Dryland Soils Research Articles

Illegal Dumping of Oil and Gas Wastewaters Alters Semi-Arid Soil Microbial Communities

The Permian Basin, underlying New Mexico and Texas, is one of the most productive oil and gas (OG) provinces in the United States. Oil and gas production yields large volumes of wastewater with complex chemistries. The environmental health risks posed by these OG wastewaters are not well understood, particularly in the case of accidental or intentional releases. Starting in November 2017, 39 illegal dumps of OG wastewater were identified in southeastern New Mexico that released approximately 6.4x105 liters of fluid onto desert soils. To evaluate the impacts of these releases on soils, we analyzed changes in soil geochemistry and microbial community composition by comparing soils from within OG wastewater dump-affected zones to corresponding unaffected zones with no known releases. We observed significant (p<0.01) changes in soil geochemistry for all dump-affected samples compared to controls, reflecting the residual salts and hydrocarbons left behind by the OG-wastewater release (e.g., enriched in sodium (Na), chloride (Cl), and bromide (Br)). Illumina 16S iTag sequencing revealed significant (p<0.01) differences in microbial community structure between dump and control zones. Furthermore, soils from dump areas had significantly (p<0.01) lower alpha diversity and exhibited differences in phylogenetic composition. Dump-affected soil samples showed an increase in halophilic and halotolerant taxa, such as members of the Marinobacteraceae, Halomonadaceae, and Halobacteroidaceae, suggesting that the high salinity of the dumped OG wastewater exerted a selective pressure on microbial communities. Taxa related to known hydrocarbon-degrading organisms, e.g., Marinobacter, Salegentibacter, Chromohalobacter, and Alcanivorax, were also detected in the dump-affected soil-sample communities. The microbial communities in control soils were dominated by taxa ubiquitous in, and well adapted to, arid and nutrient-deprived soil environments including photosynthetic Cyanobacteria, hydrogen-oxidizing Actinobacteria and Acidobacteria, and nitrogen-fixing Alphaproteobacteria. This study demonstrated that OG-wastewater dumps can lead to shifts in microbial community composition and function towards salt- and hydrocarbon-tolerant taxa that are not typically found in desert soils, thus altering the impacted dryland soil ecosystem. Loss of key microbial taxa, such as those that increase arid soil fertility, or promote plant health, could result in cascading affects to myriad ecosystem services such as loss of flora. Further studies are needed to explore the potential for using halophilic and hydrocarbon-degrading taxa to bioremediate OG-wastewater affected lands.

Cultivating Resilience in Dryland Soils: An Assisted Migration Approach to Biological Soil Crust Restoration.

Land use practices and climate change have driven substantial soil degradation across global drylands, impacting ecosystem functions and human livelihoods. Biological soil crusts, a common feature of dryland ecosystems, are under extensive exploration for their potential to restore the stability and fertility of degraded soils through the development of inoculants. However, stressful abiotic conditions often result in the failure of inoculation-based restoration in the field and may hinder the long-term success of biocrust restoration efforts. Taking an assisted migration approach, we cultivated biocrust inocula sourced from multiple hot-adapted sites (Mojave and Sonoran Deserts) in an outdoor facility at a cool desert site (Colorado Plateau). In addition to cultivating inoculum from each site, we created an inoculum mixture of biocrust from the Mojave Desert, Sonoran Desert, and Colorado Plateau. We then applied two habitat amelioration treatments to the cultivation site (growth substrate and shading) to enhance soil stability and water availability and reduce UV stress. Using marker gene sequencing, we found that the cultivated mixed inoculum comprised both local- and hot-adapted cyanobacteria at the end of cultivation but had similar cyanobacterial richness as each unmixed inoculum. All cultivated inocula had more cyanobacterial 16S rRNA gene copies and higher cyanobacterial richness when cultivated with a growth substrate and shade. Our work shows that it is possible to field cultivate biocrust inocula sourced from different deserts, but that community composition shifts toward that of the cultivation site unless habitat amelioration is employed. Future assessments of the function of a mixed inoculum in restoration and its resilience in the face of abiotic stressors are needed to determine the relative benefit of assisted migration compared to the challenges and risks of this approach.

