Soil science
Sahar Mehrnoosh; Ali Beheshti Ale Agha; Fatemeh Rakhsh; Morteza Pourreza; Ali Akbar Safari Sinegani
Abstract
IntroductionThe maintenance of planted forests in arid and semi-arid lands is important. Soil formation in forest ecosystems is different with different tree species. Tree species have a direct and indirect effect on soil organisms. Forest ecosystems change their species composition and abundance of ...
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IntroductionThe maintenance of planted forests in arid and semi-arid lands is important. Soil formation in forest ecosystems is different with different tree species. Tree species have a direct and indirect effect on soil organisms. Forest ecosystems change their species composition and abundance of microorganisms, and consequently their biogeochemical cycles. The accumulation of vegetation biomass and the improvement of soil fertility can play a significant role in soil restoration.Materials and MethodsIn order to investigate the biological characteristics of the soil from 5 treatments, including agricultural (dry farming and relatively poor lands that are usually cultivated barley and wheat and have low productivity), pasture (pastures with minimal vegetation and high slopes that are affected by overgrazing have been changed to barren lands), forest with Acacia type (under and outside the crown), forest with the Cupressus arizonica type (under and outside the crown) and forest with the Pinus brutia type (under and outside the crown) randomly. Sampling was done in 3 repetitions from the 0 to 5 cm layer. The statistical sampling design of this research was completely random, in which, according to the type of afforested species, two types of coniferous forest stands (including Cupressus arizonica and Pinus brutia) and one broadleaf stand (Acacia species) were selected. Also, the area under the crown trees and outside the crown trees was also investigated. Soil samples were sampled with sterile equipment and crushed through a 4-mm sieve. Fresh and moist soil was kept at 4 °C temperature for soil biological tests. Microbial biomass carbon, soil basal respiration (197 days), substrate-induced respiration, and metabolic quotient were measured. Streptomycin sulfate was used to measure fungal respiration and cycloheximide was used to measure bacterial respiration. The activities of urease, acid, and alkaline phosphatase enzymes were determined. After measuring the biological properties of the soil, the normality of the data was checked by the Anderson–Darling test, and the homogeneity of the variance of the treatments was checked by using Levene's test. Analysis of data variance was done using One-Way ANOVA and average data comparison was done using Duncan's test at 5 and 1% probability levels (SAS 9.4 and SPSS 26).Results and DiscussionThe results of soil biological characteristics analysis showed that the highest values of soil respiration and amount of consumed organic matter, substrate-induced respiration, microbial biomass carbon, enzyme activities, and fungal respiration were measured in conifers. Although the amount of these features was also significant in broadleaf trees, they had significant differences. In this study, the high soil respiration rate in coniferous covers compared to broadleaf can be due to the high organic carbon content of the soil in this cover. According to the results of substrate-induced respiration in different coatings, likely the activity of microorganisms involved in the decomposition of organic matter in the studied habitats had a significant difference; Therefore, different coatings can affect the population of soil microorganisms as the main source of decomposition and emission of carbon dioxide by changing the quantity and quality of organic matter and other factors. Also, the highest values of metabolic quotient and bacterial respiration were observed in agricultural and pasture covers. A higher metabolic quotient in these covers indicates a decrease in the efficiency of the use of leaf litter by the soil microbial community. In general, the metabolic quotient in the bacterial community is higher than the fungal community; Therefore, it seems that the predominance of the bacterial population in agricultural and pasture cover has caused this index to increase, although plowing and cultivation, and disturbance of these covers have caused stress to this bacterial community and as a result increased the metabolic quotient deficit in these covers.ConclusionThe results of this research showed that the type of planted tree species causes significant changes in the biological characteristics of the soil. The current research shows that the forest, whether coniferous or broadleaf, had the highest values of enzyme activities, basal respiration, substrate-induced respiration, microbial biomass carbon, and the lowest values of metabolic quotient compared to agricultural and pasture covers. Afforestation increases biological activity and possibly the number and diversity of microorganisms, and improves soil characteristics in the long term. In agriculture and pasture land, due to the destruction of soil and aggregates by agricultural activities such as plowing or excessive livestock grazing, the amount of organic carbon and the activity of microorganisms decreases, and with the decrease of other soil characteristics, the quality of the soil decreases over time. From this research, it can be concluded that the planting of forest species in the soils of degraded areas in the long term can increase soil organic carbon due to high-quality leaf litter, and as a result, increase permeability and soil moisture. Increasing soil organic carbon increases the activity of microorganisms, and in the long term, it will improve various soil characteristics. Planting forest plants in the natural areas of the country, which were destroyed due to the change of use to agriculture and indiscriminate cultivation and finally abandoned, can improve the characteristics of the soil and, as a result, establish the native vegetation of the region, and increase the permeability of water in the soil, the risk of soil erosion, floods, etc. reduce.
elham sadeghi; fayez raiesi; Alireza Hosseinpour
Abstract
Introduction: Soil, as an important component of terrestrial ecosystems, plant growth media, and a habitat of diverse living organisms commonly encounters a variety of abiotic stresses. Soil microorganisms play an important role in maintaining soil quality and functioning, since they are responsible ...
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Introduction: Soil, as an important component of terrestrial ecosystems, plant growth media, and a habitat of diverse living organisms commonly encounters a variety of abiotic stresses. Soil microorganisms play an important role in maintaining soil quality and functioning, since they are responsible for the decomposition of dead organic material, nutrient cycling and degradation of hazardous organic pollutants. Metal toxicity and salinity are the major abiotic stresses affecting soil microbial activity and community structure in many areas of the world, in particular arid regions. Anthropogenic activities have increased the concentration of heavy metals and soluble salts in soil, resulting in a major constrain for soil microbial performance and functions. Furthermore, soil microbial activity and biochemical processes are often limited by substrate availability in arid areas due to the low organic inputs. Although the individual effects of salinity and metal toxicity stresses on soil biological activity 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 salinity and cadmium (Cd) Pollution on microbial respiration and biomass in a calcareous soil treated with plant residue. It was hypothesized that salinity would increase mobility and availability of Cd with subsequent reductions in microbial activity and biomass, and that addition of plant residue would modify these salinity effects.
