M. Soleimanzadeh; F. Khormali; M. Sohrabi; R. Ghorbani Nasrabadi; M. Kehl
Abstract
Introduction Biological soil crusts are a widespread community of cyanobacteria, green alga, lichens, mosses, and other organisms. These crusts play important roles in arid and semi-arid ecosystems, such as carbon and nitrogen fixation, soil protection against water and wind erosion, and water retention. ...
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Introduction Biological soil crusts are a widespread community of cyanobacteria, green alga, lichens, mosses, and other organisms. These crusts play important roles in arid and semi-arid ecosystems, such as carbon and nitrogen fixation, soil protection against water and wind erosion, and water retention. In arid and semi-arid regions, the biological soil crusts also possess a key role in the global carbon cycle due to the carbon fixation (photosynthesis) and its release (respiration) into the atmosphere. These organisms increase the organic carbon content of the soil in arid and semi-arid regions by performing photosynthesis. Soil organic carbon is a mixture of various components and one of the important characteristics for soil quality evaluation. Biological attributes of soil quality include many soil components and processes related to the organic material cycle, such as total organic carbon and nitrogen, microbial biomass, carbon and nitrogen mineralization, labile fractions of elements, the activity of enzymes, and animals and plants in soil. These biological attributes respond rapidly to natural and human-derived changes, and therefore they are used as indices for quality of soils. Biological soil crusts are the main cover of the loess soil surface in the northern parts of Golestan Province. The region that was selected to be studied in the province was Maraveh Tappeh. This region has arid and semi-arid climate and is attributed to low vegetation, especially on the slopes to the south. In these slopes, biological and physical crusts are dominant. Therefore, a study was conducted to investigate the effect of lichen biological soil crusts on organic carbon and different fractions of labile carbon. Materials and Methods After extensive field studies, two species of lichen biological soil crusts were collected and transferred to the laboratory for identification. The results elucidated that the studied species were Diploschistes Diacapsis (Ach.) Lumbsch, and Fulgensia Fulgens (Sw.) Elenk, based on taxonomical identification. Soil sampling was done from 0-2 and 2-5cm depths under lichen biological and physical crusts. Soil samples were transferred to the laboratory, and then the organic carbon, carbohydrate, permanganate oxidizable carbon, microbial biomass carbon, cold-water extractable organic carbon, and hot-water extractable organic carbon were measured by standard methods. Results and Discussion Results show that lichen biological soil crusts led to the increase in soil organic carbon and different fractions of labile organic carbon related to the physical crust. As a result, the highest values for these traits were observed in soils affected by lichen biological soil crusts. Soil covered by the Diploschistes Diacapsis species had the highest amount of soil organic carbon and different fractions of labile organic carbon in comparison to the Fulgensia Fulgens species in 0-2cm depth, which had a significant difference at 5% probability level. the physical crusts had the least amount of soil organic carbon and different fractions of labile organic carbon related to the lichen biological soil crusts, which was caused by the loss of topsoil and the lack of biological coverage. There was a positive correlation between the measured traits. There was a high correlation between hot water-extractable carbon and carbohydrate. There were high correlation coefficients between organic carbon with microbial biomass carbon, hot water-extractable carbon, and carbohydrate. In general, there was a high correlation coefficient between hot water-extractable carbon with organic carbon and other labile fractions of organic carbon except for cold water-extractable carbon, whereas there was low correlation coefficient between hot water-extractable carbon with organic carbon and other labile fractions of organic carbon. Conclusion According to the results attained from the following study, the presence of biological soil crusts on loessial soils led to the increase in organic carbon, carbohydrate, permanganate oxidizable carbon, microbial biomass carbon, cold-water extractable organic carbon, and hot-water extractable organic carbon. Diploschistes Diacapsis Species have the highest impact on organic carbon and different fractions of labile organic carbon. The High correlations show that the best attributes to evaluate the quality of soil organic carbon in the studied area are microbial biomass carbon, carbohydrate, and hot water-extractable carbon and these may be used as a good indicator to evaluate soil quality. The studied area falls within the arid and semi-arid climate, and given the erosion-prone nature of loess deposits, improper management may lead to severe problems, such as erosion and dust production. Hence, protecting lichen biological loess crusts against human activity and livestock grazing may result in lower water and wind erosion, and increase soil quality in this region.