Dryland nitrogen deposition induces microbiome‐driven increases in biocrust respiration and losses of soil carbon

AbstractBiocrusts are a dominant component in drylands worldwide and play critical roles in supporting soil microbial diversity and carbon (C) stocks. Nitrogen (N) fertilization associated with human activities threatens drylands, which are often considered N‐limited ecosystems. Here, we conducted a field experiment in two contrasting soil types (loess vs. sand) to investigate the impacts of low (30 kg N ha−1 year−1) and high (90 kg N ha−1 year−1) fertilization on moss‐biocrust dominated traits, soil nutrients, microbial taxonomic richness, soil C stocks and respiration rates (Rs). We showed that 5 months of N addition resulted in reductions in soil organic C content by 91% and increased both soil microbial richness and diversity. Our results further showed that relative to controls, low levels of N addition increased biocrust Rs by 52% through increased moss biomass and density (38% and 73%) and microbial taxonomic richness and diversity (18% and 23%), while no significant changes in biocrust Rs were observed after high levels of N addition. Considering multiple environmental factors simultaneously, we show that N fertilization indirectly promoted soil respiration and C losses via increases in microbial richness and diversity, which are critical drivers of soil function. Our work provides solid evidence that N deposition, even at low levels of N addition, can result in rapid losses of C in dryland soils. Our findings suggest that to maintain healthy dryland ecosystems and promote C, we must mitigate future land degradation and minimize anthropogenic N deposition.

Unraveling mechanisms underlying effects of wetting–drying cycles on soil respiration in a dryland

Rewetting of dry soils usually stimulates soil carbon (C) emission, a phenomenon known as the Birch effect. Soil C cycling in drylands, which store approximately one third of terrestrial soil organic C (SOC), is strongly affected by wetting–drying cycles. However, the physical, chemical, and biological mechanisms that link rewetting cycles with dryland soil C cycling have not been comprehensively studied, nor do we understand how these mechanisms interact with each other. Here, we conducted a dryland soil incubation experiment manipulating four factors related to global change (soil moisture content, soil moisture variability, C availability, and prior warming) in a factorial design. The experiment was divided into two periods: a rewetting period consisting of six 14-d wetting–drying cycles; and a recovery period lasting 28 days during which soil moisture content was held stable, allowing for examination of the legacy effects of the wet-dry cycles. Rewetting cycles decreased soil aggregate stability under some conditions, but their effects on soil microbial biomass and fungal communities, soil enzyme activities, soil priming, and soil dissolved C were not significant. We found lower average soil respiration under the wetting–drying treatment than the stable soil moisture treatment, and Birch effects were observed, but only under some conditions. This was probably because moisture variability exacerbated soil microbial metabolic stress, which showed itself as oxygen limitation during the initial precipitation pulse and as water limitation during soil drying. Notably, respiration rates remained low even after moisture fluctuations ceased, suggesting a legacy effect of rewetting cycles on dryland microbial communities. Overall, rewetting inhibited aggregate formation (physical mechanism), and suppressed soil respiration by inducing soil microbial metabolic stress (biological mechanism), ultimately leading to lower soil C loss under rewetting. Our findings indicate that Birch effects are mediated by the magnitude of moisture variability, the availability of C, and the degree of physiological stress microbes experience.

Effect of shoot pruning and chicken manure on fruit set and yield of cayenne pepper grown on a sandy dryland soil

Improving the soil properties of a sandy dryland and carbohydrate allocation in crops grown on it is vital for crop production. This study explores the potential benefits of applying chicken manure and shoots pruning on fruit sets and the yield of cayenne pepper (Capsicum frutescens L.) grown on sandy dryland soil. An experiment testing a hybrid variety of cayenne pepper (Dewata 43) was conducted in Gumantar village, North Lombok, Indonesia (8.253654 S, 116.285695 E). Chicken manure treatment consisted of three levels; no chicken manure, chicken manure, and Trichoderma-enriched chicken manure at 3.5 ton ha−1. Pruning consisted of two levels; unpruned and pruned at three weeks after planting. The treatments were arranged factorially in a randomized block design with three replications. The study revealed that the soil was low in organic matter and had low nutrient content. Pruning did not show a significant effect, but chicken manure affected the fruit set and yield of cayenne pepper. Trichoderma-enriched chicken manure produced the highest fruit set (93%) and fruit weight per plant (286 g). The highest yield up to the fifth harvest was much lower than the variety’s yield potential, indicating room for improvement in cayenne pepper production in sandy dryland soils.

