosystem carbon fluxes in a Chihuahuan Desert shrubland

AbstractDespite their prevalence, little attention has been given to quantifying arid land soil and ecosystem carbon fluxes over prolonged, annually occurring dry periods. We measured soil [CO2] profiles and fluxes (Fs) along with volumetric soil moisture and temperature in bare interplant canopy soils and in soils under plant canopies over a three‐month hot and dry period in a Chihuahuan Desert shrubland. Nocturnal Fs was frequently negative (from the atmosphere into the soil), a form of inorganic carbon exchange infrequently observed in other deserts. Negative Fs depended on air‐soil temperature gradients and were more frequent and stronger in intercanopy soils. Daily integrated ecosystem‐level Fs was always positive despite lower daily Fs in intercanopy soils due to nocturnal uptake and more limited positive response to isolated rains. Subsurface [CO2] profiles associated with negative Fs indicated that sustained carbonate dissolution lowered shallow‐soil [CO2] below atmospheric levels. In the morning, positive surface Fs started earlier and increased faster than shallow‐soil Fs, which was bidirectional, with upward flux toward the surface and downward flux into deeper soils. These dynamics are consistent with carbonate precipitation in conjunction with convection‐assisted CO2 outgassing from warming air and soil temperatures and produced a pronounced diurnal Fs temperature hysteresis. We concluded that abiotic nocturnal soil CO2 uptake, through a small carbon sink, modulates dry season ecosystem‐level carbon dynamics. Moreover, these abiotic carbon dynamics may be affected by future higher atmospheric carbon dioxide levels and predictions of more prolonged and regular hot and dry periods.

Fungi mediate nitrous oxide production but not ammonia oxidation in aridland soils of the southwestern US

Nitrification and denitrification are key processes that control nitrogen (N) availability and loss in terrestrial systems. Nitrification in soils is thought to be performed primarily by chemoautotrophic prokaryotes such as bacteria and archaea, and denitrification by bacterial heterotrophs. However, recent work in drylands suggests that fungi may play a larger role in N transformations than previously recognized. Arid and semi-arid ecosystems experience extreme temperatures and low moisture conditions, both of which favor growth and survival of some fungi, but the extent of fungal nitrification and denitrification in these soils has not been explored. We investigated the role of fungi in nitrate (NO3−) and nitrous oxide (N2O) production in soils from regions across the southwestern US. Soils were collected from urban and Sonoran Desert sites within the Phoenix metropolitan area in Arizona, and from grasslands in Arizona and New Mexico. Rates of potential nitrification were measured in soils subjected to biocide treatments (fungal and bacterial inhibitors) and acetylene, an inhibitor of autotrophic ammonia oxidation. Nitrous oxide production was measured from soils incubated at two moisture levels in the presence of the biocide treatments. Rates of potential nitrification decreased significantly in all soils with additions of acetylene, indicating that autotrophic microorganisms may dominate ammonia oxidation and NO3− production rather than heterotrophs (e.g., fungi). Similarly, fungi played a minor role in N2O production in urban turfgrass soils that were highly managed with irrigation and fertilizers. In contrast, fungi were major sources of N2O production in desert and semi-arid grassland soils across a range of soil water content. We conclude that fungi are likely responsible for denitrification in aridland soils, and that land-use changes associated with urbanization alter the biotic pathways responsible for N cycling.

Fraction of Cd in oasis soil and its bioavailability to commonly grown crops in Northwest China

Heavy metals in the soil–plant system resulting from mining and wastewater irrigation have greatly threatened human health and sustainable development in Northwest China. This research used pot experiments to study the bioavailability of Cd in irrigated desert soil from the oasis regions and conducted a human health risk assessment of the Cd content in vegetables. The results show that the content of Cd associated with exchangeable and carbonate metal fractionations is not uniform in arid oasis soils cultivated with the commonly grown vegetables. These common growth vegetables are: Cole (Brassica campestris L.), Celery (Apium Graveolens L.) and carrots (Daucus carota L.). The results show that the content of Cd in the edible part of cole was significantly higher than celery and carrots in almost all of the treatments. However, cole can grow normally and keep increasing its biomass at a sustainable rate under the highest concentration of Cd added in the experiment. Cole is not a suitable vegetable to be planted for consumption in arid soil contaminated with Cd, celery planted under lower concentration of Cd will not threaten human health, and carrots are suitable to be planted in arid soil contaminated with Cd even in the highest concentration used in the experiment. According to this conclusion, stricter soil management systems should be implemented to protect arid land soil resources and to protect human health from the toxicity impacts.

Structure of soil bacterial communities in relation to environmental variables in a semi-arid region of Mongolia

Patterns in soil bacterial communities, and the factors that determine them, have been little explored in arid and semi-arid environments. It is unclear to what extent the diversity and community composition of arid-land soil bacterial communities follow vegetation habitats, or conversely other relatively independent soil variables. It is also unclear whether the factors (e.g. pH) that contribute to variation in bacterial communities in some moister environments also operate on a local scale in semi-arid environments. To identify the main factors in shaping bacterial community structure in semi-arid environments, we sampled a mosaic of habitats under different vegetation, landscape and edaphic conditions in central Mongolia, including steppe, forest-steppe, and abandoned wheat field. Soil DNA was extracted and pyrosequenced for 16S rRNA gene identification. NMDS results showed that bacterial community structures are slightly different from one habitat to another. However, the similarity between communities both within and between habitats is determined more strongly by soil texture than by vegetation type and drainage conditions. Moreover, the relative abundances of certain phyla are correlated with specific soil properties such as salinity and soil texture, in ways that have not previously been found in semi-arid environments. Actinobacteria, for example, show a negative correlation with salinity and Bacteroidetes display a positive relationship with percentage silt and clay. It also appears that the most important environmental variables (soil texture and salinity) affecting the bacterial community within this semi-arid environment are different from those found in moister environments, with no detectable effect of pH.

Genome of the Cyanobacterium Microcoleus vaginatusFGP-2, a Photosynthetic Ecosystem Engineer of Arid Land Soil Biocrusts Worldwide

The filamentous cyanobacterium Microcoleus vaginatusis found in arid land soils worldwide. The genome of M. vaginatus strain FGP-2 allows exploration of genes involved in photosynthesis, desiccation tolerance, alkane production, and other features contributing to this organism's ability to function as a major component of biological soil crusts in arid lands.