Micromorphology and Clay mineralogy
Masoumeh Pourmasoumi Parashkouh; Farhad Khormali; Shams Ollah Ayoubi; Farshad Kiani; Martin Kehl; Eva Lehndorff
Abstract
Introduction The loess-paleosol sequences in Northern Iran are important archives that represent several cycles of Quaternary climate change and can be used to complete the information gap on loess between Europe and central Asia. Last interglacial soils derived from loess in northern Iran is represented ...
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Introduction The loess-paleosol sequences in Northern Iran are important archives that represent several cycles of Quaternary climate change and can be used to complete the information gap on loess between Europe and central Asia. Last interglacial soils derived from loess in northern Iran is represented by strongly developed Bt horizons of forest soils. In Golestan and Mazandaran area, soils under the forest are mainly classified as Alfisols or Luvisols. Interestingly, E horizons are generally not found in these soils. In the Caspian Lowlands, a pronounced precipitation gradient is reflected in mean annual precipitation rates decreasing from about 1850 mm at Bandar Anzali in the west to about 435 mm at Gonbad- e Kavoos in the east. The results of the loess climosequence in Northern Iran showed that with increasing precipitation, soil pH and calcium carbonate contents decrease, whereas soil organic carbon, clay content, and cation exchange capacity increase. For years, many efforts to quantify the soil properties led to the provision of indices of soil development. Among these indices are forms and ratios of iron, morphological, and micromorphological indices. Many studies have been carried out on the loess-paleosol sequences and modern loess soils in Northern Iran with focus on micromorphology, mineralogy, and dating but more investigation is needed with an emphasis on the forest soils with well-pronounced clay illuviation as a proxy for paleo-moisture. For this purpose, we used micromorphology and soil color indices to report the effects of precipitation gradient on the variability in the formation of soils under forest vegetation. Materials and Methods The study area is located at the northern slopes of Alborz Mountain Ranges, covered with Caspian or Hyrcanian deciduous forests. Field sampling started in summer 2015. More than ten soil pedons with loess parent material were investigated based on former studies. Finally, six representative modern pedons were selected and dug in an east-west direction on loess deposits. The climate data shows that precipitation varies from 500 mm in Qapan (Pedon 1) to up to 800 mm in Neka. Physiochemical properties of soils were studied using standard methods. Thin section prepared for soil micromorphological studies were studied and interpreted based on Bullock et al. and Stoops guideline using a polarizing microscope. The micromorphological index of soil development (MISECA), suggested by Khormali et al (2003), was calculated. Also, color indices were calculated based on Hurst (1977), Torrent (1983), and Alexander (1985) by using the Munsell color chart. In all color indices, Munsell color hue converts to a single number. Results and Discussion The results showed that the downward decalcification and the subsequent clay illuviation were the main criteria influencing the assessment of soil development in this study. So, all of the soils host argillic and calcic horizons and are classified as Alfisols and Mollisols. Micromorphological studies confirmed the morphology studies in the field and the results of physico-chemical analyses. MISECA index showed pedological changes in different pedons in the studied areas. A significant positive relationship between climate gradient (increasing rainfall) and MISECA index was found. The area and thickness of clay coatings show an increasing trend with rainfall. Occurrence and preservation of clay coatings are more pronounced in more humid regions with illite and vermiculite as the dominant clay minerals. These minerals reduce the shrink/swell potential and increase the number of clay coatings present. In Argillic horizons of all pedons, except Toshan, dominant b-fabric is speckled due to carbonate leaching, while in Toshan, it is striated b-fabric. In calcite horizon, b-fabric is crystallitic. The correlation of various forms of iron with three color indices of Hurst, Torrent, and Alexander showed that Torrent and Alexander indices were better than the other one for the study area. Moreover, there was a good correlation between MISECA and Torrent color index. Conclusion The results showed that the soil evolution in the studied areas is strongly influenced by soil formation factors, especially in a climate which shows a change in the micromorphological characteristics of soils. With increasing the rainfall from the east to the west in this gradient, the amount and thickness of clay coating, as well as secondary calcium carbonate accumulation, change significantly. In addition, the micromorphological and color indices of soil evolution can be used as two indicators for assessing the effects of rainfall gradient on soil formation in northern Iran. On the other hand, knowledge of the development of modern loess-derived soils could help to better understand the paleoenvironment.