Steppe Soils Research Articles

Distribution characteristics of soil particle size in alpine steppe and alpine meadow in the source region of the Yangtze River, China.

To explore the heterogeneity of spatial distribution and particle size distribution (PSD) in the main underlying surface soil in the source area of the Yangtze River, we used the fractal theory to describe the soil particle size distribution of alpine steppe and alpine meadow, and analyzed the difference of fractal dimension characteristics of soil of two different underlying surface and its relationship with soil particle composition. The results showed that soil particle size in the study area was mainly concentrated in 100-800 μm. The single fractal dimension (DV) of alpine steppe soil was 2.429-2.508, and that of alpine meadow soil was 2.697-2.743. The soil texture of alpine steppe was coarse, while that of alpine meadow soil was fine. Soil texture was the finest in the 20-30 cm depth, and the coarsest in the 0-10 cm layer. The multi-fractal dimension (capacity dimension D0, information entropy dimension D1, correlation dimension D2) of alpine steppe (0.896-0.961, 0.828-0.887, 0.725-0.819) was higher than that of alpine meadow (0.890-0.914, 0.693-0.744, 0.540-0.603). Compared with the alpine meadow, the alpine steppe had wider soil PSD, more complex soil structure, and higher soil heterogeneity. DV was positively correlated to clay and silt contents, and negatively correlated to sand content. D1 and D2 were negatively correlated with clay and silt contents, and positively correlated with sand content. Sand content was the main factor accounting for the non-uniform distribution of PSD and the changes of fractal dimension.

Soil microbial properties of subalpine steppe soils at different grazing intensities in the Chinese Altai Mountains

Long-term provision of ecosystem services by grasslands is threatened by increasing stocking densities. The functions of grassland ecosystems depend on a mutual relationship between aboveground and belowground biota. While the effects of increasing stocking density on plant biomass are well studied, little is known about its impact on soil microbial properties. To fill this knowledge gap a grazing experiment was conducted on a summer pasture in the Chinese Altai Mountains during the summers of 2014 and 2015 using a randomized block design with stocking densities of 0, 8, 16, and 24 sheep ha−1 replicated four times. After two summer grazing periods (each 56 days), topsoil samples (1–7 cm) were taken in September 2015 and analyzed for major physical, chemical, and microbial soil properties. Except for the metabolic quotient (qCO2; p < 0.05), the examined soil properties remained unaffected by the increasing stocking densities, likely due to high spatial variability. The qCO2 declined from 13.5 mg CO2–C g−1 microbial biomass C d−1 at zero grazing to 12.2 mg CO2–C g−1 microbial biomass C d−1 at a stocking density of 24 sheep ha−1. Low values of qCO2 indicate an aged and dormant microbial community that diverts less soil organic carbon (SOC) to catabolic processes within their cells, characteristic for C limiting conditions. The aboveground biomass affected by grazing intensity correlated positively with SOC (rs = 0.60, p = 0.015) and ergosterol (rs = 0.76, p = 0.001) pointing indirectly to the effect of stocking density. Additionally to the relatively high values of qCO2, highest values of SOC (39.2 mg g−1 soil), ergosterol (6.01 µg g−1 soil), and basal respiration (10.7 µg g−1 soil d−1) were observed at a stocking density of 8 sheep ha−1 indicating that a low grazing intensity is recommendable to avoid soil degradation.

Manifestations of Salinity and Solonetzicity in Zonal Soils of Mongolian Dry Steppes

The taxonomic position of dry-steppe (chestnut) soils mentioned in the books Classification and Diagnostics of Soils of the USSR (1977), Classification and Diagnostics of Soils of Russia (2004), and World Reference Base for Soil Resources (2014) is discussed. Based on the example of the soils of Mongolia, it is shown that the soils of dry steppes that formed on light nonsaline parent rocks are normally nonsaline and nonsolonetzic. The soils of Mongolian dry steppes that formed on saline rocks are saline and solonetzic. The soils with profiles that include loamy layers (even those with a predominantly light granulometric composition and formed on nonsaline rocks) normally feature signs of solonetzicity in the loamy horizons.