Hydrogeology and Hydrogeochemistry of Saline Groundwater Seepage Zones in Wadi Bani Malik Basin, Jeddah, Saudi Arabia: Impacts on Soil and Water Resources

The water seepage zone affects dryland salinity, soil sodicity, land degradation, waterlogging, and rainfall pollution. The priority in terms of the remediation measures was determining the cause of the seepages. Nine water and six soil samples were collected from the Al Tayseer area of the Wadi Bani Malik, Jeddah, Saudi Arabia (SA). The water samples were analyzed for major and toxic metals. For the soil samples, granulometric analysis and infiltration rate analysis were performed. The total dissolved solids (TDS) in water seepages ranged from 1880 to 54,499, whereas boron (B) and iron (Fe) values ranged from 1.9 to 38 mg/L and 0.02 and 0.47 mg/L, respectively. These concentrations were the same for the aquifer in Lake Al Misk, confirming that groundwater infiltration from the lake area was the main reason for the water seepage. The concentrations of silica (Si), aluminum (Al), cobalt (Co), nickel (Ni), zinc (Zn), arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), and lead (Pb) were low, indicating that there was no contamination. The nitrate (NO32−) value ranged from 2.2 to 35 mg/L, indicating agricultural wastewater contribution. According to the granulometric examination, most sediment was sand, followed by gravel, with few fine-grain particles. The infiltration rate ranged from 85 to 864 cm/d, indicating significant leakage. The percentage of ferrugination, ferromagnesian, OH-bearing, and carbonate (CO₃2−) minerals is determined by the 4/2, 5/6, and 6/7 band ratios.

Mapping biocrust distribution in China's drylands under changing climate

Biological soil crusts (biocrusts) are widely distributed in global drylands and have multiple significant roles in regulating dryland soil and ecosystem multifunctionality. However, maps of their distribution over large spatial scales are uncommon and sometimes unreliable, because our current remote sensing technology is unable to efficiently discriminate between biocrusts and vascular plants or even bare soil across different ecosystem and soil types. The lack of biocrust spatial data may limit our ability to detect risks to dryland function or key tipping points. Here, we indirectly mapped biocrust distribution in China's drylands using spatial prediction modeling, based on a set of occurrences of biocrusts (379 in total) and high-resolution soil and environmental data. The results showed that biocrusts currently cover 13.9 % of China's drylands (or 5.7 % of China's total area), with moss-, lichen-, and cyanobacterial-dominated biocrusts each occupying 5.7 % to 10.7 % of the region. Biocrust distribution is mainly determined by soil properties (soil type and contents of gravel and nitrogen), aridity stress, and altitude. Their most favorable habitat is arenosols with low contents of gravel and nitrogen, in climate with a drought index of 0.54 and an altitude of about 500 m. By 2050, climate change will lead to a 5.5 %–9.0 % reduction in biocrust cover. Lichen biocrusts exhibit a high vulnerability to climate change, with potential reductions of up to 19.0 % in coverage. Biocrust cover loss is primarily caused by the combined effects of the elevated temperature and increased precipitation. Our study provides the first high-resolution (250 × 250 m) map of biocrust distribution in China's drylands and offers a reliable approach for mapping regional or global biocrust colonization. We suggest incorporating biocrusts into Earth system models to identify their significant impact on global or regional-scale processes under climate change.

Agroforestry practices impacts on soil properties in the drylands of Eastern Kenya

Agroforestry is one of the land use practices that is perceived to be sustainable and that has beneficial impacts on soil properties. However, as a universal statement, this may not be true as best documented successful agroforestry practices are located largely on good soils. Its impacts on dryland soils have rarely been quantified and studied in detail. This study determined the impacts of selected agroforestry practices on soil properties in Makueni, Eastern Kenya. A total of 252 soil samples were collected along transects located within mixed tree woodlots established in 2007, 2010 and 2013 and adjacent parklands and grazing lands at depths of 0–15 cm, 15–30 cm, 30–45 cm and 45–60 cm. Tree density per agroforestry practice was also determined using the quadrat technique. The soil samples were analyzed using laboratory soil physico-chemical properties techniques. The results showed that Soil Organic Carbon (SOC) and Total Nitrogen (TN) were significantly higher in the woodlots than in the parkland and grazing lands (p ≤ 0.05). SOC was significantly higher in woodlots established in 2007 than those established in 2013 and strongly correlated with the tree density. Phosphorus was significantly higher in parkland as compared to woodlots and grazing lands. Phosphorus and Potassium were significantly higher at 0–15 cm depth compared to other soil depths. bulky density was significantly higher with a corresponding lower total porosity in grazing lands than in the woodlots and parklands. Mixed woodlots positively influenced soil property and could be considered as a strategy to restore degraded dryland soils as well act as important carbon dioxide and nitrogen sinks.

