Water deficit significantly reduced the leaf relative water contents (LRWC)59. By Considering the high water absorption efficiency of the soil by peripheral hyphae36, using different types of mycorrhizal fungi could cause a substantial rise in the water status of inoculated plants, which is in association with non- mycorrhizal plants, under water- limited conditions97. Using organic fertilizers improves the water potential and maintains leaf turgor pressure, which is In agreement with this study result12. With respect to the green manure and vermicompost roles in soil organic matter and water content enhancement, dual-fertilized plants (Fm + v) indicated high percentage of LRWC in green manured plots.
This study results demonstrated that water stress inhibited mycorrhizal colonization in lingrain roots. These results are in agreement with earlier findings, proposing that mycorrhization will be decreased at low levels of soil moisture79. AMF are obligate biotrophic fungi, consequently very slow germination of spores and expansion of the hyphae or their complete inhibition under drought conditions could elucidate the drought adverse consequences on colonization32. Therefore, lower colonization can occur because of two reasons; the carbon obtainability reducing from host plants and also the fungal spore germination reducing in limited water conditions92. Up to the best of our knowledge, organic matter can affect the activity and frequency of soil microorganisms like AMF, which can increase the plant nutrients53. Vermicompost promotes the mycorrhiza colonization in the roots39,49,80. The highest percentage of AMF colonization (66%) in Ocimum basilicum roots was observed in using vermicompost + G. intraradices combination in comparison with control89. Therefore, the combination of vermicompost, mycorrhiza and green manure exhibit high root colonization under full irrigation condition in this research.
Nutrients absorption directly relates to the soil water status, thus the nutrient flow from soil to root decreases in moisture shortage conditions5. With respect to better solubility of phosphorus in irrigated soil, the phosphorus concentration of the leaves indicates a reduction along with water restriction, which is probably caused by reduced solubility, mobility (mass flow or propagation), transfer between the roots and branches, and also the absorption of P under drought conditions43,77. Mycorrhizal inoculation can increase the infection percentage and absorption range in the extramatrical mycelium, and after that increase the nitrogen absorption rate and phosphorus and improve the nutrition in plants63. However, inoculated plants under limited irrigation contained less nitrogen and phosphorus content, which may be due to drought constraints in mycelium development and reduced absorption range, in comparison with infected plants in well-watered condition52.
Green manure will increase the soil holding-capacity for water and nutrients content and mobility in the upper layer of soil, by providing organic matter. Plants can use these elements, and therefore increase their growth and productivity82. Moreover, there is an extensive record on the green manure advantages for nitrogen nutrition of succeeding crops21,45,68. Mineralized nitrogen from leguminous plant residues can provide considerable quantities of N to a subsequent crop73. Green manure effect on phosphorous availability could be caused from its P uptake and unavailable inorganic P changing to more available organic forms to the subsequent crop42. Furthermore, biodegradation of green manure remainders can produce bicarbonate (H2CO3) that can provide higher bio-available P for the plants by dissolving mineral P of the soil78.
Vermicompost provided high nutrition by balancing the nutrients, due to the fact that it contains all macro and some micro-nutrients. In regard with our results, vermicompost treatments increased the K uptake of Setaria grass75 and Lilium plant62. Moreover, vermicompost increased N percentage of spinach69 and leaf P content of corn (Gutiérrez-Miceli et al. 2008). Also, the available form of N (nitrate) in vermicompost is more than traditional composted manure84.
Water limitation reduced the leaf chlorophyll, and also carotenoid concentrations. One of the common symptoms of oxidative stress under drought conditions is the chlorophyll content reduction, which may be due to photo-oxidation and the pigment degradation2,66. This study results indicated that the amount of carotenoids, chlorophyll b and a significantly decreased under water limitation. These result are not consistent with several studies reported that carotenoid increased under water deficit conditions6,9.
Earlier researches9,46,47 approved our results that vermicompost application in soil brought about a remarkable growth in carotenoids content under water deficit condition. mycorrhizal inoculation resulted in the maintenance of a very high chlorophyll content relative to non-mycorrhizal plants in those plants subjected to late-season water limitation. This study results are in agreement with those reported by (Metwally et al. 2019)59. Using green manure can enhance the nitrogen availability, which can be used by lingrain in the chlorophyll production. Chlorophyll plays a crucial role in photosynthesis, such that increased chlorophyll formation will improve photosynthetic reactions and finally raise plant growth and production. Also, Subaedah and Aladin (2016)82 clarified the enhancement of chlorophyll content by using of green manure in maize, which is in parallel with our findings.
