Deep Soil Profiles Research Articles

Land-use change affects stoichiometric patterns of soil organic carbon, nitrogen, and phosphorus in the red soil of Southeast China

Soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) play a vital in plant growth, and their stoichiometric ratios (RCN, RCP, RNP, and RCNP) are important indicators of the elemental balance in the soil ecosystem. However, the effects of land-use change (from natural forest to high-intensity orchards) on dynamics of SOC, TN, TP, and their stoichiometric ratios along the deep soil profile remain poorly understood, especially in the red soil of Southeast China. Therefore, in the present study, we selected the high-intensity managed pomelo orchard systems (7-year-old and 20-year-old) of Pinghe County developed from the natural forest and investigated their soil nutrients distribution and stoichiometric ratios at a depth of 0–200 cm. We found that conversion of natural forest into highly managed pomelo orchard systems effectively increased the SOC (5.01 to 9.05%), TN (98.80 to 126.79%), and TP (507.50 to 1914.65%) contents in the depth of 0–20 cm. On the contrary, in this same depth, RCP and RNP consistently decreased with increasing planting years, while no significant differences were found in RCN between 7-year-old and 20-year-old pomelo orchards. Nonetheless, planting year affected the SOC, TN, RCN, and RCP in the deep soil at 0–200 cm, while TP and RNP at 0–80-cm soil depth. These findings strengthen our understanding of soil nutrients and stoichiometry changes as a result of land-use change and could also provide a vital resource for the evaluation of different land uses.

Roots take up labeled nitrogen from a depth of 9 m in a wooded savanna in Brazil

The savannas (called Cerrado) are the second-largest vegetation formation in Brazil after the Amazon rainforest, with about 2 million km2. Roots have been found in very deep soil layers in Cerrado ecosystems, which suggests a crucial role of deep rooting in the supply of water and nutrients over dry periods. The aim of our study was to gain insight into the complementarity of common Cerrado woody species in taking up mobile nutrients throughout deep soil profiles. In a closed-canopy savanna with dense woody understory, labeled nitrate was injected into the soil at six soil depths (0.1, 1.5, 3.0, 6.0, 9.0, or 12.0 m) with three plots per depth, at two dates (in rainy and dry seasons). Five months after labeled nitrate injection, young leaves were sampled and foliar δ15N was determined in each plot in the three most common woody species (Coussarea hydrangeifolia, Miconia albicans and Xylopia aromatica). The maximum depth of 15N uptake was dependent on the species. X. aromatica trees took up 15N from a maximum depth of 9 m and exploited a much larger soil volume than the two other species, with the uptake of 15N at a horizontal distance of up to 5 m between the trunk and the injection site. The behavior of M. albicans and C. hydrangeifolia was similar, with a strong uptake of 15N only in the 0–1.5 m soil layer, within 2 m horizontally from the injection site. The depth of 15N uptake over the dry season was not related to the diameter at breast height of the woody plants sampled. We show that roots can take up labeled nitrogen from a depth of 9 m in tropical wooded savannas, which suggests an important role of deep-rooted species in closing biogeochemical cycles on highly weathered tropical soils.

Direct Seeding and Transplanting Influence Root Dynamics, Morpho-Physiology, Yield, and Head Quality of Globe Artichoke.

The objective of this two-year field study was to assess the influence of stand establishment methods (direct seeding or transplanting) on root growth dynamics, shoot morphology, leaf physiology, yield, and quality of globe artichoke (Cynara cardunculus). Three artichoke cultivars were evaluated, ‘Green Globe Improved’ (GGI), ‘Imperial Star’ (IS), and ‘Romolo’ (ROM). Plants established with the transplanting method had higher mean root length intensity (La), root length, and root surface area as compared to plants established by direct seeding. The topsoil (0–20 cm) had on average higher La, root length, and root surface area than deeper soil profiles. Transplanted plants had higher plant shoot width and leaf area index (LAI) chlorophyll content index (SPAD) than direct seeded plants at the vegetative stage in 2015. The improvement of root and shoot growth in transplants (compared to direct seeding) also resulted in higher (p < 0.05) marketable yield (21.1 vs. 19.9 ton ha−1 in 2015 and 18.3 vs. 13.7 ton ha−1 in 2016). Additionally, 46–50% of the total yield occurred during the first 30 days of harvest in the transplanting method compared to 13–38% for direct seeding. No significant differences were found between planting methods or cultivars in leaf-level gas exchange (photosynthesis, stomatal conductance, and transpiration) and cynarin concentration in the marketable heads. Although chlorogenic acid was similar in both establishment methods in 2015, direct seeding had higher concentration in 2016. Comparing cultivars, GGI had higher root length, surface area, root volume, and earlier and higher marketable yield than ROM. However, ROM had higher mean root length intensity (La; total root length per specific area in soil profile) than GGI in both growing seasons. This study showed significant and consistent improvements in root and shoot traits, and yield for transplants as compared to direct seeded plants.