Morchella esculenta cultivation in fallow paddy fields and drylands affects the diversity of soil bacteria and soil chemical properties.

The properties of paddy field (DT) and dry land (HD) soil and food production can be enhanced by the cultivation of Morchella esculenta (ME) during the fallow period. However, whether ME cultivation affects the soil health and microbial diversity of paddy fields and drylands during the cultivation period remains unclear, and this has greatly limited the wider use of this cultivation model. Here, we analyzed the soil chemical properties and bacterial diversity (via metabarcoding sequencing) of DT and HD soils following ME cultivation. Our findings indicated that ME cultivation could enhance soil health. The content of soil phosphorus and potassium (K) was increased in DT soil under ME cultivation, and the K content was significantly higher in HD soil than in DT soil under ME cultivation. ME cultivation had a weak effect on alpha diversity, and ME cultivation affected the abundance of some genera of soil bacteria. The cultivation of ME might reduce the methane production capacity of DT soil and enhance the nitrogen cycling process of HD soil based on the results of functional annotation analysis. Network analysis and correlation analysis showed that Gemmatimonas, Bryobacter, and Anaeromyxobacter were the key bacterial genera regulating soil chemical properties in DT soil under ME cultivation, and Bryobacter, Bacillus, Streptomyces, and Paenarthrobacter were the key taxa associated with the accumulation of K in HD soil. The results of our study will aid future efforts to further improve this cultivation model.

Health Risk Assessment and Environmental Benchmark of Cadmium in Farmland Soils around the Gangue Heap of Coal Mine, Chongqing

To analyze the health risk assessment and environmental benchmark of cadmium in farmland soils surrounding the gangue heap of a coal mine in Chongqing, Hakanson, the ecological risk index and health risk assessment were used. Meanwhile, the soil environmental reference value of the regional cultivated land was inverted based on the species sensitive distribution model (SSD). The results showed that the dryland soil was polluted by Cd, with an over-standard rate of 55.8%, and the paddy field soil was polluted by Cd, with an over-standard rate of 31.6%. The corn was polluted by Cd, with an over-standard rate of 4.4%, and the rice was not polluted by Cd. The Hakanson ecological risk index showed that Cd was mainly characterized in soils by high ecological risk and considerable ecological risk. The health risk assessment indicated that Cd presented low non-carcinogenic risk by corn and rice; however, it showed acceptable carcinogenic risk by corn and unacceptable carcinogenic risk by rice in this study. The sensitivity analysis of health risks showed that the content of Cd was the most sensitive. The SSD inversion showed that the reference values for Cd in dryland soil of pH ≤ 5.5, 5.5<pH ≤ 6.5, 6.5<pH ≤ 7.5, and pH>7.5 had HC5 values of 0.491, 0.382, 0.376, and 0.588 mg·kg-1, respectively, and that for Cd in paddy soil had an HC5 value of 0.807 mg·kg-1. The reverse analysis showed that the HC5 of Cd in dryland soil (pH ≤ 7.5) and paddy soil was relatively relaxed and was higher than the soil risk screening values, which showed that the current standard was relatively loose. However, the HC5 of Cd in dryland soil (pH>7.5) was lower than the soil risk screening values, which showed that the current standard was relatively strict. It is suggested that the current soil standard could be adjusted in this area.

Impact of agricultural management on salts accumulation in dryland soils of central Tunisia

Drylands represent about one-third of the global land and mainly occur in Africa and Asia. Because of the arid conditions, dryland soils are characterized by salt accumulation. Although salt-affected soils are unsuitable for agriculture, some arid lands have been cultivated for a long time. However, especially in the last decades, because of the increasingly warmer climatic conditions and human migration toward favorable environments, a progressive abandonment and degradation of drylands has occurred. Therefore, it is necessary to assess the effects of cultivation on saline soils to develop appropriate soil management techniques to ensure their fertility. This work aims to evaluate the evolution of salinization from currently cultivated soils to soils that have been abandoned for different lengths of time in arid areas of central Tunisia. Morphological and physicochemical properties of the studied soils indicated that the cultivation, through irrigation and the presence of soil cover, reduced salt accumulation in the upper soil horizons. Salt leaching towards deeper horizons and depressed evaporation, which reduced capillary rising, maintained electrical conductivity within tolerable values for most crops. Conversely, the abandonment of previously cultivated fields compromised soil fertility, threatening soil conservation and stabilization of agricultural production in the medium to long term.