Amassing proline under stress conditions is identified as one of the plant remedies for osmotic regulation improving in the leaves. Proline plays a leading role during stress in the plant. In addition to a great osmolyte, it acts as a metal chelator, a signalling molecule and an antioxidant molecule81. Having a higher capacity for osmotic regulation is one of those plants characteristic with higher drought tolerance. In this study, AMF-treated plants indicated an enhanced accumulation of proline in water-limited condition. These results are in agreement with Gheisari Zardak et al. (2018)29 and Tyagi et al. (2017)87 findings. Consequently, AM plants can be physiologically more tolerant against drought and indicate more osmotic regulation during exposing to stress conditions. Chinsamy et al. (2013)17 demonstrated a substantial elevation in proline concentration within tomato grainlings under salinity stress by the use of vermicompost. Also, The same effect was observed with vermicompost in pomegranate14 and rice grainlings (García et al. 2012)28 under water limitation stress.
The lingrain plants exposure to drought stress could increase the TSS concentration. Results of a study accomplished by Masoudi-Sadaghiani et al. (2011)57 and Vijayalakshmi et al. (2012)90 have indicated that water constraints can elevate the concentration of TSS in the leaves. Increasing the TSS concentrations occurred in those plants that were treated with one of Fm and Fv, along with their combination in both irrigation regimes. However, under limited irrigation condition, TSS increasing was remarkably higher in mycorrhizal treatments and the presence of green manure. AMF enhance TSS and electrolyte concentrations in host plants. Furthermore, carbohydrates increasing in mycorrhizal plants may be attributed to increased photosynthetic carbon and enzymes activation reduction. Other researchers have reported increased carbohydrate in AM plants3,94. Furthermore, Tejada et al. (2008)86 reported that soluble carbohydrate contents of maize plants were the highest in Trifolium pratense L. amended soils. The increment of leaf TSS of plants treated with vermicompost was also reported by Tejada and Benítez (2011) and Salehi et al. (2016)76,85.
The main role of the GB could be considered as protecting the plasma membrane integrity from drought stress injury and contribution to osmotic regulation. Dual application of mycorrhiza and vermicompost increased the GB content under the water-limited conditions, and this indicating that the fertilizers could alleviate drought stress impacts. In addition, GB accumulation in cotton has been reported54 as an effective compatible solution under drought stress. Moreover, Hashem et al. (2015)41 reported that enhanced GB accumulation leads to better growth and salt tolerance, and after that improvement in the performance of photosynthetic traits.
Lower accumulation of H2O2 provides proof that increasing the antioxidant enzymes activity bring about the removal of ROS and the protection of host plants against oxidative stress26. A higher concentration of MDA in leaves, which can indicate the amount of peroxidation of membrane lipids, may be accompanied by higher H2O2 accumulation in drought stress plants30. Additionally, fertilized plants (Fm and Fv) indicated less MDA than control that indicates the fertilizers involvements in ROS metabolism14,61,72. In addition, mycorrhiza inoculation reduced the H2O2 and MDA concentration in foxtail millet leaves in drought33. In consistent with our results, Bidabadi et al. (2017)14 demonstrated a reduction in H2O2 content in vermicompost application. Moreover, using green manure would resulted in MDA and H2O2 concentrations reduction, and also along with that, enhancement of the catalase and peroxidase activities in water limitation. It appeared that green manure could impede H2O2 accumulation and lipid peroxidation in plants by increasing the water content of the soil. Limited-irrigation causes oxidative stress by increasing the production of ROS in plant cells, and oxidative damage is also eased by antioxidant enzymes like APX, CAT, and SOD74,83. Amongst anti-oxidants enzymes, SOD and CAT are recognized as the most frequently used detoxification enzymes, which play a major role in controlling excessive ROS, in collaboration with involved enzymes of the ascorbate–glutathione cycle10,15,38. In this study, the triple application of mycorrhiza, vermicompost and green manure increased the CAT activity in both irrigation conditions, consequently, they can facilitate quick sweeping of ROS especially H2O2, so that metabolic reactions are less affected. Earlier results confirmed that the mycorrhizal and vermicompost-applied plants indicated considerably higher enzyme activities in stress condition13,47,61,67.
Applying the green manure in soils at high doses increased maize grain yield in comparison with the control soil50. Similar results were obtained with the green manure application in wheat grain yield by Gruter et al. (2017)37.
Vermicompost along with biofertilizers-treated plots indicated a substantial increase in essential oil content, essential oil yield and biomass of Ocimum basilicum in comparison with control89. Similarly, Doan et al. (2015)19 and Goswami et al. (2017)34 reported an increase in grain yield by using vermicompost. Mycorrhizal symbiosis enhanced the grain and oil yields in comparison with non-mycorrhizal plants under both irrigation conditions. The results demonstrated that mycorrhizal colonization was a momentous factor for lingrain development, especially under limited water condition with respect to playing a significant role in nutrient and water absorption in water-limited plants4.