Shrubs magnify soil phosphorus depletion in Tibetan meadows: Conclusions from C:N:P stoichiometry and deep soil profiles

Globally, the proliferation of shrubs within grasslands stimulates soil phosphorus (P) cycling and increases topsoil P storage beneath their canopies. However, little is known regarding the impact of shrub encroachment on subsoil P storage, and whether shrubs mediate changes in soil stoichiometry, like increasing P cycling. In grazed meadows on the Tibetan Plateau, soil and roots were sampled to 1 m depth in shrubby Hippophae rhamnoides ssp. sinensis groves and the surrounding grassy areas. Shrubs had higher P content than grasses, but lower C:P ratios in their leaves, litter, and roots. Similarly, shrubs had higher microbial P content than grasses, but lower microbial biomass C:P and N:P ratios in the soil. The larger microbial P stock in the 1 m of soil beneath shrubs responded to the larger root P stock there as well. Thus, both the plants and microbes acquired more P in shrubby areas than in grassy areas by accelerating P mineralization. The greater net production of available P in the topsoil and the synthesis of microbial P throughout the profile under shrubs increased the P solubility. Total P, inorganic P, and organic P stocks were lower under shrubs than under grasses in the top 1 m of soil. This decrease in soil P storage beneath shrubs is most likely attributable to P leaching due to higher P solubility, heavy rainfall, and larger soil gaps. Moreover, shrubs also had larger plant biomass P stock compared to grasses, and thus the depletion of P from the top 1 m of soil was further magnified via plant biomass removal. We concluded that shrubs increase P cycling to overcome the stoichiometric imbalance between their P requirement and the supply in the soil, and the fast P cycling under shrubs magnify P depletion within the rooted soil depth in alpine meadows.

High Nitrate Accumulation in the Vadose Zone after Land-Use Change from Croplands to Orchards

Additional evidence indicates that the nitrate stored in the deep soil profile has an important role in regulating the global nitrogen (N) cycle. This study assessed the effects of land-use changes from croplands to intensive orchards (LUCO) on N surplus, nitrate accumulation in deep soil, and groundwater quality in the kiwifruit belt of the northern slope region of the Qinling Mountains, China. LUCO resulted in comparatively high N surplus in orchards (282 vs 1206 kg ha-1 yr-1, respectively). The average nitrate accumulation within the 0-10 m profiles of orchards was 7113 kg N ha-1, which was equal to approximately the total N surplus of 6 years of the orchards. The total nitrate stock within 0-10 m soil profiles of the kiwifruit belt was 266.5 Gg N, which was 3.5 times higher than the total annual N input. The nitrate concentrations of 97% of groundwater samples exceeded the WHO standard. The LUCO resulted in large nitrate storage in the vadose zone and caused serious contamination of groundwater. Our study highlights that nitrate accumulation in the vadose zone of an intensive land-use system is one of the main fates of surplus N and also a hotspot of nitrate accumulation.

Root-based Responses of Well-watered and Water-stressed Chickpea (Cicer arietinum L.) Genotypes Varying for Drought Tolerance and Biomass

Background: Chickpea is a pivotal grain legume crop and is grown in rain-fed conditions where its production has been challenged by drought. Methods: To understand precisely the root-based responses to well-watered (WW) and water-stressed (WS) treatments, 14 chickpea (Cicer arietinum L.) genotypes differing in drought tolerance and biomass were studied in 100-cm cylinders under glasshouse conditions. Result: The genotypes exhibited significant variations in rooting depths ranging from 84.5 to 100.3 cm and 78.7 to 121 cm in WW and WS treatments, respectively and root biomasses varied from 0.23 to 1.01 g and 0.38 to 0.91 g. The average root biomass of drought-tolerant genotypes was 61.3% in WS treatment and 64.4% in WW treatment higher than that of drought-sensitive genotypes. Moreover, genotype with high biomass revealed greater root biomass and deeper rooting than the genotype with low biomass in both treatments. The root biomass in the deeper soil profile differed between drought-tolerant and drought-sensitive genotypes and was generally greater in WS compared to WW treatment. Overall, screening the variability in root features of chickpea genotypes with varying levels of drought tolerance and biomass contributes to new insights for understanding drought adaptation mechanisms and the improvement of new cultivars with superior root traits in breeding programs.