Under flooding conditions, controlled-release fertiliser coated microplastics affect the growth and accumulation of cadmium in rice by increasing the fluidity of cadmium and interfering with metabolic pathways

The combined pollution of microplastics (MPs) and Cd can affect plant growth and development and Cd accumulation, with most studies focusing on dryland soil. However, the effects of polyurethane (PU) controlled-release fertiliser coated MPs (PU MPs), which widely exist in rice systems, coupled with Cd on plant growth and Cd accumulation under flooding conditions are still unknown. Therefore, in the present study, in situ techniques were used to systematically study the effects of PU MPs and Cd coupling on the physiological and biochemical performance, metabolomics characteristics, rhizosphere bacterial community, and Cd bioavailability of rice in different soil types (red soil/cinnamon soil). The results showed that the effects of PU MPs on rice growth and Cd accumulation were concentration-dependent, especially in red soil. High PU concentration (1 %) inhibited rice root growth significantly (44 %). The addition of PU MPs inhibited photosynthetically active radiation, net photosynthesis, and transpiration rate of rice, mainly with low concentration (0.1 %) in red soil and high concentration (1 %) in cinnamon soil. PU MPs can enhance the expression of Cd resistance genes (cadC and copA) in soil, enhance the mobility of Cd, and affect the metabolic pathways of metabolites in the rhizosphere soil (red soil: fatty acid metabolism; cinnamon soil: amino acid degradation, heterobiodegradation, and nucleotide metabolism) to promote Cd absorption in rice. Especially in red soil, Cd accumulation in the root and aboveground parts of rice after the addition of high concentration PU (1 %) was 1.7 times and 1.3 times, respectively, that of the control (p < 0.05). Simultaneously, microorganisms can affect rice growth and Cd bioavailability by affecting functional bacteria related to carbon, iron, sulfur, and manganese. The results of the present study provide novel insights into the potential effects of PU MPs coupled with Cd on plants, rhizosphere bacterial communities, and Cd bioavailability.

Analysis on Change in Soil Organic Carbon Content of Farmland in Yangtze River Economic Belt Under Different Fertilizing Measures

The literature from a long-term fertilization experiment in the Yangtze River Economic Belt from January 1992 to May 2022 was collected, and the data of farmland soil organic carbon were extracted and integrated. Using the normalization treatment and the analysis method of relative annual variation, the overall change in soil organic carbon content in farmland in the Yangtze River Economic Belt under different long-term fertilization measures was studied, and the change differences of soil organic carbon content under three tillage modes were compared so as to judge and analyze the influence of the duration of the experiment on soil organic carbon dynamics. The results showed that under different long-term fertilization measures, the organic carbon content of farmland soil in the Yangtze River Economic Belt in China showed an overall upward trend. The NP, NPK, O, and NPKO treatments all increased the organic carbon content of agricultural soils, with that of the NPKO treatment being the largest. The sole application of inorganic nitrogen fertilizer reduced the organic carbon content of the soil. The rates of change in soil organic carbon content were 0.22 g·(kg·a)-1, 0.24 g·(kg·a)-1, and 0.16 g·(kg·a)-1for dryland, paddy, and water-dry rotation farmland, respectively. Additionally, the relatively rapid increase effect of organic carbon brought by the O and NPKO treatments could last for no more than 28 years in dryland soil but could still last for more than 28 years in paddy field and paddy-upland rotation soil. There was some variation in the rate of change of soil organic carbon content between soil types. The average rate of change of organic carbon was 0.25 g·(kg·a)-1for red soils, 0.14 g·(kg·a)-1 for brown soils, 0.19 g·(kg·a)-1 for tidal soils, and 0.15 g·(kg·a)-1 for rice soils. The trend of NPKO>O>NPK>NPK>NP>N was basically maintained for the rate of change in soil organic carbon content. The NPKO treatments were all significantly higher than the chemical fertilizer (N, NP, and NPK) treatments alone. The N treatment showed a reduction in organic carbon content in both red soil and rice soils. Considering the carbon fixation of farmland soil, the combined application of organic and inorganic fertilizers is a more suitable fertilization method in this area.