АГРОХИМИЧЕСКИЕИАГРОФИЗИЧЕСКИЕОСОБЕННОСТИКАШТАНОВЫХ ПОЧВ ЗОНЫ СУХОЙ СТЕПИ АЛТАЙСКОГО КРАЯ

The mathematical models of regional soil standards for the dry steppe zone were developed. Four soil regions were identified in the dry steppe zone in accordance with the soil-geographic zoning of the Altai Region. It is shown that the taxonomic boundaries of the agrochemical proper-ties of the soil standards may differ in different soil regions. On that ground, the regional soil classification at the level of soil regions was differentiated. Significant differences of the agrochemical properties of the Kashtanozem soil sub-types in four soil regions are shown. These differences are due to the geochemical features of their genesis and agro-genic transformations. The agrochemical properties reflect the changes associated with the long-term agricultural use of dry steppe soils: agricultural depletion of mobile nutrient АГРОНОМИЯВестник Алтайского государственного аграрного университета No 8(202), 202145content, absorbed bases and the changes of agrophysical properties -the degradation of Kashtanozems caused by deflation. This is proved by the decreased content of clay and silt fractions in the particle-size composition of the plowing soil horizon. It is proposed to use the classification boundaries of regional soil standards for monitoring their agrochemical and ecological state.

To the Question of the Study of the Ecological State of Steppe Soils

This article presents conclusions about the ecological state of steppe soils, which were obtained as a result of the EPR (Electronic paramagnetic resonance) spectroscopy method and the microbiological method. The selection of soil samples for the study was carried out in the steppes of different territories: Voronezh region; Rostov Region; Volgograd Region; Republic of Kalmykia. It was revealed that free radicals were present in all soil samples.

Spatiotemporal patterns and drivers of methane uptake across a climate transect in Inner Mongolia Steppe

Steppe soils are important biological sinks for atmospheric methane (CH4), but the strength of CH4 uptake remains uncertain due to large spatiotemporal variation and the lack of in situ measurements at regional scale. Here, we report the seasonal and spatial patterns of CH4 uptake across a 1200 km transect in arid and semi-arid steppe ecosystems in Inner Mongolia, ranging from meadow steppe in the east plain to typical and desert steppes on the west plateau. In general, seasonal patterns of CH4 uptake were site specific, with unimodal seasonal curves in meadow and typical steppes and a decreasing seasonal trend in desert steppe. Soil moisture was the dominant factor explaining the seasonal patterns of CH4 uptake, and CH4 uptake rate decreased with an increase in soil moisture. Across the transect, CH4 uptake showed a skewed unimodal spatial pattern, with the peak rate observed in the typical steppe sites and with generally higher uptake rates in the west plateau than in the east plain. Soil moisture, together with soil temperature, soil total carbon, and aboveground plant biomass, were the main drivers of the regional patterns of CH4 uptake rate. These findings are important for model development to more precisely estimate the soil CH4 sink capacity in arid and semi-arid regions.

Soil extracellular enzyme activities and the abundance of nitrogen-cycling functional genes responded more to N addition than P addition in an Inner Mongolian meadow steppe

Nitrogen (N) and phosphorus (P) availability in soils commonly limit belowground biological processes in terrestrial ecosystems. Soil extracellular enzyme activities (EEAs) and microbial functional groups play critical roles in soil biological processes and nutrient cycling, yet their response to nutrient addition are poorly understood. To address this issue, we applied six fertilization treatments composed of combinations of N (0, 1.55, 13.95 g N m−2 yr−1) and P (0, 5.24 g P m−2 yr−1) for two years in a meadow steppe of Inner Mongolia. Soils were collected from each plot in July and August and analyzed for abundances of N-cycling genes and EEAs, and their relationships with treatments. The addition of N significantly increased C-acquisition enzyme activity and enzyme C:N and C:P ratios. Enzymatic stoichiometry indicated that N addition alleviated microbial demand for N, while it increased microbial C limitation. Microbial C and N limitation were significantly correlated with NH4+–N in July, yet they were correlated with soil water content (SWC) in August. The abundance of amoA significantly increased with N addition and was positively related to mineral-N accumulation. The abundance of denitrifier genes and gaseous N loss potential were accelerated by N addition in July, while a neutral effect was observed in August. Nitrate leaching potential was significantly increased by N addition, yet it declined with P addition in July. P addition also suppressed amoA abundance of ammonia oxidizing bacteria. Partial least squares path modelling indicated that N addition positively affected microbial-C limitation, soil N-loss potential and negatively affected microbial-N limitation. P addition negatively affected soil N-loss potential. Ultimately, this study highlights the importance of soil N availability in regulating microbial metabolism and soil N-loss potential, and enhances our understanding of the mechanisms responsible for variation in microbial nutrient cycling in meadow steppe soils.

