بومشناسی جنگلهای ایران (Oct 2024)
Effect of Humic Acid and Cattle Manure on Stomatal Conductance, Photosynthesis, and Growth Variables of White Mulberry Seedlings in the Nursery Condition
Abstract
Extended Abstract Background: In contemporary times, the increasing population growth in large urban areas, industrial development in these cities, and the need for expanding urban green spaces and green belts have drawn the attention of managers to the use and cultivation of multipurpose tree species more than ever before. In many advanced countries, the use of chemical fertilizers has been discontinued in urban green spaces, parks, agriculture, and horticulture. The major reasons for this include undesirable environmental effects, disruption of soil chemical balance and structure, disruption of the ecology of plant and animal communities, and pollution of freshwater bodies. For this reason, the utilization of various organic fertilizers has been highlighted as one of the important strategies in improving horticultural and agricultural production and reducing the risk of environmental pollution, especially pollution of surface and groundwater resources. Humic acid (HA) is among the main types of organic fertilizers and a type of stabilized organic acid derived from the main compounds of humus, considered one of the most abundant organic compounds in nature. The use of HA for plants can directly and indirectly promote better plant growth, thereby increasing production levels and improving crop quality. Therefore, the present study aimed to assess the possibility of enhancing the growth and viability components of white mulberry seedlings as the most commonly used tree species for planting in the green belt of Mashhad using HA fertilizer and animal manure. Methods: For this research, two-year-old and uniform-sized mulberry seedlings were prepared as bare-root. Then, they were transferred to prepared beds in the green belt nursery of Mashhad for planting in pits with planting distances of 1.5 × 1.5 m in a completely randomized design. In five separate experimental plots, the nursery soil was thoroughly and uniformly mixed with animal manure. Subsequently, HA fertilizer in liquid form (at 50 and 300 mg/l) was mixed with the soil in two plots in addition to the animal manure. In the other two plots, foliar spraying at 50 and 300 mg l-1 on the leaf surfaces of the seedlings was carried out at the beginning of the growing season. Only animal manure treatment was considered for the seedlings in the fifth plot. Ten seedlings were selected for each treatment as replicates for examination. The seedlings were irrigated uniformly throughout a six-month growing period for measurement purposes. The growth and physiological characteristics of the seedlings, including plant height, collar diameter, root length, leaf and branch numbers, dry weight of aerial and root parts, gas exchange rates, photosynthesis rate, and seedling survival, were measured and statistically compared after 6 months of applying the treatments. To measure biomass, the seedlings were carefully removed from the soil, and the soil was washed from around the roots, followed by counting the number of branches and leaves. Each seedling was then divided into two parts of roots and stems, which were dried at 70 °C for 48 h and weighed using a digital scale. Finally, the data were analyzed in a completely randomized design, and their means were statistically compared using Tukey's test. The gas exchange rates (stomatal conductance) and photosynthesis rate in outdoors and under natural conditions of temperature, light, and relative humidity were measured using a portable device for gas exchange measurements. For this purpose, 3-6 mature leaves were selected from each replicate. All measurements were conducted between 9 am and 12 pm on a sunny day with a light intensity of 1400 µmol m-2 s-1. Results: The HA treatment added to the soil at a concentration of 300 mg/l resulted in the highest average values of the variables, namely the highest values of radial growth (3.2 mm), sapling height growth (35.1 cm), number of leaves (45), number of branches (16), dry root weight (31.3 g), and shoot weight (38.1 g). A comparison of physiological variables, such as photosynthesis intensity (14.5 μmol m-2 s-1) and stomatal conductance rate (0.23 mol m-2 s-1), revealed that the treatment with 300 mg/l of HA added to the soil led to the highest values. Subsequently, the treatment of 50 mg l-1 of HA added to the soil and then foliar spraying with an HA solution of 300 mg l-1 showed better effects than the other treatments. Overall, increasing HA in the soil resulted in better performance than foliar spraying on the leaf surface of white mulberry seedlings. Animal manure created the lowest averages in all evaluated variables. Conclusion: The positive effects of HA on plant growth and biomass are attributed to its ability to increase water and nutrient absorption by plants, as well as its pseudo-hormonal effects on plants. Based on the results of the present study, HA application positively influenced growth characteristics, photosynthesis intensity, and biomass increase (variables such as leaf number, branch number, sapling length growth, radial growth, root growth, and aerial parts growth). Therefore, adding HA fertilizers to the soil during mulberry planting is highly recommended in urban green spaces, horticulture, and urban green belts.