Biochar, manure and superabsorbent improve the physical quality of saline‐sodic soil under greenhouse conditions

AbstractThe increasing salinization and sodification of soils in drylands and irrigated systems present a great challenge to agricultural production and threaten soil quality. There is an urgent need to investigate potential strategies to remediate soils that are threatened by these processes. To address this challenge, the current study investigated the effects of organic and inorganic amendments and leaching fraction (LF) on physical and hydraulic properties including the soil water characteristic curve (SWCC), Dexter's index of soil physical quality (SDexter), bulk density (BD), saturated hydraulic conductivity (Ks), and water repellency index (RI) in a saline‐sodic soil. A greenhouse experiment was carried out in a completely randomized design with two factors (amendment and LF). The amendments included superabsorbent (1%) (SA), zeolite modified with CaCl2 (2%) (ZC), biochar (2%) (B), biochar + manure (2%) (BM), and a control (no amendment) (CT), and combined with two levels of LF (15% and 30%). Spring wheat (Triticum aestivum, ‘UG99’) was planted in the soil columns. After harvest, undisturbed samples were collected from each column for the determination of soil properties. The results demonstrated the effectiveness of the SA and organic amendments to enhance Ks and decrease BD. There was a significant (p &lt; 0.01) positive effect of the amendments, particularly biochar and superabsorbent on the soil pore size distribution. The SA amendment significantly increased soil water retention, especially at high matric potentials (i.e., 0 to −80 hPa). The effect of organic amendments on the SWCC was in between those of the ZC and SA amendments. The SA and BM treatments were sub‐critically water repellent, while the ZC treatment increased soil water repellency. The SA, B, and BM15 treatments exhibited very good physical quality (SDexter &gt; 0.05). The relative air and moisture capacities were optimal in the B‐amended soil at field capacity (matric potential –330 hPa). We conclude that B, BM, and SA are suitable amendments for reducing the adverse effects of salinity and sodicity via an improvement in soil physical quality.

Empirical equations for estimating field capacity in dryland cropping soils of southeastern Australia

The root zone soil water content at field capacity, θFC, is often crucial for irrigation scheduling and soil-plant-atmosphere modelling. Although θFC is traditionally determined using methodologies based on matric head or when water flux at the bottom of the root-zone equal to a prescribed negligible flux, these approaches can be problematic for some soils and applications. In this study, a novel water storage approach was used to estimate θFC for 11 soil texture classes in southeastern Australia (northwest Victoria) by employing the Soil-Water-Atmosphere-Plant (SWAP) model to simulate gravity drainage from saturation in the active root zone (top 60 cm). Field capacity was specified as the average root zone water content corresponding to a 1% relative change in daily soil water storage. We have also estimated flux-based θFC when prescribed flux at the bottom of the root-zone was 0.1 cm d-1. Three new empirical equations were developed to estimate storage-based θFC as a function of SWAP-simulated drainage flux out of the root zone, the n parameter of the van Genuchten function, and the saturated soil hydraulic conductivity, Ks, or the soil water content at − 100 cm matric head. We have evaluated these three new equations in addition to nine published equations for estimating θFC. The three new equations were found to be better predictors of θFC than most of the nine popular equations reported in the literature when compared to flux-based θFC values. Based on findings from this study the new equations are considered to be effective for irrigation scheduling and crop/climate modelling on the dryland soils of Victoria. Future studies will assess the applicability of the new equations to other parts of Australia.

The synergy of dark septate endophytes and organic residue on Isatis indigotica growth and active ingredients accumulation under drought stress