Розподіл голих амеб у ґрунтах степової зони України

As a result of the study, in the steppe zone of Ukraine (Odessa, Mykolaiv, Kirovohrad region), 12 species of naked amoebas were identified, which according to the modern Eukaryot system belong to three molecular clusters Tubulinea Smirnov et al., 2005, Discosea Cavalier-Smith, 2004., Discoba Simpson and Hampl et al., 2009. This species Vahlkampfia sp. (1), Vahlkampfia sp. (2), Deuteramoeba mycophaga Page, 1988, Saccamoeba stagnicola Page, 1974, Vexillifera sp., Vannella sp. Ripellaplatypodia Smirnov, Nassonova, Chao et Cavalier-Smith, 2007, Cochliopodium sp. (1), Mayorella sp., Thecamoeba striata Penard, 1890, Stenamoeba stenopodia (Page, 1969) Smirnov et al., 2007, Acanthamoeba sp. (1). In the studied steppe soils, the most common were Vahlkampfia sp. (2), S. stenopodia, Vahlkampfia sp. (1), Vexillifera sp., Cochliopodium sp. (1); the least common – R. platypodia, D. mycophaga, T. striata, Mayorella sp. As a result of the cluster analysis, it was found that the largest share of common species is observed between Mykolaiv and Kirovograd regions (0.71) and Odessa and Kirovograd regions (0.53); the smallest is between the Odessa and Mykolaiv regions (0.43). According to the results of cluster analysis, the faunistic complexes of soil species of amoebae of the steppe region of Ukraine are united into two clusters: one of them being complexes characteristic of the Odessa region, and the other complexes of the Mykolaiv and Kirovograd regions. According to the results of nonparametric multidimensional scaling, it is established that the species complex of soil amoebae in the Kirovograd and Mykolaiv regions is determined by the increased soil temperature and acidity, compared to the Odessa region. As for moisture, this factor has little effect on the species complexes amoebae steppe region of Ukraine.

Оцінка екологічної ефективності схеми формування агроландшафтів на рівні: система балкових водозборів → балкові водозбори р. Айдар

Goal. To assess ecological efficiency of the scheme of formation of agrolandscapes at the level: system of gullen drainage areas → gullen drainage areas of the Aidar river. Methods. Laboratory-field, mathematical-statistical, topometric, morphological. Results. The basic erosion-ecological situation of the object of research is determined. PS levels are calculated for the Steppe zone. An Integral map of soil erosion hazard classes of the Steppes of Ukraine is constructed. At the level of the system of gullen drainage areas of the Aidar River, the analysis is carried out of the nature of the impact of forecast and actual erosion-hydrological indicators (runoff costs) on the development of erosion-hydrological processes on a probabilistic basis (1; 5; 10; 50%) by their ratio. On the example of the Yevsuh and Kovsuh river basins, plowing indicators are calculated for key drainage areas along the river with differentiation of administrative land use. The map of the structure of the Yevsug and Kovsug river basins within the drainage areas is constructed. The structure of sown areas and their plowing is assessed according to the potential runoff indicator: up to 5 mm — insignificant, 5.1–8 — weak, 8.1–15 mm — moderate, with erosion index levels (3 and lower; 3–4; 4–5; 5 and above) and grouping the structure of sown areas. According to the simplex method, the analysis of actual and forecast erosion-hydrological indicators and optimization of the structure of sown areas is carried out. For the Aidar River basin the model structure of crop rotations is obtained. Ecological assessment of the structure of crop rotations is performed according to the coefficient of ecological danger of crop rotations. Conclusions. At the level of the gullen drainage areas system, the coefficient of the ratio of KV of forecast and actual losses of the river runoff as an indicator of the development of erosion-hydrological processes on a probabilistic basis (1; 5; 10; 50%) at hydro-posts along the Aidar River showed that at 10% security in case of reduction of plowed lands to 50–60%, a high level of runoff reduction (81–90%) was observed at the Bakhmutivka hydro-post, medium (73–85%) — at Bilolutsk and Starobilsk hydro-posts, the lowest — at the Kuriachivka hydro-post (39–65%). The study of humus content in the range of 4.5–5.5% by groups of arable land areas 40–60% revealed constant decrease in Qmax (average maximum runoff losses) in the range of 8–9%. At the level of individual gullen drainage areas, the determination of the basic erosion-ecological situation of the object of research on the integrated map of erosion hazard classes of steppe soils of Ukraine showed its belonging to the class of moderate erosion hazard with runoff of 8.1–15.0 mm.

