| چکیده انگلیسی مقاله |
This study evaluated the effects of humic acid and mycorrhizal species on chlorophyll index, quantum yield, malondialdehyde (MDA) content, and wheat traits under varying irrigation regimes using a factorial experiment in a randomized complete block design with three replications. Conducted at the University of Mohaghegh Ardabili research farm (38°15ʹ N, 48°15ʹ E) during 2018–2019, treatments included three irrigation levels (full irrigation, severe water limitation at booting [BBCH 45], and moderate limitation at heading [BBCH 59]) and eight combinations of humic acid and mycorrhizal species (Glomus intraradices, G. mosseae, their combinations, and a control). Severe water limitation without amendments resulted in the highest electrical conductivity (341.1 µS/cm), MDA (0.17 µmol/g FW), and H2O2 (0.36 µmol/g FW). At the same treatment, full irrigation with humic acid and both mycorrhizal species yielded the lowest values (115.4 µS/cm, 0.019 µmol/g FW, and 0.14 µmol/g FW, respectively). Maximum leaf protein (14.09%) and grain yield (951.2 g/m2) were recorded under full irrigation with combined treatments, compared to minimum values (11.3% and 701.43 g/m2) under severe drought without amendments. Among severe water limitations, humic acid with G. mosseae and G. intraradices increased grain yield by ~24% over the control. These results underscore the efficacy of bio-organic fertilizers in enhancing wheat yield and drought tolerance by improving agrophysiological traits.
Introduction
Water scarcity represents one of the most significant abiotic stressors affecting plant growth and productivity on a global scale. This condition disrupts critical physiological processes, including hormone synthesis, transpiration, photosynthesis, and nutrient translocation, while simultaneously elevating ethylene concentrations in roots and altering metabolic activities. Mitigating the deleterious effects of water deficit by applying humic acid offers a promising, cost-effective, and sustainable strategy for promoting resilient agricultural systems. Additionally, bio-organic fertilizers, such as arbuscular mycorrhizal fungi (AMF), constitute an effective approach to bolstering plant tolerance to environmental stresses. AMF enhances drought resistance and optimizes plant growth by maintaining ionic equilibrium, enhancing photosynthetic apparatus functionality, and improving photosynthetic efficiency, quantum yield, and chlorophyll content.
The combined application of humic acid and mycorrhizal inoculation is hypothesized to be an environmentally sustainable method for improving drought tolerance in crops such as wheat. Accordingly, this study seeks to evaluate the effects of humic acid and AMF on key physiological parameters—namely, chlorophyll index, quantum yield, malondialdehyde levels, and selected agronomic traits—in wheat subjected to varying irrigation regimes.
Material and Methods
This factorial experiment was a randomized complete block design with three replications at the Faculty of Agriculture and Natural Resources research farm, University of Mohaghegh Ardabili, during the 2018–2019 growing season. The experimental site is located at 38°15ʹ N latitude and 48°15ʹ E longitude, at an elevation of 1,350 m above mean sea level. The region is characterized by a wet climate zone with severe winters and hot summers in northwestern Iran, classified under the Köppen system as a semiarid, cold temperate climate. The experimental factors comprised irrigation at three levels—full irrigation, irrigation withholding at 50% of the booting stage (severe water limitation, BBCH code 45), and irrigation withholding at 50% of the heading stage (moderate water limitation, BBCH code 59)—and the application of humic acid combined with mycorrhizal species at eight levels: Glomus intraradices, G. mosseae, combined G. intraradices and G. mosseae, humic acid alone, humic acid with G. intraradices, humic acid with G. mosseae, humic acid with both G. intraradices and G. mosseae, and a control (no humic acid or mycorrhizal inoculation).
Each experimental plot consisted of five 2-m-long rows, with 1.5-m unplanted buffers separating plots and blocks. Mycorrhizal inoculum (G. mosseae) was sourced from Zist Fanavar Turan Corporation, and soil treatments were applied following the protocol of Gianinazzi et al. (2001). Chlorophyll index measurements were obtained using a SPAD-502 device (Konica Minolta Sensing, Inc., Japan), with three readings per plot taken from the top, middle, and base of leaves, and the mean value per plot was recorded. Quantum yield was assessed on the uppermost fully expanded leaf using a chlorophyll fluorometer (Optic Science-OS-30, USA). For this measurement, plants were dark-adapted for 20 minutes using specialized clamps, and fluorescence was quantified at 1000 µmol photons m-2 s-1. Grain yield was determined by harvesting the three central rows (equivalent to 1 m²) of each plot. Data were subjected to analysis of variance (ANOVA) and mean comparisons using the SAS software package (version 9.12). Significant differences among main effects and interactions were evaluated using the least significant difference (LSD) test at P ≤ 0.05.
Results and Discussion
The results indicated that the highest values of electrical conductivity (341.1 µS/cm), malondialdehyde (MDA), and hydrogen peroxide (H2O2) content (0.17 and 0.36 µmol/g fresh weight [FW], respectively) were recorded under severe water limitation (irrigation withholding at the booting stage) in the absence of humic acid and mycorrhizal inoculation. Conversely, the lowest values for these parameters (115.4 µS/cm, 0.019, and 0.14 µmol/g FW, respectively) were observed under full irrigation with the combined application of humic acid, Glomus mosseae, and G. intraradices. The maximum leaf protein content (14.09%) and grain yield (951.2 g/m²) were achieved under full irrigation with the combined application of humic acid, G. mosseae, and G. intraradices. The minimum values for these traits (11.3% and 701.43 g/m2, respectively) were recorded under irrigation withholding at the booting stage without humic acid or mycorrhizal application. Notably, under severe water limitation (irrigation withheld at the booting stage), the combined application of humic acid with G. mosseae and G. intraradices resulted in a grain yield increase of approximately 24% compared to the control (no humic acid or mycorrhizal application) at the same irrigation level.
Conclusion
Based on the findings, bio-organic fertilizers' individual and combined application (humic acid and mycorrhizae) can enhance wheat grain yield under water-limited conditions by improving key agrophysiological traits.
Acknowledgments
Funding for the present research was provided by the Mohaghegh Ardabili University of Iran. The authors gratefully acknowledge the Mohaghegh Ardabili University. |