Vertical distribution and regulation of Olsen-phosphorus in 6-m soil profiles after farmland-to-apple orchard conversion on the Chinese Loess Plateau

Data on the dynamics of Olsen-P in deep soil profiles are crucial for improving P use efficiency but remain scarce worldwide. Hence, we sampled sixty 6-m-deep soil profiles from farmland and in 8-yr, 17-yr, and 25-yr-old apple orchards on China’s Loess Plateau, and aimed to investigate the vertical distribution of soil Olsen-P following the farmland-to apple orchard conversion. Land-use change from farmland to apple orchard significantly affected Olsen-P at 0–40 cm soil, with the concentration generally increasing with age of apple orchard. By contrast, Olsen-P at 40–600 cm was not significantly different among the cropping systems. In both farmland and apple orchards, the concentration of Olsen-P decreased at 40–100 cm, compared with that in the 0–40 cm layer, increased with depth from 100 to 400 cm and then stabilized from 400 to 600 cm. The highest accumulation of residual soil Olsen-P in the 6-m profile (RSP0−600) was in the 25-yr orchard, followed by the 17-yr and 8-yr orchards, with the lowest accumulation in farmland. The differences in RSP0−600 cm were primarily associated with RSP0−100 cm, which was significantly positively related to the accumulative application of P fertilizer. The change point in soil Olsen-P against P leaching was 71.2 mg kg−1, but in farmland and 8-yr, 17-yr, and 25-yr apple orchards, the averaged-depth contents of Olsen-P were all below the critical value, indicating no P leaching risk. Regression analysis revealed that the vertical distribution of soil Olsen-P was regulated by P fertilization at 0–100 cm and by crop roots at 100–600 cm, irrespective of cropping system. The insights gained on Olsen-P accumulation and migration within deep soil profiles after the farmland-to-apple orchard conversion can help to optimize land use and P fertilization management in major apple-producing countries with burgeoning growth in apple production.

Vertical distribution of soil available phosphorus and soil available potassium in the critical zone on the Loess Plateau, China

Soil available phosphorus (SAP) and soil available potassium (SAK) are important elements in the growth of plants. However, limited data are available regarding the vertical distribution of SAP and SAK in deep soil profiles. In this study, we investigated the vertical variations in SAP and SAK in the critical zone on the Loess Plateau (50–200 m), China, by using classical statistical and geostatistical methods. The soil samples were collected from the top of the soil profile down to the bedrock by soil core drilling at five typical sites. SAP decreased throughout the profile. Whereas the SAK exhibited an increasing trend at all sites. The mean SAP concentration ranged from 0.94 to 32.56 mg kg–1 at the sampling sites and the SAK concentration ranged from 44.51 to 229.31 mg kg–1. At all of the sampling sites, SAK was significantly positively correlated with the depth and clay content, but there was a significantly negative correlation between the SAK and the sand content. The exponential model could fit most variograms of SAP and SAK at all sampling sites. The results obtained in this study to improve our comprehension of the SAP or SAK distribution conditions on the Loess Plateau, which is important for reasonable fertilizer application and vegetation planting practices.

Availability of soil base cations and micronutrients along soil profile after 13-year nitrogen and water addition in a semi-arid grassland

