Soil science
Y. Kooch; A. Shahpiri; K. Haghverdi
Abstract
Introduction
Forests, encompassing approximately 30% of the Earth's land area, hold significant ecological importance due to their rich biodiversity and the multitude of environmental services they provide. These ecosystems outperform other terrestrial habitats, making them invaluable to all life forms ...
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Introduction
Forests, encompassing approximately 30% of the Earth's land area, hold significant ecological importance due to their rich biodiversity and the multitude of environmental services they provide. These ecosystems outperform other terrestrial habitats, making them invaluable to all life forms on our planet. The destruction of forest habitats and changes in land use patterns exert significant impacts on the variability of soil quality indicators. The consequence of forest degradation encompass various adverse consequences, including the destruction of wildlife habitats, climate change, global warming, diminishing plant and animal biodiversity, and reduced water conservation capacity. Extensive research has been conducted to investigate soil quality in diverse land uses within temperate regions. However, there is a noticeable scarcity of studies focusing on semi-arid regions. It is imperative to note that a comprehensive and practical assessment of soil condition necessitates the simultaneous measurement of physical, chemical, and biological indicators. Such an integrated approach ensures a thorough and effective evaluation of soil quality. The primary objective of this study was to assess the impact of various land uses, namely natural forest (C. betulus - P. persica), plantation (Q. castaneifolia), garden, rangeland, and agricultural lands (rice), on the physical, chemical, and biological properties of the organic and mineral soil layers. Specifically, the investigation focused on the evaluation of fauna and flora, microbial communities, and enzyme activities. The study was conducted in the semi-arid region of Kajur Nowshahrmourd.
Materials and Methods
To achieve this objective, contiguous sections of the study area were carefully chosen, ensuring minimal variations in height above sea level, percentage and direction of slope. Subsequently, three slice of one-hectare dimension plots (100 × 100) were selected within each study habitat, with a minimum distance of 600 meters between them. From each one-hectare plot, four leaf litter samples and four soil samples (30 cm × 30 cm, 10 cm depth) were collected and transported to the laboratory for analysis. In total, 12 litter samples and 12 soil samples were collected from each of the habitats. The soil samples were divided into two parts: one part was air-dried and then passed through a 2 mm sieve for subsequent physical and chemical testing, while the other part was stored at 4 degrees Celsius for biological assessments. One-way analysis of variance tests were employed to compare the characteristics of the organic layer and soil among the studied habitats. Furthermore, Duncan's test (P>0.05) was utilized to compare the average parameters that exhibited significant differences among the different habitats.
Results and Discussion
The findings derived from this investigation underscore the substantial variability in organic layer characteristics across different vegetation types. Natural forests emerged as the most prominent in terms of thickness, nitrogen content, and calcium concentration, whereas agricultural areas exhibited the lowest values. Grassland areas displayed the highest carbon content and carbon-to-nitrogen ratio, while agricultural and natural forest areas demonstrated comparatively lower values. Agricultural lands demonstrated elevated bulk density and sand content, whereas natural forests exhibited the lowest values. Notably, natural forests showcased the highest porosity, aggregate stability, silt percentage, and macro- and micro-aggregate quantities, while agricultural areas presented the lowest values. Chemical analysis of the soil indicated that natural forests recorded the highest values for most chemical characteristics, while agricultural lands displayed the lowest values. Biological attributes generally exhibited the highest levels in natural forests and the lowest levels in agricultural areas. Specifically, the abundance and biomass of epigeic and endogeic fauna did not exhibit significant differences among different land uses during the summer season. Managed forests demonstrated the highest values for moisture content, basal respiration, substrate-induced respiration, and microbial biomass carbon. Conversely, agriculture exhibited the lowest values in these regards. The microbial biomass carbon-to-nitrogen ratio was highest in agricultural areas, while natural forests displayed the lowest value. Natural forests displayed the highest values for most nitrogen transformation characteristics, whereas agricultural areas exhibited the lowest values. Nitrogen nitrification and mineralization showed a decreasing trend across different land uses during the summer and autumn seasons. The type of vegetation cover also significantly influenced the variability of soil ammonium and nitrate levels.
Conclusion
Based on the results obtained from this study, it can be inferred that the preservation and conservation of natural forest cover should be given utmost importance. Additionally, in degraded areas, the establishment of woody vegetation can serve as a viable approach for the restoration of ecosystems with similar ecological conditions. Furthermore, the presence of tree covers, specifically C. betulus and P. persica, is of greater significance compared to rangeland and agricultural land uses in enhancing soil fertility and creating favorable biological conditions. As a result, this research provides valuable insights into the impact of different land uses on the characteristics of the organic and mineral soil layers in mountainous habitats. The information obtained can be instrumental in guiding natural resource managers and offering practical assistance in decision-making processes.
