Alleviation of Detrimental Effects of Salt Stress on Date Palm (Phoenix dactylifera L.) by the Application of Arbuscular Mycorrhizal Fungi and/or Compost

Abstract

The date palm is a commercially important woody crop and is a good target plant for improving agricultural yields in extreme environments. However, salinity has been the primary abiotic stress complicating its cultivation and damaging its production worldwide. This study investigated the effect of alleviating salt stress on date palm growth and development by using arbuscular mycorrhizal fungi (AMF) and/or compost. The experiment was arranged in a completely randomized design with eight treatments. The treatments comprised control without inoculation or amendment and application of compost (made from green waste) and AMF (an autochthonous consortium) individually or in combination under non-saline (0 mM NaCl) or saline (240 mM NaCl) conditions. Growth, physiological characteristics, nutrient uptake, chlorophyll content, oxidative stress markers, and antioxidant enzyme activities were assessed. Salt stress increased sodium (Na +) and chlorine (Cl −) content, lipid peroxidation and proline, soluble sugar, and H 2 O 2 content. However, it reduced growth parameters, AMF colonization, leaf water potential, nitrogen (N), phosphorus (P), potassium (K +), calcium (Ca 2+), and chlorophyll content. The application of AMF and compost separately or in combination mitigated the deleterious effects induced by salinity. AMF inoculation contributed to plant salt tolerance through strategies such as increased nutrient uptake (particularly P and Ca 2+), chlorophyll content, relative water content, stomatal conductance, antioxidant enzymatic activities (superoxide dismutase, ascorbate peroxidase, catalase) and by decreasing lipid peroxidation and H 2 O 2 content. Plants grown in soil amended with compost under salt stress showed an improvement particularly in K + and proline content and a decrease in H 2 O 2 concentration compared to controls under the saline condition. In the presence of NaCl stress, the dual application of the compost and AMF consortium maximized plant growth, stomatal conductance, leaf water potential, all antioxidant enzyme activities and P, K + , N, and Ca 2+ uptake as well as proline and soluble sugar content. However, Ait-El-Mokhtar et al. Mycorrhiza-and Compost-Mediated Salinity Tolerance it reduced Na + and Cl − uptake and oxidative stress marker content. In conclusion, our study suggests that the application of AMF with compost has the potential to improve the tolerance of date palm seedlings to salt stress more than AMF or compost applied separately.

Arbuscular Mycorrhizal Fungi Improve Tolerance of the Medicinal Plant Eclipta prostrata (L.) and Induce Major Changes in Polyphenol Profiles Under Salt Stresses

“…This may suggest that at the first stage of plant growth, POD and CAT were two major antioxidative enzymes in mycorrhizal E. prostrata plants to alleviate oxidative stress caused by moderate saline conditions. The present results concur with those in cucumber plants ( Hashem et al, 2018 ) and date palm plants ( Ait-El-Mokhtar et al, 2020 ). By contrast, at the later stage, fungal symbiosis did not change the activity of these enzymes in response to salt stresses.…”

“…Although AMF have been shown to improve plant performance under salinity in many plant species ( Santander et al, 2019 ; Ait-El-Mokhtar et al, 2020 ; Amanifar and Toghranegar, 2020 ), responses of mycorrhizal E. prostrata plants to salinity, especially in terms of bioactive compounds, have not been addressed. In the present work, mycorrhizal colonization rate was markedly reduced after 4 weeks of plant growth due to the high saline level (200 mM NaCl), but not at the later stage of plant growth ( Figure 2 ).…”

“…Plant biomass is the most prominent and direct attribute showing symbiosis-mediated plant performance under salt stress. AM inoculation has been reported to enhance the growth characteristics of several plants subjected to saline conditions, such as lettuce ( Santander et al, 2019 ), date palm ( Phoenix dactylifera L.) ( Ait-El-Mokhtar et al, 2020 ), and the medicinal plant V. officinalis (L.) ( Amanifar and Toghranegar, 2020 ). These findings support that the beneficial effects of AM application on the growth of host plants under salinity are consistent with our observation (increased fresh shoot weight, leaf number, and leaf area) under moderate salinity.…”

Effect of co-inoculation with arbuscular mycorrhizal fungi and phosphate solubilizing fungi on nutrient uptake and photosynthesis of beach palm under salt stress environment

“…Colonization of plant roots and soils by AMF could promote plant nutrient acquisition by increasing available phosphorus (P), hydrolyzable nitrogen (N), organic matter content, and several enzyme activities in soil 10 , 11 . The application of mycorrhizal inoculants could also improve the photosynthesis of plants by increasing Chl content 5 , transpiration rate ( E ), and stomatal conductance ( G s ) and reducing Na + and Cl − uptake 5 , 12 – 14 in host plants under salt stress. Inoculation of plants with phosphate-solubilizing fungus (PSF), Apophysomyces spartima , is also applied for saline soil restoration because it can increase P availability in soils fertilized with rock phosphates 15 .…”

“…It is well known that the uptake of mineral nutrients by underground roots and the efficiency of photosynthesis of aboveground leaves are "source" forces for plant growth. Higher concentrations of ions (Na + , Cl − , SO 4 2− ) in saline soils accumulate in plant cells and inhibit nutrient (e.g., nitrogen, phosphorus, and potassium) uptake 4 and photosynthesis 5 . In fact, salinity was found to inhibit specific enzymes involved in the synthesis of photosynthetic pigments, resulting in the decrease of chlorophyll content 6 .…”