Alteration in the availability of soil base cations and micronutrients is critical to maintain stable ecosystem functioning under the predicted global change scenarios. However, changes in these soil cations and their relationships with soil physiochemical properties along soil profile remain unclear under the combined increasing N deposition and precipitation changes. In this study, the concentrations of soil exchangeable base cations (Ca, Mg, K and Na) and available micronutrients (Fe, Mn, Cu and Zn) were determined along an 80-cm soil profile after 13-year continuous N and water manipulation in a semi-arid grassland. Our results showed that N addition significantly decreased exchangeable Ca (− 25.4%, averaging across the three N addition rates) and Mg (− 7.8%) at the depth of 10 cm while increased available Fe (+ 70.5%), Mn (+ 64.7%), and Cu (+ 26.0%). Besides, the magnitude of the increase or decrease escalated with the rates of additional N. Such pattern was also true for the concentrations of available Fe, Mn and Cu in the 10–20 cm soil layer, but the magnitude of changes was much smaller than in the top 10-cm soil layer. Nevertheless, N addition increased the concentrations of the three available micronutrients across the entire profile, indicating that Fe, Mn and Cu were more sensitive to N addition in subsoils than surface soils. Nitrogen addition significantly reduced soil cation exchange capacity (CEC) in the top 10-cm and soil base saturation (BS) ratio in the top 20-cm soil, while water addition significantly increased soil CEC and BS ratio in the top 20-cm soil. Water addition significantly increased Na (+ 75.1%) in the entire soil profile and increased Ca (+ 14.8%), Mg (+ 12.7%) at the 0–10, 10–20 and 40–60 cm soil layers. Soil pH positively correlated with soil exchangeable Ca, Mg and Na, but negatively with available Fe, Mn and Cu in the upper 20 cm. Soil base cations and CEC positively correlated with clay and silt contents, but negatively with sand content along the profile. These results can extend our understandings on soil cation dynamics to deep soil profile under long-term N and water addition and suggest that precipitation effects should be considered when assessing N deposition effects on these soil cations.

Effect of Eucalyptus Globulus Woodlot Plantation on Selected Soil Physico-Chemical Properties, Wheat Yield in Wogera District, Amhara Region, Ethiopia

Currently, a Eucalyptus globule is a common smallholder plantation species in the Wogera district. The species is significantly expanding on marginal and fertile farmlands. The objective is to analyze the effects of Eucalyptus globules woodlots plantation and their directions on selected soil physicochemical properties and yield of wheat crop. Three woodlots with similar site conditions were selected for this particular study. Soil samples were taken at a soil depth of 20 cm in RCBD design with three replications. Soil samples were taken at four directions (East, West, South, and North) of woodlots plantation at five different horizontal distances from the woodlots; the center of the woodlot, 5 m, 10 m, 15 m, and 40 m. For the wheat yield study: quadrates of 1m2 area at each distance within directions were laid for wheat grain yield measurement. The finding indicated that electric conductivity, available phosphorus, cation exchange capacity, soil texture, and exchangeable cations were not significantly different across the different directions and distances, whereas soil bulk density, pH, total nitrogen, organic matter were significantly different. This could be attributed to the high organic matter addition via litter-fall, root biomass, uptake, and return of nutrients from deeper soil profiles under the tree canopies. The biomass and grain yield of wheat were significantly different across distance and direction from the sampled woodlot in increasing trend in all directions, this study recommends Eucalyptus should planting on marginal lands with appropriate distance from croplands about 20m to minimize its effect on crop yields.

Anthropogenic Pb contribution in soils of Southeast China estimated by Pb isotopic ratios

Isotopic ratios were used to identify the source of Lead (Pb) contamination in rural soils from Southeast China. Enrichment of Pb in surface soils was detected from three sampling locations, with the 206Pb/207Pb ratio indicating recent anthropogenic input. The 206Pb/207Pb ratio from deeper soil profiles reflected the ratio from parent basalt. Mass fractions of anthropogenic-derived Pb for soil samples in the upper profiles was as high as 50%, implying that surface soils in the current study were impacted by anthropogenic activity. The 206Pb/207Pb and 208Pb/206Pb ratios were similar to anthropogenic sources including the combustion of coal, which has been common practice in the region for 2500 years. Considering the relatively short history of petroleum use in this area and the rural location of soils, anthropogenic Pb source from coal burning was considered to be the main cause of lead pollution.

No-till and carbon stocks: Is deep soil sampling necessary? Insights from long-term experiments

Confusion persists regarding the potential for no-till (NT) farming to accumulate soil organic C (SOC) and mitigate climate change. This uncertainty could be partly due to shallow sampling (<40 cm soil depth) employed in most previous SOC publications. The specific objective of this study was to gain additional knowledge of SOC accumulated by a wide range of tillage systems in surface and deeper soil profiles in the long term (> 34 yr). We quantified SOC stock (Mg ha−1) on an equivalent mass basis for the 0–60 or 100 cm soil depths for NT, disk, double disk, chisel plow, and moldboard plow under continuous corn and corn-soybean on silt clay loams after 34 yr and 39 yr in the western US Corn Belt. Results showed that NT did not increase SOC stocks near the surface but it did with cumulative depth relative to moldboard plow. No-till accumulated SOC at a rate of 0.68 Mg ha−1 yr-1 relative to inversion tillage (moldboard plow). However, NT did not store more SOC than common conventional (chisel plow) or reduced (disk) till practices for the whole soil profile. Results indicate that depth of soil sampling can affect conclusions about tillage system impacts on SOC stocks. For example, if we had sampled to 20 cm soil depth only, we would have incompletely concluded that NT does not significantly accumulate more SOC than moldboard plow. Results after 34 and 39 yr of tillage management also indicate that non-inversion tillage, particularly disk, can be as effective as NT for accumulating SOC. Overall, deep soil sampling can tell a different story about NT impacts on SOC stocks from shallow sampling.

