Exogenous hormones play an important role in plant growth regulation and stress tolerance. However, little is known about the effect of exogenous abscisic acid (ABA) on wheat seedlings under salt and alkali stresses. Here, a pot experiment of saline and alkaline stresses (0 and 100 mmol/L) in which ABA water solution (0, 50 and 100 μmol/L) was sprayed on wheat seedlings was conducted to study the alleviative effectiveness of ABA on salt and alkali stresses. After spraying ABA (50 μmol·L⁻¹), shoot biomass increased 19.0% and 26.7%, respectively. The Na⁺ content in shoots reduced from 15-fold and 61.5-fold to 10-fold and 37.3-fold in salt and alkali stresses, compared to controls. In addition, proline and organic acid synthesis in shoots also reduced significantly, but the soluble sugar content increased under alkali stress. A high concentration of ABA (100 μmol·L⁻¹) had no significant effects on biomass and ion content in wheat seedlings under both stresses. In conclusion, foliar application of ABA with moderate concentration could effectively accelerate shoot growth of salt-induced wheat seedlings by adjusting the levels of ions and organic solutes.

Hordeum jubatum is a halophyte ornamental plant wildly distributed in the Northeast of China, where the low water potential induced by various abiotic stresses is a major factor limiting plant growth and development. However, little is known about the comparative effects of salt, alkali, and drought stresses at uniform water potential on the plants. In the present study, the growth, gas exchange parameters, photosynthetic pigments, and chlorophyll fluorescence in the seedlings of H. jubatum under three low water potentials were measured. The results showed that the growth and photosynthetic parameters under these stresses were all decreased except for carotenoid (Car) with the increasing of stress concentration, and alkali stress caused the most damaging effects on the seedlings. The decreased net photosynthetic rate (Pn), stomatal conductance (Gs), and intercellular CO₂ concentrations (Ci) values under salt stress were mainly attributed to stomatal factors, while non-stomatal factors were dominate under drought and alkali stresses. The reduced chlorophyll and slightly increased Car contents occurred under these stresses, and most significant changed under alkali stress. In addition, the maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency (ΦPSII), and photochemical quenching coefficient (q_P) under the stresses were all decreased, indicating that salt, alkali, and drought stresses all increased susceptibility of PSII to photoinhibition, reduced the photosynthetic activity by the declined absorption of light for photochemistry, and increased PSII active reaction centers. Moreover, the non-photochemical quenching coefficient (NPQ) of alkali stress was different from salt and drought stresses, showing that the high pH of alkali stress caused more damaging effects on the photoprotection mechanism depending on the xanthophyll cycle. The above results suggest that the H. jubatum has stronger tolerance of salt than drought and alkali stresses, and the negative effects of alkali stress on the growth and photosynthetic performance of this species was most serious.

As important components of the photosynthetic apparatus, photosystems I (PS I) and II (PS II) are sensitive to salinity. Salt stress can destroy the PS II reaction center, disrupt electron transport from PS II to PS I, and ultimately lead to a decrease in the photosynthetic capacity of the plant. Arbuscular mycorrhizal fungi (AMF) can enhance the photosynthetic capacity of a host plant under salinity stress. However, this specific effect of AMF is not always predictable. Here, we conducted a meta-analysis including 436 independent observations to compare chlorophyll fluorescence parameters in response to AMF inoculation under salt stress. The results showed that AMF inoculation had a positive total impact on photosynthesis in the host plant. Subgroup analysis showed that annual host plants had better performance in terms of photosynthesis after inoculation. The mitigating effects of AMF on the photosynthetic rate (Pn), actual quantum yield of photochemical energy conversion in PS II (ɸPS II), and electron transfer rate (ETR) in C4 species were higher than those in C3 species. Moreover, the photosynthesis performance of monocotyledon species was better than that of dicotyledon species after AMF inoculation. The woody host plants had higher energy utilization by way of an enhanced electron transfer rate to reduce energy dissipation after AMF inoculation. Finally, the mitigating effect of AMF on plants under moderate salinity was stronger than that under high salinity. Among AMF species, Funneliformis mosseae was found to be the most effective in enhancing the photosynthesis performance of plants. For the analyzed dataset, AMF inoculation alleviated the detrimental effects of salinity on photosystem II of the host plant by improving the utilization of photons and photosynthetic electron transport, and also by reducing the susceptibility of photosystem II to photoinhibition.

Rhizosphere microorganisms are crucial for enhancing plant stress resistance. Current studies have shown that Arbuscular mycorrhizal fungi (AMF) can facilitate vegetation recovery in heavy metal-contaminated soils through interactions with rhizosphere microbiota. However, the mechanisms by which AMF influences rhizosphere microbiota and plant growth under cadmium (Cd) stress remain unclear. In this study, Lolium perenne L. was inoculated with AMF (Rhizophagus irregularis) and grown in soils supplemented with Cd (0 mg kg⁻¹, Cd0; 100 mg kg⁻¹, Cd100). Plant biomass, antioxidant enzyme activities, peroxide content, Cd uptake, and rhizosphere bacterial community composition were evaluated. AMF inoculation reduced Cd influx in aboveground tissues, enhanced nutrient availability in the rhizosphere, and mitigated Cd biotoxicity. Additionally, AMF inoculation improved the scavenging efficiency of reactive oxygen species and alleviated oxidative stress in L. perenne, thereby mitigating biomass reduction. Moreover, AMF treatment increased leaf and root biomass by 342.94% and 41.31%, respectively. Furthermore, under the same Cd concentration, AMF inoculation increased bacterial diversity (as measured by the Shannon index) and reduced bacterial enrichment (as indicated by the ACE index). AMF promoted the enrichment of certain bacterial genera (e.g., Proteobacteria and Actinobacteria) in the Cd100 group. These findings suggest that AMF regulated the composition of the rhizosphere bacterial community and promoted the growth of potentially beneficial microorganisms, thereby enhancing the resistance of L. perenne to Cd stress. Cd contamination in soil severely limits plant growth and threatens ecosystem stability, highlighting the need to understand how AMF and rhizosphere microbes can enhance Cd tolerance in L. perenne. Therefore, inoculating plants with AMF is a promising strategy for enhancing their adaptability to Cd-contaminated soils.

Ryegrass has a relatively high salt tolerance and is considered to be a promising species for both foraging and turf purposes in salt-affected soils in China. While annual ryegrass and perennial ryegrass are two different species, they have similar genomes. However, little is known about their physiological and molecular response mechanisms to salinity stress. Here, biomass, chlorophyll fluorescence, and inorganic ion and organic solute content were measured. 2-DE-based proteomic technology was then used to identify the differentially expressed proteins in the salt-treated seedlings. The results showed that salt stress reduced growth and photosynthesis in the seedlings of both species, but much more so in annual ryegrass. With increasing salinity, the Na⁺ concentration increased while the K⁺ concentration decreased in both species, and the sugars and proline increased as the primary organic solutes used to cope with osmotic stress. Additionally, proteomic analysis revealed 33 and 37 differentially expressed proteins in annual and perennial ryegrass, respectively. Most of the identified proteins were involved in carbohydrate and energy metabolism, photosynthesis, genetic information processes, amino acid metabolism, stress defense, and protein synthesis and folding. The results suggest that the two-ryegrass species had different physiological and proteomic responses. These findings can provide new insights into physiological mechanisms by which ryegrass species respond to salt stress.