Drought is a major abiotic stress factor affecting plant growth and production, while utilizing beneficial endophytic fungi is one of the most promising strategies for enhancing plant growth and drought tolerance. In the present study, a pot experiment was conducted to investigate the beneficial effects of dark septate endophytes (DSE) (Acrocalymma aquatica and Alternaria alstroemeriae) combine with organic residues from sterilized or non-sterilized fermented corn straw by Trichoderma afroharzianum on the growth and drought resistance of Isatis indigotica. Drought stress (30% field water capacity) reduced the shoot biomass, root biomass, and epigoitrin content of I. indigotica by 34.30%, 80.85%, and 16.51%, respectively. The DSE inoculation alone increased shoot biomass and epigoitrin content under well-watered condition (70% field water capacity) by 13.75%− 65.98% and 52.33%− 67.59%, respectively, and shoot biomass under drought stress by 37.27%− 84.91%. The organic residues application alone increased root biomass under well-watered condition and drought stress by 71.88%− 107.06% and 463.61%− 678.69%, respectively. The mixed application of DSE and organic residues increased root biomass and epigoitrin content under well-watered condition by 66.79%− 144.66% and 89.02%− 136.63%, respectively, and under drought stress by 410.66%− 580.49% and 28.26%− 88.37%, respectively. Structural equation modeling demonstrated that DSE inoculation, organic residue application, and the mixed application improved the growth of I. indigotica under drought stress through different direct and indirect pathways. Variation partitioning showed that DSE was the primary factor improving the epigoitrin content, and organic residue was the primary factor influencing plant biomass and morphological parameters. The mixed application of DSE and organic residue had further synergistic effects on soil enzyme activities, soil organic matter, root biomass, and epigoitrin content, especially the mixed application of A. aquatica and sterilized organic residue. These results contribute to a further understanding of the ecological function of DSE in dryland soils and reveal the synergistic application value of DSE and organic residue for medicinal plant cultivation.

Assessing a multi-method approach for dryland soil salinization with respect to climate change and global warming – The example of the Bajestan region (NE Iran)

Dryland soil salinization strongly affects soil properties, with severe consequences for regional ecology, agriculture and the aeolian dust dynamics. Given its climate-sensitivity it forms a serious environmental hazard, and to cope with this challenge during current global warming it needs to be better understood. The Bajestan Playa in the strongly salinization-affected Iranian drylands hosts several protected areas and forms an important regional dust source. Hence, soil salinization in this region affects local and regional ecosystems and societies, but was not systematically studied yet. Using an unprecedented comprehensive approach we systematically monitored regional soil salinity 1992–2021 using remote sensing as well as on-site field and laboratory measurements, and linked these with regional and global climatic data to understand (i) the spatio-temporal soil salinity dynamics, (ii) the impact of regional and global climate changes, and (iii) the potential of our approach for further soil salinity studies.Our annual time resolution over three decades provided significantly deeper and unprecedented insights into soil salinization: Both regional annual precipitation and temperature control soil salinity, but the latter responds to precipitation with time lags of up to two years and to higher temperatures without any time lag. This probably reflects the transport time of leached soluble salts from their sources following humid years. No systematic soil salinity changes were observed within the playa basin, but outside the basin soil salinity systematically increased. Whereas regional precipitation did not show a systematic trend during the last decades, regional temperature increased and was mostly correlated with the increasing GLOTI, POL and TSA climatic indices. Hence, given ongoing global warming a further increase of regional soil salinization should be expected, with serious consequences for saline dust emissions, the regional protected areas and climate-related migrations. Altogether, our multi-disciplinary pioneer study demonstrates a high future application potential also for other salinity-affected drylands, forming a base to deal with the consequences of ongoing global climate change.

Biochar as a carbonaceous material to enhance soil quality in drylands ecosystems: A review

Drylands are fragile environments that should be carefully managed to improve their quality and functions to achieve sustainable development. Their major problems involve low availability of nutrients and soil organic carbon content. Biochar effect on soil is a joint response of micro to nano sized biochar and soil characteristics. In this review, we attempt to carry out a critical analysis of biochar application to enhance dryland soil quality. Correlating the effects identified from its soil application, we explored the subjects that remains open in the literature. The relation of composition-structure-properties of biochar vary among pyrolysis parameters and biomass sources. Limitations in soil physical quality in drylands, such as low water-holding capacity, can be alleviated by applying biochar at a rate of 10 Mg ha−1 also resulting in beneficial effects on soil aggregation, improved soil porosity, and reduced bulk density. Biochar addition can contribute to the rehabilitation of saline soils, by releasing cations able to displaces sodium in the exchange complex. However, the recovery process of salt-affected soils might be accelerated by the association of biochar with another soil conditioners. This is a promising strategy especially considering the biochar alkalinity and variability in nutrients bioavailability to improve soil fertilization. Further, while higher biochar application rate (>20 Mg ha−1) might change soil C dynamics, a combination of biochar and nitrogen fertilizer can increase microbial biomass carbon in dryland systems. Other aspect of biochar soil application is the economic viability of scale-up production, which is mainly associate to pyrolysis process being biochar production the costliest stage. Nevertheless, the supplying of feedstock might also represent a great input on biochar final costs. Therefore, biochar-based technology is a big opportunity to improve fragile environments such as drylands, integrating sustainable technologies with regional development. Considering the specificity of application area, it might be a model of sustainable agricultural practices protecting the environment in a bioeconomic perspective.