A RECENT GEOMORPHIC AND PEDOLOGICAL STUDIES ON MENOUF PROVINCE SOILS, MENOUFIA GOVERNORATE, EGYPT

The current work was performed in 2018 aiming to study the geomorphological and pedological characteristics as well as classification and capability evaluation for soils of Menouf province area, Menoufia governorate, Egypt. The integration of Remote Sensing (RS) and Geographic Information System (GIS) techniques was used to achieve this work. The geomorphic map produced by processing and identifying the Landsat image using RS and GIS technology indicated that, the main landscape unit in the studied area is Alluvial Plain includes nine landforms namely: high terraces (19.4% of the studied area), medium terraces (15.3%), low terraces (24.6%), over flow basin (25.6 %), decantation basin (7.9%) in addition to meandering belt, depression, levee, and island (with small areas). Twenty-four soil profiles were chosen to represent the different landforms.The land and site features are observed and registered. The soil profiles were dug, morphologically described, and then samples were collected representing the subsequent layers in each profile for integrated physical and chemical analyses. The studied area has almost flat topography with deep soil profiles and freely well drained. These soils have loam to sandy clay loam texture with moderate medium sub angular to angular blocky structure. The analytical data revealed that, the studied soils are moderately alkaline, non-saline and haven’t sodicity effect. The soils are slightly calcareous having very slight gypsum content. Organic matter (OM) is lowand decreases with depth. The cation exchange capacity (CEC) is correlated to the fine fractions and OM contents in these soils. The studied soil profiles haven't any diagnostic horizons, therefore they were classified up to sub great group level under Entisols order mainly as Typic Torriorthents. The land capability evaluation indicated that, about 48% of the studied soils have a Good capability class (C2) and the rest (52%) are considered as a Fair (C3) one.

A RECENT GEOMORPHIC AND PEDOLOGICAL STUDIES ON MENOUF PROVINCE SOILS, MENOUFIA GOVERNORATE, EGYPT

The current work was performed in 2018 aiming to study the geomorphological and pedological characteristics as well as classification and capability evaluation for soils of Menouf province area, Menoufia governorate, Egypt. The integration of Remote Sensing (RS) and Geographic Information System (GIS) techniques was used to achieve this work. The geomorphic map produced by processing and identifying the Landsat image using RS and GIS technology indicated that, the main landscape unit in the studied area is Alluvial Plain includes nine landforms namely: high terraces (19.4% of the studied area), medium terraces (15.3%), low terraces (24.6%), over flow basin (25.6 %), decantation basin (7.9%) in addition to meandering belt, depression, levee, and island (with small areas). Twenty-four soil profiles were chosen to represent the different landforms.The land and site features are observed and registered. The soil profiles were dug, morphologically described, and then samples were collected representing the subsequent layers in each profile for integrated physical and chemical analyses. The studied area has almost flat topography with deep soil profiles and freely well drained. These soils have loam to sandy clay loam texture with moderate medium sub angular to angular blocky structure. The analytical data revealed that, the studied soils are moderately alkaline, non-saline and haven’t sodicity effect. The soils are slightly calcareous having very slight gypsum content. Organic matter (OM) is lowand decreases with depth. The cation exchange capacity (CEC) is correlated to the fine fractions and OM contents in these soils. The studied soil profiles haven't any diagnostic horizons, therefore they were classified up to sub great group level under Entisols order mainly as Typic Torriorthents. The land capability evaluation indicated that, about 48% of the studied soils have a Good capability class (C2) and the rest (52%) are considered as a Fair (C3) one.