N. Azadi; F. Raiesi
Abstract
Introduction: Heavy metals contamination of soils is an important environmental concern which has specially long-term hazardous effects on soil biogeochemical and microbiological properties (including microbial and enzyme activity, microbial community structure, and the contents of organic compounds). ...
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Introduction: Heavy metals contamination of soils is an important environmental concern which has specially long-term hazardous effects on soil biogeochemical and microbiological properties (including microbial and enzyme activity, microbial community structure, and the contents of organic compounds). Among heavy metals, cadmium (Cd) and lead (Pb) are the two highly toxic, non-biodegradable and often coexisted anthropogenic pollutants in contaminated sites. Numerous earlier studies have demonstrated a detrimental influence of Cd and Pb, both individually and jointly, on microbial and biochemical properties through reduction of microbial activity, microbial biomass and enzyme activity in polluted soils. Metal co-contamination has a greater negative effect on soil microbial community and enzyme activity compared to individual ones. Although the individual effects of Cd and Pb on soil biological functions are generally well-known, their combined effects on microbial growth, population and functions are largely uncertain. The main aim of this study was to investigate the interactive effects of Cd and Pb pollutants on biochemical and microbiological properties in a contaminated soil. It was hypothesized that combined Cd and Pb would increase mobility and availability of Cd and Pb, which subsequently results in further reductions in soil biochemical and microbiological properties. Materials and Methods: The study was conducted under controlled laboratory conditions. A factorial experiment with two levels of cadmium (0 and 10 mg kg-1) and two levels of lead (0 and 150 mg kg-1) was conducted using a completely randomized design with three replications. The soil was artificially spiked with cadmium chloride and lead chloride to attain the above mentioned concentrations. To reactivate the microbial population and for the aging effect, soil moisture was set at 70% of field capacity, and containers were pre-incubated at room temperature for 20 days. Soil samples were incubated under standard conditions (70% of field capacity and 25±1 oC) for 120 days. At the end of the soil incubation the concentration of DTPA-TEA (diethylene triamine penta acetic acid-triethanol amine)-extractable Cd and Pb, biochemical and microbiological properties including nitrification rate (NR), cumulative N mineralization (CNM), cumulative C mineralization (CCM), microbial biomass C (MBC), microbial biomass N (MBN), arginine ammonification (AA), basal respiration (BR), substrate (glucose)-induced respiration (SIR), metabolic quotient (qCO2) and the activities of soil urease (URE), alkaline phosphatase (ALP), arylsulphatase (ARY), dehydrogenase (DEH), catalase (CAT) and fluorescein diacetate hydrolysis (FDA) were determined. In this experiment, the Bliss independence model was used to determine the type and nature of the interaction between Cd and Pb pollution (i.e., synergistic and antagonistic). Results and Discussion: Results showed that the DTPA-extractable metal (Cd and Pb) concentrations were considerably higher under the combined metals compared with the single-metals. In co-contaminated soils, a metal may contribute to release of other metals to soil solution and consequently would enhance the availability of the released metals. Compared to individual metal, the qCO2 was greater in Cd+Pb contaminated soil. Microbial and biochemical properties (MBC, MBN, AA, NR, CNM, CCM, BR, SIR) and enzyme activity (URE, ARY, ALP, DEH, CAT and FDA) significantly decreased in the presence of Cd or Pb pollutant than the control. Generally, the negative effects of Cd and Pb co-existence on biochemical and microbiological properties were higher than Cd or Pb alone because of synergistic interaction in the metal combinations. The results of Bliss independence model indicated the synergistic effect of Cd and Pb on microbial and biochemical functionalities in metal-co-contaminated soils. In soil ecosystem, heavy metals exhibit toxicological effects on soil microbes which may lead to the decrease of their function and activities. Conclusion: Heavy metals can effectively change the soil biochemical and microbiological properties. This study provided strong evidence revealing that combined Cd and Pb can increase the mobility and availability of heavy metals, and intensify their toxicity effects on microbial community and enzyme activity in co-contaminated soils. The co-existence of Cd and Pb reduced soil biochemical and microbiological properties more than their individual presence. Soil microorganisms are an important indicator of soil fertility and health and thus would improve the accuracy of the ecological risk assessment of toxic metals at multi-metal contaminated sites. However, further information on responses of microbial indicators to the joint effect of heavy metals under long-term and realistic field conditions is required.
