Soil science
S.S. Hosseini; F. Rejali; P. Keshavarz
Abstract
Introduction
Water scarcity is a major challenge in Iran, with annual rainfall averaging 235 to 260 mm, only a third of the global average. Wheat, a staple crop in Iran, faces severe yield reduction under drought conditions. Utilizing biofertilizers like plant growth-promoting rhizobacteria ...
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Introduction
Water scarcity is a major challenge in Iran, with annual rainfall averaging 235 to 260 mm, only a third of the global average. Wheat, a staple crop in Iran, faces severe yield reduction under drought conditions. Utilizing biofertilizers like plant growth-promoting rhizobacteria (PGPR) and arbuscular mycorrhizal (AM) fungi could help enhance water use efficiency (WUE) and yield in such environments. However, the effectiveness of biofertilizers varies based on several factors, including the type of biofertilizer (bacterial or fungal), the strain or species used, and the formulation (solid or liquid). Despite the established benefits of both PGPR and AM fungi in enhancing drought tolerance and WUE, there is a lack of comparative studies that examine the specific performance of bacterial versus fungal biofertilizers and their formulations under varying levels of water stress. Thus, the objectives of this study are as follows: 1) to identify the most suitable type of biofertilizer (bacterial or fungal) for improving wheat yield and WUE under drought conditions in Mashhad's climatic conditions; 2) to determine the effect of ACC deaminase enzyme on the efficiency of PGPR in enhancing wheat yield and WUE; 3) to compare the performance of AM fungal biofertilizers in two formulations (powder and liquid) and between single-species and multi-species inoculants.
Material and Methods
The experiment was conducted as a split-plot design with three replicates, where irrigation levels constituted the main plots, and biofertilizer treatments formed the subplots. The irrigation treatments included full irrigation (100% of wheat’s water requirement), mild drought stress (85%), and severe drought stress (65%). The biofertilizer treatments were: no biofertilizer (F1), serving as a control; Pseudomonas fluorescens producing ACC-deaminase (F2); P. fluorescens without ACC-deaminase (F3); AM fungi (Rhizophagus irregularis) in liquid form (F4); and (5) AM fungi (R. irregularis, Funneliformis mosseae, and Claroideoglomus etunicatum) in powdered form (F5).
Results and Discussion
Both irrigation levels and biofertilizer types had significant impacts on root colonization, yield, and WUE. Reducing irrigation from 100% to 85% and 65% of crop water requirements significantly reduced root colonization across all treatments. Among the bacterial treatments, only P. fluorescens producing ACC-deaminase (F2) showed a significant positive effect under severe drought (65% irrigation). This treatment increased grain yield by 9%, biological yield by 7%, and WUE by 6.8% compared to the control (F1). The presence of ACC-deaminase likely contributed to mitigating the effects of drought-induced ethylene, promoting better root growth and nutrient uptake under water stress. In contrast, P. fluorescens without ACC-deaminase (F3) did not significantly improve yield or WUE, emphasizing the importance of ACC-deaminase in promoting drought tolerance. Fungal biofertilizers outperformed bacterial treatments in grain and biological yield, as well as WUE. Under severe drought, powdered AM fungi (F5) increased grain yield by 26% and biological yield by 21% compared to the control, and WUE based on grain yield improved by 26%. This superior performance of AM fungi, particularly in powdered form, can be attributed to their ability to enhance nutrient and water uptake under drought conditions. These findings corroborate earlier studies that demonstrated AM fungi's ability to improve crop yield and WUE under drought stress by enhancing water uptake, nutrient availability, and improving the plant's physiological responses, such as maintaining cell membrane stability and increasing antioxidant activity. The powdered formulation of AM fungi (F5) showed greater effectiveness than the liquid form (F4). The higher colonization rates and performance in yield improvement may be due to the inclusion of multiple fungal species in the powdered form. The performance differences between the liquid and powdered AM fungi formulations may also be influenced by the physical properties of the biofertilizer since powdered inoculants are most effective when applied to the seeds of grasses like wheat and barley, as the structure of these seeds allows for better adhesion of the powder.
Conclusion
In conclusion, among the bacterial biofertilizers, only P. fluorescens producing ACC-deaminase significantly enhanced plant performance under severe drought, underscoring the importance of ACC-deaminase in alleviating drought stress. However, fungal biofertilizers, especially in powdered form, were more effective overall in improving yield, biological productivity, and WUE under varying levels of water stress. This research confirms that the application of AM fungi can serve as an effective strategy for improving wheat yield and increasing WUE in the climatic conditions of Mashhad. Overall, the observed differences in the effectiveness of these biofertilizers suggest that the appropriate selection of both type and formulation of biofertilizers can significantly contribute to managing water stress and improving crop production.