Modeling the hydrologic effects of watershed-scale green roof implementation in the Pacific Northwest, United States

Green roofs are among the most popular type of green infrastructure implemented in highly urbanized watersheds due to their low cost and efficient utilization of unused or under-used space. In this study, we examined the effectiveness of green roofs to attenuate stormwater runoff across a large metropolitan area in the Pacific Northwest, United States. We utilized a spatially explicit ecohydrological watershed model called Visualizing Ecosystem Land Management Assessments (VELMA) to simulate the resulting stormwater hydrology of implementing green roofs over 25%, 50%, 75%, and 100% of existing buildings within four urban watersheds in Seattle, Washington, United States. We simulated the effects of two types of green roofs: extensive green roofs, which are characterized by shallow soil profiles and short vegetative cover, and intensive green roofs, which are characterized by deeper soil profiles and can support larger vegetation. While buildings only comprise approximately 10% of the total area within each of the four watersheds, our simulations showed that 100% implementation of green roofs on these buildings can achieve approximately 10–15% and 20–25% mean annual runoff reductions for extensive and intensive green roofs, respectively, over a 28-year simulation. These results provide an upper limit for volume reductions achievable by green roofs in these urban watersheds. We also showed that stormwater runoff reductions are proportionately smaller during higher flow regimes caused by increased precipitation, likely due to the limited storage capacity of saturated green roofs. In general, green roofs can be effective at reducing stormwater runoff, and their effectiveness is limited by both their areal extent and storage capacity. Our results showed that green roof implementation can be an effective stormwater management tool in highly urban areas, and we demonstrated that our modeling approach can be used to assess the watershed-scale hydrologic impacts of the widespread adoption of green roofs across large metropolitan areas.

Soil carbon improvement under long‐term (36 years) no‐till sorghum production in a sub‐tropical environment

AbstractSoil organic matter (SOM) is considered an important indicator of soil quality, which can be impacted by crop production practices such as tillage. In this study, two long‐term tillage regimes (conventional tillage [CT] and no tillage [NT], conducted for 36 years) were compared in continuous sorghum production in a sub‐tropical environment in southeast Texas. The positive effects of long‐term NT practice were more conspicuous at the soil surface compared with the deeper soil profiles. The SOC was greater (1.5 t C ha−1 greater) in the NT system compared with the CT system. Results from an incubation study indicate that the rate of C‐min at 0–5 cm soil depth was significantly greater (164 μg of CO2–C g−1 of soil greater) in NT than that of CT, but this trend was reversed at 10–20 cm depth wherein the C‐min rates were 106 μg of CO2–C g−1 of soil greater in CT compared with NT, which is likely because of soil disturbance during the study. Soil cumulative CO2‐C emissions were greater in the CT system (7.28 g m−2) than in the NT system (5.19 g m−2), which is primarily attributed to high soil temperature conditions in the CT system. Sorghum grain yield however was not influenced by the differences in SOC content in this long‐term experiment. Overall, the present study found that long‐term conservation tillage improved SOC stock and reduced carbon loss, thus had a positive impact on soil health and sustainability.

Water use strategy of Ammopiptanthus mongolicus community in a drought year on the Mongolian Plateau

Abstract Aims In desert ecosystems, water is a restricting factor for plant growth and vegetation dynamics. The relatively stable water source from deep soil profile or groundwater is important for plant survival during drought. Understanding water use strategy of endangered species, in desert ecosystem is essential for their conservation and restoration such as Ammopiptanthus mongolicus on the Mongolian Plateau. Methods The stable isotope method of δD and δ 18O was used to examine the main water sources of A. mongolicus and two companion shrubs, e.g. Artemisia ordosica and Artemisia xerophytica. The contribution of different water sources to each species was calculated by IsoSource model. Leaf δ 13C was used to compare long-term water use efficiency of three shrubs. Soil moisture and root distribution of three shrubs was measured to explain plant water use strategy. Important Findings The results showed that A. mongolicus relied on groundwater and 150–200 cm deep soil water, with the former contributing to almost half of its total water source. Artemisia ordosica mainly used 150–200 cm deep soil water, but also used shallow soil water within 100 cm in summer and autumn. Artemisia xerophytica mainly used 150–200 cm deep soil water and groundwater, with the latter contributing to about 30%–60% of its total water source. The three shrubs had dimorphic or deep root systems, which are in accord with their water sources. The WUE in the evergreen shrub A. mongolicus was higher than in two deciduous Artemisia shrubs, which may be an adaptive advantage in desert ecosystem. Therefore, groundwater is an important water source for the endangered shrub A. mongolicus in a drought year on Mongolian Plateau. Ammopiptanthus mongolicus and two Artemisia shrubs competed for deep soil water and groundwater.