Distribution Characteristics of Soil Organic Phosphorus Fractions in the Inner Mongolia Steppe

Phosphorus (P) is one of the limiting nutrients in Inner Mongolia steppe soil, which seriously affect steppe productivity. Therefore, it is necessary to understand the distribution characteristics of organic P (Po) fractions and their influencing factors in Inner Mongolia steppe soil and to identify the contribution of Po fractions to soil available P (AP) to maintain the sustainable development of the Inner Mongolia steppe by improving the utilization rate of Po. The contents of soil Po fractions such as H2O-extractable Po (H2O-Po), NaHCO3-extractable Po (NaHCO3-Po), HCl-extractable Po (HCl-Po), NaOH-extractable Po (NaOH-Po), and phytate P (Phyt-P) were determined in soil samples (0–15 cm) from 15 sampling sites representing three types of grassland (i.e., desert steppe, typical steppe, and meadow steppe) in Inner Mongolia. The influencing factors of the soil Po fractions were determined by redundancy analysis (RDA). Soil Po content accounted for 61.0% of the total P (TP) on average. NaOH-Po was the main fraction of Po, accounting for 49.1% of Po on average; H2O-Po content accounted for the least amount of Po (mean 1.3 mg kg−1). H2O-Po and HCl-Po were not significantly different among the three steppes. The contents of NaHCO3-Po increased in the order of desert steppe < typical steppe < meadow steppe, and the trend of NaOH-Po and Phyt-P contents were desert steppe < meadow steppe < typical steppe. Pearson correlation analysis showed that NaHCO3-Po was positively correlated with AP (r = 0.86, p < 0.01). HCl-Po was negatively correlated with AP (r = − 0.56, p < 0.05). NaOH-Po and Phyt-P were significantly positively correlated with NaHCO3-extractable inorganic P (NaHCO3-Pi); Phyt-P was also negatively correlated with HCl-extractable Pi (HCl-Pi) (r = − 0.61, p < 0.05). These correlations were mainly caused by differences in steppe types and soil properties caused by climatic conditions, as shown by the result of RDA analysis. Soil Po plays an indispensable role in the supply of soil P in the semi-arid steppe of Inner Mongolia, where NaHCO3-Po and HCl-Po strongly contributed to AP. In addition, NaOH-Po and Phyt-P as a part of stable pools are important for providing P to other P pools. Po fractions in steppe soils were mainly regulated by climatic conditions and are closely related to the soil organic matter and pH.

Effect of increasing precipitation and warming on microbial community in Tibetan alpine steppe

Soil microorganisms play an important role in regulating the feedback of Alpine steppe ecosystems to future climate change. However, the interaction effect of warming and increasing precipitation on soil microorganisms remains unclear, in the face of an ongoing warmer and wetter climate on the Tibetan Plateau. In this study, we investigate the multi-factorial effects on soil microbial diversity, community structure, and microbial interactions in a three-year climate change experiment established in an Alpine steppe on the Tibetan Plateau, involving warming (+2 °C), +15% increasing precipitation and +30% increasing precipitation. Compared to warming, warming plus increasing precipitation alleviated the decrease in microbial diversity, and increased the dissimilarities in microbial community structures, largely influenced by water and substrate availability. We further observed differences in moisture increased the differences in microbial diversity and dissimilarities in microbial community structures across different precipitation levels under ambient temperature. Interestingly, warming plus increasing precipitation could create more ecological niches for microbial species to coexist but may lessen the strength of microbial interactions in contrast to increasing precipitation alone. Collectively, our findings indicate that microbial responses to future climate change in Alpine steppe soils will be more complex than those under single-climate-factor conditions.

