The use of plant growth promoting rhizobacteria (PGPRs) to improve crop growth under salt stress is gaining attention in recent years. In this study, we evaluated the potential of Bacillus amyloliquefaciens strain Q1 to mitigate salt stress in barley. Barley seedlings were inoculated without (-) or with (+) Q1 and then subjected to four salt levels (0-320 mM) to assess the changes in plant growth, photosynthetic attributes, ion homeostasis, and antioxidant capacity. Our results revealed that the slight salt stress (80 mM) caused little damage to plant growth and physiological processes of barley seedlings, indicating the potential of barley for crop production in saline soils equal to or less than this salt level. However, the moderate (160 mM)- or severe (320 mM)-level salt stress considerably reduced the plant growth of barley seedlings, because of the inhibition of photosynthetic capacity and disruption of Na+/K+ homeostasis. The inoculation with Q1 notably ameliorated these detrimental effects of salt stress, and its efficacy was more predominant at the severe salt level. Moreover, Q1 significantly enhanced the activities of antioxidant enzymes in barley at the severe salt level, but not at the slight or moderate salt level. Taken together, it is concluded that Q1 has limited promoting effect on barley under the normal growth condition, whereas it is capable to help barley maintain much better growth and performance under salt stress, especially at the severe level. Our study has expanded the list of PGPR resources for sustainable utilization of saline land.

Waterlogging increasingly challenges crop production, affecting 10% of global arable land, necessitating the development of pragmatic strategies for mitigating the downside risk of yield penalty. Here, we conducted experiments under controlled (tank) and field conditions to evaluate the efficacy of nitrogenous fertiliser in alleviating waterlogging stress. Without intervention, we found that waterlogging reduced grain yields, spike numbers and shoot biomass, but had a de minimus impact on grain number per spike and increased grain weight. Soil fertiliser mitigated waterlogging damage, enhancing yields via increased spike numbers, with crop recovery post-waterlogging catalysed via improved tiller numbers, plant height and canopy greenness. Foliar nitrogen spray has little impact on crop recovery, possibly due to stomatal closure, while modest urea application during and after waterlogging yielded similar results to greater N application at the end of waterlogging. Waterlogging-tolerant genotypes (P-17 and P-52) showed superior growth and recovery during and after waterlogging compared to the waterlogging-sensitive genotypes (Planet and P-79). A comparison of fertiliser timing revealed that field fertilizer treatment two (F2: 90 kgha(-1) at 28 DWL, 45 kgha(-1) at sowing and 45 kgha(-1) at 30 DR) yielded the highest and fertilizer treatment three (F3: 45 kgha(-1) at sowing and 45 kgha(-1) at 30 DR) recovered the lowest yield and spike number, while fertilizer treatment one (F1: 45 kgha(-1) at 28 DWL, 45 kgha(-1) at 0 DR, 45 kgha(-1) at sowing and 45 kgha(-1) at 30 DR) and four (F4: 90 kgha(-1) at 0 DR, 45 kgha(-1 )at sowing and 45 kgha(-1 )at 30 DR) had the highest shoot biomass in the field. Treatment five (T5: 180 kgha-1 at 0 DR, 30 kgha(-1) at sowing and 90 kgha(-1) at 30 DR) presented the most favourable results in the tank. Our results provide rigorous evidence that long periods of waterlogging caused significant yield penalty, mainly due to decreased spike numbers. We contend that increasing fertiliser rates during waterlogging up to 90 kgha(-1) can provoke crop growth and mitigate waterlogging-induced grain yield losses, and is more beneficial than applying nitrogen post-waterlogging.

The occurrence of drought in soils, particularly in those contaminated by metals, poses a current threat to crops, as these factors can interact and induce unique stress responses. Therefore, this study mainly focused on understanding the crosstalk between drought and copper (Cu) stress in the physiology of the barley (Hordeum vulgare L.) plant. Using a bifactorial experimental design, seedlings were grown in a natural soil under the following treatments: plants continuously irrigated in uncontaminated soil for 14 days (control); plants continuously irrigated in Cu-contaminated soil (115 mg Cu kg-1) for 14 days (Cu); plants only irrigated during the initials 7 days of growth in uncontaminated soil (drought); plants co-exposed to Cu and drought (combined). After 14 days of growth, the results revealed that drought prevented Cu bioaccumulation in barley roots, which were still severely affected by the metal, both individually and in combination with the water deficit. Furthermore, individual and combined exposure to these stressors resulted in impaired photosynthetic performance in barley plants. Despite the increased activation of enzymatic and non-enzymatic antioxidant defence mechanisms, particularly in the green organs, the plants co-exposed to both stress factors still showed higher oxidative damage, severely impacting biomass production.