Evaluating permafrost physics in the Coupled Model Intercomparison Project 6 (CMIP6) models and their sensitivity to climate change

Abstract. Permafrost is a ubiquitous phenomenon in the Arctic. Its future evolution is likely to control changes in northern high-latitude hydrology and biogeochemistry. Here we evaluate the permafrost dynamics in the global models participating in the Coupled Model Intercomparison Project (present generation – CMIP6; previous generation – CMIP5) along with the sensitivity of permafrost to climate change. Whilst the northern high-latitude air temperatures are relatively well simulated by the climate models, they do introduce a bias into any subsequent model estimate of permafrost. Therefore evaluation metrics are defined in relation to the air temperature. This paper shows that the climate, snow and permafrost physics of the CMIP6 multi-model ensemble is very similar to that of the CMIP5 multi-model ensemble. The main differences are that a small number of models have demonstrably better snow insulation in CMIP6 than in CMIP5 and a small number have a deeper soil profile. These changes lead to a small overall improvement in the representation of the permafrost extent. There is little improvement in the simulation of maximum summer thaw depth between CMIP5 and CMIP6. We suggest that more models should include a better-resolved and deeper soil profile as a first step towards addressing this. We use the annual mean thawed volume of the top 2 m of the soil defined from the model soil profiles for the permafrost region to quantify changes in permafrost dynamics. The CMIP6 models project that the annual mean frozen volume in the top 2 m of the soil could decrease by 10 %–40 %∘C-1 of global mean surface air temperature increase.

Ammonia nitrogen sources and pollution along soil profiles in an in-situ leaching rare earth ore

The ammonium sulphate ((NH4)2SO4) in-situ leaching process is the most widely used extraction technology for weathered crust elution-deposited rare earth ores (WCED-REOs). Highly concentrated (NH4)2SO4, a representative leaching agent, is often used in the leaching process of WCED-REOs. However, this in-situ leaching process causes nitrogen pollution in the soil, surrounding surface and ground water due to the high concentrations of (NH4)2SO4 solutions used as a long term leaching agent. To date, the mechanism behind the variations in ammonia nitrogen (AN) in deep soil profiles is unclear. We conducted vertical and lateral soil sampling and analyzed the collected samples for soil moisture, pH, ammonia forms, and AN contents in soil profiles deeper than 500 cm in an in-situ leaching mining area of Ganzhou, Jiangxi Province, southern China. The results show that primary chemical pollutants in the soil are derived from residual leaching agents with high acidities and concentrations of AN. Twelve years after the mining process was completed, the mean pH values of the tailings in the mining area were 3.90 and 4.87 in its lower reaches. Due to the presence of chemical residues, the AN concentration was 12–40 times higher than that of the raw ore soil before it was mined. The percentages of different ammonium forms in the rare earth tailing soil were 65%, 30%, and 5% for the water-soluble, exchangeable, and fixed ammonium forms, respectively. The results of this study support effective prevention and remediation treatment of environmental problems caused by AN pollution of the soil in WCED-REOs.

Multifractal characteristics of particle size distributions (50–200 m) in soils in the vadose zone on the Loess Plateau, China

The soil particle size distribution (PSD) is an important and basic physical property that determines many other chemical, physical, and biological properties of soil. Thus, quantitatively characterizing the soil PSD is important. However, the PSDs have not been characterized previously in deep soil profiles on the Loess Plateau, China. Therefore, in the present study, we employed single fractal theory and multifractal theory to quantitatively characterize these PSDs. Soil samples (50–200 m) were collected from the top of the soil profile down to the bedrock by drilling at five sites on the Loess Plateau in China. The results showed that the sand content had the highest coefficient of variation (CV) whereas the silt content had the lowest CV. Single fractal dimension (D) analysis detected significant positive relationships between D and the silt and clay contents, but a significant negative relationship with the sand content. Multifractal analysis indicated that the capacity dimension (D0) values at five sites tended to increase from south to north, whereas a decreasing trend was determined for the information dimension/capacity dimension (D1/D0). Yangling had the lowest Δα and ΔD values, whereas Ansai had the highest. The Δf values were highest at Ansai and Shenmu. Our results are important to understand the soil physical properties and to estimate the soil hydraulic properties in deep profiles on the Loess Plateau.