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.
seyed sajjad hosseini; Amir Lakzian; Akram Halajnia
Abstract
Introduction: Application of EDTA may increase the heavy metal availability and phytoextraction efficiency in contaminated soils. In spite of that, it might also have some adverse effects on soil biological properties. Metals as freeions are considered to be severely toxic, whereas the complexed form ...
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Introduction: Application of EDTA may increase the heavy metal availability and phytoextraction efficiency in contaminated soils. In spite of that, it might also have some adverse effects on soil biological properties. Metals as freeions are considered to be severely toxic, whereas the complexed form of these metalswith organic compounds or Fe/Mn oxides may be less available to soil microbes. However, apart from this fact, some of these compounds like EDTA and EDTA-metal complexes have low bio- chemo- and photo-degradablity and high solubility in their own characteristics andable to cause toxicity in soil environment. So more attentions have been paid to use of low molecular weight organic acids (LMWOAs) such as Citric acid because of having less unfavorable effects to the environment. Citric acid increases heavy metals solubility in soils and it also improves soil microbial activity indirectly. Soil enzymes activity is a good indicator of soil quality, and it is more suitable for monitoring the soil quality compared to physical or chemical indicators. The aims of this research were to evaluate the changes of dehydrogenase, urease and alkaline phosphomonoesterase activities, substrate-induced respiration (SIR) and Pb availability after EDTA and citric acid addition into a contaminated soil with PbCl2.
Materials and Methods: An experiment was conducted in a completely randomized design with factorial arrangement and three replications in greenhouse condition. The soil samples collected from surface horizon (0-20 cm) of the Typic haplocalsids, located in Mashhad, Iran. Soil samples were artificially contaminated with PbCl2 (500 mg Pb per kg of soil) and incubated for one months in 70 % of water holding capacity at room temperature. The experimental treatments included control, 3 and 5 mmol EDTA (EDTA3 and EDTA5) and Citric acid (CA3 and CA5) per kg of soil. Soil enzymes activity, substrate-induced respiration and Pb availability of soil samples were determined by standard methods after 7, 14, 21 and 28 days of chelates addition.
Results and Discussion: The soil texture was loam and the indigenous Pb content was 25.55 mg kg-1. The soil pH was 7.4 and electrical conductivity of saturated extraction measured 2.5 dS m-1. The soil carbonate calcium was 14% and the content of organic carbon and essential nutrients were low. The results showed that EDTA3 and EDTA5 treatments increased Pb availability by 2.17% and 10% compared to control treatment but CA3 and CA5 treatments decreased it by 3.8% and 15.7% respectively. The Pb availability in control and EDTA5 treatments did not change during the incubation time. The available Pb concentration dropped sharply during the incubation time in EDTA3, CA3 and CA5 treatments. The reduction rates in CA3 and CA5 treatments were more than EDTA3 treatment. This may be due to the high stability and low biodegradability of EDTA than biodegradable chelators and low molecular weight organic acids. The results showed that urease and dehydrogenase activities were significantly reduced in EDTA3 and EDTA5 treatments compared to control treatment. Urease and dehydrogenase activities were decreased with the increase of EDTA concentration. Alkaline phosphomonoesterase activity was not affected by the EDTA3 and EDTA5 treatments. In CA3 and CA5 treatments, dehydrogenase and alkaline phosphomonoesterase activities significantly increased with increasing the concentration of citric acid. CA5 treatment showed a prominent effect on urease activity compare to CA3 treatment. The soil enzyme activities increased with incubation time. It seems that reduction in Pb availability causes an increase of soil enzymes activities. Significant negative relationships were found between soil enzymes activities and available Pb concentration (dehydrogenase activity (r=-0.906, P