Actualization of the contents of the soil map of Russian Federation (1 : 2.5 M scale) in the format of the classification system of Russian soils for the development of the new digital map of Russia

The Soil Map of the Russian Federation, 1 : 2.5 M scale (1988) requires updating to include soil data that have been accumulated in the past decades, reflect real changes in the soil cover, including anthropogenic transformation, and ensure precise localization of soil objects and correspondence of the map to satellite data with the use of digital soil mapping technologies. The substantive-genetic classification system of Russian soils (2004, 2008) provides the conceptual basis for this updating. The conversion of soil information from the initial map of 1988 into the new classification system is being performed for each polygon of the digitized map. It is based on the analysis of a vast body of diverse information and includes both the search for analogues of the names of mapping units in the new classification system (renaming of the soils) and the correction of the composition of soils in the polygons: new natural soils, cultivated soils (agrosoils), and urban soils are added to the attribute database. The largest number of new natural soils has appeared in legend sections “Soils of tundra” and “Soils of taiga and broadleaved forests”. Anthropogenic soils (119 legend units) that are shown on the map for the first time, have their maximum representation (36 units) in the section “Soils of steppes”; it is close to the number of natural soils (37 units) in this zone. A considerable percent of anthropogenic soils (&gt; 50% of the natural soils) is also typical of legend sections “Soils of broadleaved forests and forest-steppes,” “Soils of dry steppes and semideserts,” “Salt-affected and solonetzic soils”. The total number of natural and anthropogenic soil units (425) in the new legend is more than twice as large as the initial number of natural soil units in the base map (205). The results of the renaming and updating of soils for each soil polygon are fixed in a separate section of the attribute database to the map and will be used for generating the new map by the methods of digital soil mapping.

Chemical Soil-Biological Engineering Theoretical Foundations, Technical Means, and Technology for Safe Intrasoil Waste Recycling and Long-Term Higher Soil Productivity

The amelioration and remediation technology was developed on the basis of research of phosphogypsum and utilization in the Haplic Chernozem of South-European facies (Rostov Region). Phosphogypsum was utilized via dispersed application into a soil layer of 20–45 cm with intrasoil milling of this layer. The phosphogypsum utilization doses were 0, 10, 20, and 40 t ha–1. The Pb analytical content in soil solution was studied in the model experiment. The soil solution Pb thermodynamic forms were calculated. The mathematical chemical–thermodynamic model ION-2 was developed to calculate the real soil solution (water extract) calcium-carbonate equilibrium (CCE) ion forms, considering the ion pair association. The associated ion pairs CaCO30, CaSO40, MgCO30, MgSO40, CaHCO3+, MgHCO3+, NaCO3–, NaSO4–, CaOH+, and MgOH+ were accounted for in soil solution equilibrium macroion form calculation. The procedure for the microelement ion [including heavy metals (HMs)] equilibrium concentration in the soil solution coefficient kas calculation was proposed to account for the real soil solution CCE, macroions, and HM (including Pb) association. The Pb2+ ion in soil solution was mostly bound to associates PbOH+, Pb(OH)20, PbCO30, Pb(CO3)22–, and PbHCO3+. The calculation of CCE and ion association in soil solution revealed 14.5–21.5 times HM passivation compared to HM water-soluble values. The calculated HM activity in the soil solution in the example of the Pb2+ ion was less than 4% after phosphogypsum application in the target amelioration layer of 20–45 cm. The studied phosphogypsum doses were substantiated as environmentally safe. This was because the real soil solution CCE provided HM ion form association and consequent passivation. The dry steppe soil remediation after phosphogypsum application was justified as highly probable. The intrasoil milling chemical soil-biological engineering technology was developed for simultaneous soil amelioration and remediation on the basis of the biogeosystem technique (BGT*) transcendental methodology. The BGT*-based technology was tested in the long-term field experiments and is capable of ensuring the priority geophysical micro- and macroaggregate structure via intrasoil milling and mixing of soil illuvial and transitional horizons. This helps synthesize soil multilevel architecture, providing intrasoil-dispersed environmentally safe recycling of wastes of different origin. Addressing the environment safety concerns, a new decision of the intrasoil milling device was proposed for phosphogypsum and other substance application to soil.

