Changes in root characteristics and soil biochemical activities under the influence of the Catena landscape in western Mazandaran

Background and objectives: Rangelands represent one of the most expansive ecosystems globally and are instrumental in preserving ecological equilibrium. Landform significantly influences soil formation and plays a crucial role in the variability of soil properties. "Catena" is one of the various landform types, consisting of five positions: summit, shoulder, back, foot, and toe slopes. Topographic variations in the Catena influence water and nutrient availability, root distribution, and soil properties, ultimately affecting vegetation cover, biological processes, and soil quality. In this context, the different positions of a Catena are key factors in shaping the relationships between soil and root characteristics. Although rangelands constitute a substantial portion of semi-arid landscapes, comprehensive information on semi-arid rangeland soils, particularly across different landform types, is scarce. Semi-arid ecosystems are among the most sensitive and fragile regions due to their specific climatic conditions. This study investigates how landform influences root traits and soil enzymes in a semi-arid rangeland landscape located in the mountainous region of northern Iran, thereby deepening our understanding of the Catena concept. Roots (fine and coarse roots) occupy a very large part of the components of the basement in different positions of the Catena. The landform can have many effects on the biomass of roots, which can vary in different situations. Catena positions determine soil moisture and replenishment, which in turn affects the amount of root biomass. The roots of plants are made up of two main parts: fine roots, which are less than 2 mm in diameter, and coarse roots, with a diameter of more than 2 mm. These two parts play an important role in the underground structure of the soil and constitute a significant part of its composition in natural ecosystems. Fine roots play a very important role in the nutrient cycle. Coarse roots make plants strong due to their larger size and have a slower rate of return to the soil compared to fine roots, but it affects the performance of habitats. Biochemical activities are significantly sensitive to other physical and chemical properties of soils, which consequently makes them a suitable indicator for evaluating soil quality in different landforms. Soil enzymes during the chemical catalysis process are a strategy for replenishing plants and organic matter in the soil.
Materials and methods: For this purpose, the Gilkola region in the Kojur district of Mazandaran province was selected as the study area. Initially, three V-shaped and three Ʌ-shaped Catenas were determined in this area. Within these landforms, sampling was conducted at each of the five positions along the cross-section of the Catena. Soil samples were collected from an area of 30×30 cm at three depths: 0-15 cm, 15-30 cm, and 30-45 cm. In total, 270 soil samples were collected from the studied structures and transported to the laboratory for analysis. After transporting the soil samples to the laboratory, coarse- and fine-roots were separated from the samples (based on the depth of 0-45 cm) and washed with a 2 mm sieve. Air-dried soil samples and root samples were placed in an oven at 70 °C for 24 hours and dried. After sample preparation, root characteristics were measured, including root biomass by weighing, carbon by combustion, nitrogen by mineralization, phosphorus by Olsen method, potassium, calcium and magnesium by atomic absorption method. Biochemical activities of enzymes were incubated under standard conditions and in a sufficient medium, and based on colorimetric measurement of the product released from the enzyme, the enzyme activity rate was determined using standard methods. Soil characteristics were analyzed using the F test and in the form of a double-split plot design. Statistical analysis of all data was performed using SPSS version 20 software. Also, multivariate analysis and principal component analysis (PCA) were used to investigate the relationship between the shape, positions and different depths of the catena using the PC-ORD program.
Result: The results of this research showed that the land form had significant effects on the characteristics studied. The results showed that the biomass (645.57 g/m2) and carbon (18.70%) of the coarse roots, fine roots phosphorus (2.32%) and calcium (0.86%) of the fine roots were higher in the V-shaped Catena than in the Λ-shaped Catena. Also, the highest values of coarse root characteristics including biomass (801.16 g/m2), carbon (24.30%), phosphorus (1.62%), and calcium (0.46%) were observed at the toe position of the Catena slope. The highest values of biomass (35.92 g/m2), nitrogen (0.44%), phosphorus (2.32%), potassium (1.39%), calcium (0.86%) and magnesium (0.69%) of the fine roots were observed in the V-shaped Catena. fine root biomass (47.24 g/m2) and their nutrients (34.30% carbon, 0.54% nitrogen, 3.02% phosphorus, 1.55% potassium, 1.07% calcium, and 0.87% magnesium) were highest in the toe slope of V-shaped Catena. In addition, the results of root measurements showed that its biomass (502.39 g/m2), carbon (24.71%), nitrogen (0.38%), phosphorus (1.89%), potassium (1.19%), calcium (0.62%), and magnesium (0.45%) were highest in the V-shaped Catena, and also in the toe slope position (636.81 g/m2, 29.30%, 0.44%, 2.32%, 1.30%, 0.77%, and 0.59%) respectively. The results obtained from the measurement of the enzymes studied showed that in the V-shaped Catena, the highest amounts of acid phosphatase (µg PNP g−1 h−1 67.260), arylsulfatase (µg PNP g−1 h−1 89.207) and invertase (µg Glucose g−1 3 h−1 40.229) and the highest amounts of urease (µg NH4+ -N g−1 2 h−1 04.21), acid phosphatase (µg PNP g−1 h−1 35.402), arylsulfatase (µg PNP g−1 h−1 55.350) and invertase (µg Glucose g−1 3 h−1 77.307) were in the toe slope, respectively, and in the 0-15 cm layer of soil, respectively (µg NH4+ -N g−1 2 h-1 67/17), (µg PNP g−1 h −1 61/267), (µg PNP g−1 h −1 22/213) and (µg Glucose g−1 3 h −1 01/224) had the highest activity.
Conclusion: The results of this study indicate that different positions of the Catena, as a topographic unit, have a significant impact on soil properties, vegetation cover, and belowground activities. In the V-shaped Catena, lower slope positions have better soil conditions, such as moisture retention and nutrient availability, which provide favorable conditions for plant growth and biological activities. In these areas, vegetation cover is better than in the upper slope positions and helps protect the soil from erosion. In contrast, in the upper slope positions, due to poor soil conditions, vegetation cover is weaker, and soil erosion can disrupt biological activities. The summit and shoulder positions of the Catena, due to their natural restorative capacity, could be suitable targets for soil restoration and rehabilitation operations. Indeed, it may be thought that the accumulation of organic matter, leaching of nutrients, and creation of a favorable microclimate can enhance biological activities, whereas the reduction of vegetation cover in top positions has detrimental effects on belowground components. The interaction between these variables can provide valuable insights into soil fertility dynamics and ecosystem functioning. In conclusion, the findings of this study demonstrate the necessity of maintaining the foot and toe positions of the Catena to enhance soil fertility and overall soil health. These findings could contribute to improving natural resource management and nutrient cycling in the mountainous regions of northern Iran.