Drought stress is a prevalent abiotic stress that adversely affects multiple physiological processes in plants, especially their photosynthetic capacity. Application of plant growth–promoting rhizobacteria (PGPR) has been considered as an eco-friendly strategy to ameliorate the deleterious effects of drought stress on plants. The present study was carried out to investigate the effects of Bacillus amyloliquefaciens QST713 on plant growth, leaf relative water content (RWC), photosynthesis processes, photosynthetic pigment content and antioxidant enzyme activities in two alfalfa varieties, Galalxie Max (drought-tolerant) and Saidi 7 (drought-sensitive) under drought conditions. The results showed that drought stress significantly declined plant biomass production, RWC, photosynthetic pigment content (Chl a, Chl b and carotenoids) and photosynthetic gas exchange parameters (transpiration rate (Tr), stomatal conductance (Gs) and intercellular CO2 concentration (Ci)), whereas it enhanced the enzymatic activity of peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) in both cultivars. In contrast, the inoculation of the bacillus strain QST713 was more effective on plant growth, showing higher plant biomass production compared to the non-inoculated plants under drought stress. Moreover, the application of QST713 significantly promoted the content of RWC, the accumulation of chlorophyll content and the activities of antioxidant enzymes as well as enhanced the photosynthetic capacity of alfalfa seedlings under drought stress. These results suggest that QST713 could be considered as a promising bio-inoculant for plants exposed to environmental stresses.

High-temperature stress was one of the biggest threats to cool-season turfgrass, hence breeding new varieties adapted to high temperature was the fundamental way to improve the turf quality. This study was designed to determine the changes in contents of malonaldehyde (MDA), soluble sugar, soluble protein and proline, and activities of superoxide dismutase (SOD) and catalase (CAT) in different accessions of wild Kentucky bluegrass (Poa pratensis), which was collected from 13 areas of Shanxi province and subjected to 0, 5, 10, 15, 20 and 25 days of high-temperature stress, to evaluate the adaptability of different accessions of Kentucky bluegrass to high temperature stress. The results showed that the contents of soluble sugar, proline and MDA enhanced in all accessions of Kentucky bluegrass with the increase of hightemperature stress, the soluble protein contents of all accessions of Kentucky bluegrass declined under 0 to 10 days of high-temperature stress, and then increased with the increase of high-temperature stress. Inversely, the SOD and CAT activities of all Kentucky bluegrass augmented under 0 to 10 or 15 days of hightemperature stress, but they all declined with the continuous increase of high-temperature stress. The changes in osmotic and antioxidant protective system were very different in response to high-temperature stress in different accessions of Kentucky bluegrass, and the accessions of 'Qinshui' and 'Hunyuan' had the highest resistance to high-temperature stress, hence they could be used to breed new varieties that are resistant to high-temperature stress.