Characteristics and sources of heavy metal pollution in desert steppe soil related to transportation and industrial activities.

A study area was selected from the industrial region of Gaoshawo Town, Yanchi County, Ningxia, to explore the level of heavy metal pollution in desert grasslands due to industrial activities. A total of 82 surface soils were collected, and the concentration of heavy metals, namely, Cu, Cd, Cr, Pb, Zn, Mn, and Co, was determined by ICP-AES (atomic emission spectrometer) (HK-8100); the average values were 21.64 ± 3.26, 0.18 ± 0.02, 44.99 ± 21.23, 87.18 ± 25.84, 86.63 ± 24.98, 570.49 ± 171.57, and 17.96 ± 9.96mgkg-1. The single-factor, Nemerow pollution, and potential ecological risk index methods were used to evaluate the status of soil heavy metal pollution and the contribution from the major sources identified by the receptor model. The results showed that 9.09% of the samples were slightly polluted, 32.47% of the samples were moderately polluted, and 58.41% of the samples were heavily polluted. The comprehensive potential ecological risk index indicated that 90.79% of the samples had moderate ecological risk. It was verified from the models and spatial distribution maps that Cr, Co, Zn, and Mn are mainly contributed by the industrial sources that account for 55.04%, 92.13%, 50.05%, and 48.77% of these heavy metals, respectively. The heavily contaminated areas are distributed around the industrial park. A total of 70.63% and 77.83% of Cu and Pb are contributed by transportation sources, respectively, with the concentrations decreasing from southwest to northeast. The contribution from agricultural activities to Cd is 77.02%, with concentrations largely distributed in the north of the highway. This study showed that the existence of the Gaoshawo Industrial Zone and the corresponding industrial and transportation activities have a significant impact on the grassland soil environment.

Postagrogenic Changes in the Enzyme Activity and Organic Carbon Content in Chernozem during the First Three Years of Fallow Regime

Comprehensive studies of the biological status of ordinary chernozem (Haplic Chernozem (Loamic)) were carried out in the early years of the fallow regime in comparison with its arable analogue, old fallow, and the reference virgin steppe soils. They included a field experiment on the conversion of an old-arable plot with the ordinary chernozem in Botanical Garden of the Southern Federal University to a fallow. In this experiment, organic carbon and the activity of two classes of enzymes, oxidoreductases (catalases and dehydrogenases) and hydrolases (β-fructofuranosidase) were compared for soils under land-use variants. The organic carbon content in the soil of the young fallow increased already in the first year; it did not change significantly in subsequent years of plant cover restoration, and varied depending on the observation period during the growing season. The activity of the enzymes also increased in the first year of the fallow regime and continued to restore throughout the time after the cessation of agricultural use. The catalase activity in the young fallow soil was 9% higher (p < 0.05) than in the first year of research, the activity of dehydrogenases increased by 20% (p < 0.05), and β-fructofuranosidase by 10% (p < 0.05). However, the enzymatic activity was significantly lower than in the case of old fallow and, especially, of the reference soil in the virgin steppe.

Plantations d’&lt;em&gt; Atriplex canescens &lt;/em&gt; en vue de la restauration des parcours dégradés en steppe algérienne