Effects of Biochar and Organic Additives on CO2 Emissions and the Microbial Community at Two Water Saturations in Saline–Alkaline Soil

The nutrient-limiting conditions in saline–alkali soil as well as the salinity and alkalinity stress are successfully alleviated by water management measures and the addition of organic matter. However, the impacts of these two strategies on the microbe-driven CO2 emissions in saline–alkaline soils are not yet clear. Therefore, a 150-day incubation experiment was conducted in this study to evaluate the short-term effects of water regulation and the addition of organic matter with different characteristics on CO2 emissions and microbial community characteristics in saline–alkali soils under non-flooding conditions. This study was conducted at two water saturations, i.e., 50% WFPS and 80% WFPS. In addition, five organic matter treatments were conducted: CK: control; N: urea; SN: Straw + urea; SNH: Straw + urea + microbial agent; and SNB: Straw + urea + biochar. The results demonstrated that compared with 50% WFPS, 80% WFPS significantly increased cumulative CO2 emission by 27.66%, but significantly decreased salt content and the fungal Chao1 and Shannon indices. The application of the biochar and microbial agent decreased the cumulative CO2 emissions of the SN treatment by 27.39% and 14.92%, respectively. When sufficient carbon supply is available, the decrease in fungal diversity may reduce CO2 emission. The findings demonstrated that SNH and SNB at 80% WFPS might decrease CO2 emissions under straw carbon intake as well as the loss of labile organic carbon (LOC). Additionally, these treatments can alleviate microbial stress caused by salinity, which has a favorable impact on enhancing carbon storage in salinity-affected dryland soils.

Direct evidence and mechanism for biocrusts-induced improvements in pore structure of dryland soil and the hydrological implications

As a crucial living skin inhabiting the soil-atmosphere interface, biocrusts play a vital role in various soil properties and processes, especially surface soil pore structure and soil pore-related hydrological processes, such as infiltration and evaporation. However, it remains unclear how biocrusts affect pore structure in the micrometric point of view. In this study, X-ray computed tomography and image analysis were employed to quantify the differences in soil pore structure between bare soil and three types of biocrusts (cyanobacterial, cyanobacterial-moss mixed, and moss crusts) at 0–50 mm depth. Three-dimensional images were segmented and analyzed to assess morphological and geometrical properties, such as porosity, pore volume, degree of anisotropy, Euler number, pore shape, pore connectivity, and pore tortuosity. Our results showed that the porosity of three types of biocrusts was, on average, 100% higher than bare soil, and the porosity ranked in order of moss crusts > mixed crusts > cyanobacterial crusts > bare soil. In comparison to bare soil, pore surface area density, mean pore volume, and node density of biocrusts were increased by 45%, 422%, and 52% on average, respectively. Biocrusts had larger fractal dimensions but lower degrees of anisotropy, mean tortuosity, and Euler number, which indicates the pore structure of biocrust became more complex and stable with higher connectivity compared to bare soil. Additionally, elongated pores had the largest contribution to porosity, and these pore proportions were significantly higher in biocrusts than bare soil. More importantly, the pore network model and network analysis revealed that biocrusts have a higher connected porosity (17% vs. 4%), connected porosity/isolated porosity (11.7 vs. 0.6), average coordination number (8 vs. 5), and number of channels (14,480 vs. 807), but a lower average channel length (2.7 vs. 3.8 mm), which indicates that the physical and topological structures of pore network in biocrusts were reconfigured and exhibited a better pore network connectivity. Moreover, the biocrusts increased soil water holding capacity by 87% on average, but decreased saturated hydraulic conductivity by 55% as compared to bare soil. From the reshaped pore structure, improved soil water holding capacity, and decreased infiltrability of the biocrusts in comparison to bare soil, we conclude that biocrusts play a vital role in surface soil water balance, which subsequently affect surface hydrological processes (e.g., runoff generation and evaporation) in drylands.