Materials and Methods: This study was conducted under controlled laboratory conditions at Shahrekord University. A factorial experiment with two levels of cadmium (0 and 30 mg kg-1), three levels of salinity (1.35, 7.5 and 10 dS m-1) and two levels of plant residue (with and without alfalfa residue) was conducted using a completely randomized design with four replications. Using cadmium chloride salt, the soil was contaminated, and subsequently amended with alfalfa residue (1%, w/w). After thorough mixing of soil and plant residue, salinity treatments were applied using NaCl salt. 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 4 weeks. The samples were then incubated at 25±1 oC for 98 days. Soil carbon (C) mineralization (microbial respiration) was measured weekly, and available Cd and microbial biomass C were measured at monthly intervals. In this experiment, the Bliss independence model was used to determine the type and nature of the interaction between salinity and pollution (synergistic and antagonistic).
Results and Discussion: The results showed that NaCl salinity increased the concentration of soil available Cd in both polluted and unpolluted soils over the experimental period, and the increases were greater at high than low salinity levels. This effect of salinity was less pronounced in residue-amended and unamended soils. In general, a strong synergistic effect of both stresses upon Cd availability was observed in residue-unamended soils while this effect was mostly antagonistic in residue-amended soils. This indicates that addition of plant residue to enhance soil organic matter may indirectly repress or lower salinity effect on Cd toxicity. Soil salinity decreased microbial biomass C and respiration with subsequent increases in specific respiratory quotient due to the increases in Cd solubility and availability. However, the changes in microbial properties were much lower in residue-amended and unamended soils. Addition of plant residue decreased the negative effects of both the individual and combined salinity and Cd pollution on microbial biomass and respiration. The interactive effect of these two stresses was mainly synergistic in residue-treated soils while it was antagonistic in residue-untreated soils. Overall, a strong synergistic effect occurred when both stresses were combined in the absence of plant residue while this effect was antagonistic in the presence of plant residue.
Conclusion: This study provided evidence that salinity could synergistically increase the mobility, bio-availability, and toxicity of Cd in Cd-polluted soils with C limitation. This was reflected by synergistic reductions in soil microbial biomass and respiration. However, addition of plant residue to increase soil organic matter lowered this effect of salinity, resulting in the antagonistic effects of salinity and pollution on soil microbial biomass and respiration. The reason for increase in the microbial activity in soils treated with plant residue was the increase of available substrate. As a result, using the plant residue increased the stimulatory effect of microbial activity. These findings point to the importance of providing adequate organic residues to enhance soil microbial performance and agricultural sustainability in polluted soils under salinity stress. However, further information on responses of microbial indicators to the joint effect of salinity and Cd toxicity is required.
Materials and Methods: This study was conducted under controlled laboratory conditions at Shahrekord University. A factorial experiment with two levels of cadmium (0 and 30 mg kg-1), three levels of salinity (1.35, 7.5 and 10 dS m-1) and two levels of plant residue (with and without alfalfa residue) was conducted using a completely randomized design with four replications. Using cadmium chloride salt, the soil was contaminated, and subsequently amended with alfalfa residue (1%, w/w). After thorough mixing of soil and plant residue, salinity treatments were applied using NaCl salt. 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 4 weeks. Next, the samples were incubated at 25±1 oC for 98 days. Soil C mineralization (microbial respiration) was measured weekly, and available Cd and microbial biomass carbon were measured at monthly intervals. In this experiment, the Bliss independence model was used to determine the type and nature of the interaction between salinity and pollution (synergistic and antagonistic).
Results and Discussion: The results showed that NaCl salinity increased the concentration of soil available Cd in both polluted and unpolluted soils over the experimental period, and the increases were greater at high than low salinity levels. This effect of salinity was less pronounced in residue-amended and unamended soils. In general, a strong synergistic effect of both stresses was observed on Cd availability in residue-unamended soils while this effect was mostly antagonistic in residue-amended soils. This indicates addition of plant residue to enhance soil organic matter may indirectly repress or lower salinity effect on Cd toxicity. Soil salinity decreased microbial biomass carbon and respiration with subsequent increases in specific respiratory quotient due to the increases in Cd solubility and availability. However, the changes in microbial properties were much lower in residue-amended and unamended soils. Addition of plant residue decreased the negative effects of both the individual and combined salinity and Cd pollution on microbial biomass and respiration. The interactive effect of these two stresses was mainly synergistic in residue-treated soils while it was antagonistic in residue-untreated soils. Overall, a strong synergistic effect occurred when both stresses were combined in the absence of plant residue while this effect was antagonistic in the presence of plant residue.
Conclusions: This study provided evidence that salinity could synergistically increase the mobility, bio-availability, and toxicity of soil Cd in Cd-polluted soils with carbon limitation. This was reflected by synergistic reductions in soil microbial biomass and respiration. However, addition of plant residue to increase soil organic matter lowered this effect of salinity, resulting in the antagonistic effects of salinity and pollution on soil microbial biomass and respiration. The reason for increase in the microbial activity in soils treated with plant residue was the increase of available substrate. As a result, using the plant residue increased the stimulatory effect of microbial activity. These findings point to the importance of providing adequate organic residues to enhance soil microbial performance and agricultural sustainability in polluted soils under salinity stress. However, further information on responses of microbial indicators to the joint effect of salinity and Cd toxicity is required.