La steppe algérienne est le milieu d’élevage du mouton par l’exploitation de ses parcours. Dans sa partie aride, la vulnérabilité du milieu est aggravée par une exploitation principalement pastorale de plus en plus intense durant ces dernières décennies. Cette tendance régressive est caractérisée par une baisse dela productivité fourragère et les espèces pérennes sont les plus touchées. L’Etat algérien a mis en oeuvre un programme d’aménagement des espaces steppiques très dégradés à travers la plantation d’espèces végétales résistantes et productives de biomasse comme Atriplex spp. L’objectif de ce travail a été d’estimerla productivité pastorale de quelques stations réhabilitées par la plantation d’Atriplex canescens, comparativement aux parcours naturels pâturés. Les résultats ont montré une amélioration du recouvrement végétal (de 49 % à 60 %) et de meilleures valeurs pastorales (phytomasse, productivité, valeur énergétique et charge pastorale). Sur les zones réhabilitées une productivité énergétique et protéique de 604 unités fourragères lait / ha/an et 29 kg de matière sèche / ha/an, et une charge pastorale de 1,51 unité ovine / ha/an ont été enregistrées, alors que sur les parcours naturels dégradés ces valeurs ont été respectivement de 14 UFL, 0,422 kg MS/ha/an, et 0,03 unité ovine / ha/an. Les stations naturelles sont surexploitées et tendent vers un état de dégradation sévère de la végétation et des sols steppiques. A moins de restaurer ou de réhabiliter les parcours steppiques, leur capacité de productivité pastorale sera fortement réduite.

Soil phosphorus accumulation changes with decreasing temperature along a 2300 m altitude gradient

Understanding the abundance of organic P in soil is a prerequisite for predicting the effects of climate change on P dynamics and availability in cold alpine regions. We sampled plant roots (up to 40 cm depth) and soils (100 cm depth) in grasslands along a 2300 m altitude gradient (1286–3589 m above sea level, mean annual temperature (MAT) from 9 to 0.3 °C) between alpine steppes on the Loess Plateau and alpine meadows on the Tibetan Plateau. A modified Hedley P fractionation in combination with root and microbial P, alongside phosphatase activity, was used to characterize P transformations depending on climate. Both the roots and microorganisms stored more P and produced higher phosphatase activity in cold meadow than in warm steppe soils. Total inorganic P (Pi) content decreased in cold meadow (MAT < 3 °C) compared with warm steppe soils because of the decrease of moderately labile Pi (extracted with diluted HCl) in cold meadow soils. Available P (NaHCO3) and labile Pi (NaOH) contents increased upslope, whereas the recalcitrant Pi (concentrated HCl) contents remained stable at all sites down to 100 cm soil depth. Labile (NaHCO3), moderately labile (NaOH) and recalcitrant (concentrated HCl) organic P (Po) contents sharply increased in cold meadow compared with warm steppe soils. The residue P in the 0–100 cm along the temperature gradient was similar to that of all Po fractions. The Po proportion in the total P was less than 10 % at sites with a MAT above 3 °C, but sharply increased up to 50 % at sites with a MAT below 0.7 °C. The greater root and microbial P uptake versus slower Po mineralization in cold meadows than in warm steppes increase the incorporation of Pi into organic pools in cold alpine areas. This accumulation of Po forms is a mechanism to prevent P losses by leaching as inorganic forms. The increased plant available P in cold meadows was associated with the increased phosphatase activity and Po contents compared with warm steppe soils. We conclude that the on-going climate warming could stimulate P cycling more in cold meadows than in warm steppe regions because Po dominated the total soil P in cold areas.

Opposite responses of global warming potential to ammonium and nitrate addition in an alpine steppe soil from Northern Tibet

Deposit of inorganic nitrogen (N) in different forms may divergently impact soil greenhouse gas (GHG) emissions and then aroused different feedback of global warming potential (GWP). Nevertheless, little information is available in alpine grassland ecosystems, it is far from elucidated. In this study, the effects of ammonium (NH4+-N) and nitrate (NO3−-N) addition on GHG emissions were evaluated by using laboratory incubation for an alpine steppe soil in northern Tibet. Six-level N gradient was set for the incubation: 14 (2T), 28 (4T), 56 (8T), 112 (16T), 224 (32T), 448 (64T) kg·ha−1·year−1. Our results showed that NH4+-N and NO3−-N addition significantly increased and decreased soil CO2, respectively. In general, NH4+-N addition had a stronger promotion to N2O emission and a stronger inhibition to CH4 uptake compared with NO3−-N addition at same level. Besides, GHG emissions increased or decreased linearly with inorganic N addition gradient (P < 0.05), and sharp N2O emissions were observed when NH4+-N input amounts more than 400 kg ha−1·year−1 (64T). On the whole, there was an opposite responses of global warming potential (GWP) to NH4+-N and NO3−-N addition, in which NH4+-N addition increased, but NO3−-N addition decreased. The GWP was mainly contributed by CO2 emission (>84%) in alpine steppe soil from Northern Tibet. The results suggested that NO3−-N input likely to be more eco-friendly than NH4+-N input in alpine steppe area, it may have implications in environmental policy related to the anthropogenic emissions of the two N forms.

The contact angle of wetting as an integral indicator of physical-chemical properties of Сhernozems of Kamennaya Steppe

The sessile drop method was used to measure the contact angle of wetting (CA) of ordinary Chernozem from the fields of the Kamennaya Steppe agrolandscape used in various ways. The treatments differ in the intensity of tillage operations (protected mowed steppe, arable land after moldboard plowing), the use of mineral fertilizers and their aftereffect, as well as changes in soil properties under the influence of irrigation. At the same time, the total organic carbon content, C/N ratio, specific surface area, and rheological parameters were determined for the physical and chemical characteristics of soils. The results of the study showed that the hydrophilic-hydrophobic properties of the surface of the solid phase of soils, which largely determine the main structure-forming properties of soils, can be characterized by the value of the wetting edge angle. The CA of the studied soil samples varies from 32 degrees (highest wettability) to 45 degrees (lowest wettability). The lowest wettability is due to the increased content of hydrophobic compounds in the organic matter of soils and is characterized by the highest CA and is typical for native, untreated soil of the mowed steppe, which differs from other studied variants of the experiment in all explored physical and chemical parameters. Moldboard plowing as well as fallowing lead to changes in the physical and chemical properties of the soil and the qualitative composition of organic matter in the direction of their deterioration and a decrease in the CA. The use of mineral fertilizers contributes to the increase in the studied indicator mainly due to changes in plant productivity, in particular, the differences in CA are due to the impact of root secretions and plant residues on the soil properties. For the studied soils, the CA changes in the following series: mowed steppe &gt; arable land with the mineral fertilizers application &gt; arable land undergone the aftereffect of fertilizers. Correlation analysis revealed the relationship of CA with organic carbon content, specific surface area, and rheological characteristics of Chernozems. Thus, CA can serve as an integral indicator of changes in the physical and chemical properties of soils, their degradation changes under the conditions of different agricultural load. The method used in this research for determining CA requires a smaller amount of sample compared to rheological methods and is generally more informative than determining the content of organic matter.

Applicability of X-ray fluorescence spectrometry for assessing geochemical features and heavy metal contamination of soils: primary data

ABSTRACT X-ray fluorescence spectrometry (XRF) has long been considered a convenient and powerful method for the determination of trace amounts of chemical elements in various types of natural materials. XRF is rapid, reliable, and non-destructive spectroscopic technique, allows performing a direct analysis of solid samples without pretreatment. For the present report, we take advantage of the multielemental capability of the XRF-technique for the determination of major and trace amounts of rock-forming (Stot, Na2O, MgO, Al2O3, SiO2, P2O5, K2O, CaO, TiO2, MnO, Fe2O3(tot)) and trace (F, V, Cr, Co, Ni, Cu, Zn, Ga, Pb, Rb, Sr, Y, Zr, Nb, Ba, La, Ce, Nd) elements in environmental solid samples. Nowadays, study of the soil cover exposed by human-caused impact is an important aspect in understanding the geochemical processes occurring in it. Study object is the biggest territory of the Baikal region named Olkhon, which is a natural area of preferential protection of federal significance and a part of the Baikal National Park. In this study, we have determined chemical composition of the soil upper horizon (~0–15 cm) of meadow-stepper landscapes of the Baikal region (the Olkhon Island) to reveal their geochemical features and heavy metal pollution level. Three varieties of the steppe soils were distinguished: middle loamy, light loamy and sandy loam. For the first time, the influence of soil granulometric features on the content level of the rock-forming and toxic elements in them has been established. In addition, the primary data relating to the assessment of the soil heavy metal contamination have been presented.