Plant growth-promoting bacteria (PGPB) can mitigate the effect of abiotic stresses on plant growth and development; however, the degree of plant response is host-specific. The present study aimed to assess the growth-promoting effect of Herbaspirillum (AP21, AP02), Azospirillum (D7), and Pseudomonas (N7) strains (single and co-inoculated) in perennial ryegrass plants subjected to drought. The plants were grown under controlled conditions and subjected to water deficit for 10 days. A significant increase of approximately 30% in dry biomass production was observed using three co-inoculation combinations (p < 0.01). Genomic analysis enabled the detection of representative genes associated with plant colonization and growth promotion. In vitro tests revealed that all the strains could produce indolic compounds and exopolysaccharides and suggested that they could promote plant growth via volatile organic compounds. Co-inoculations mostly decreased the in vitro-tested growth-promoting traits; however, the co-inoculation of Herbaspirillum sp. AP21 and Azospirillum brasilense D7 resulted in the highest indolic compound production (p < 0.05). Although the Azospirillum strain showed the highest potential in the in vitro and in silico tests, the plants responded better when PGPB were co-inoculated, demonstrating the importance of integrating in silico, in vitro, and in vivo assessment results when selecting PGPB to mitigate drought stress.

Semi-arid environments characterized by low rainfall are subject to soil desertification processes. These environments have heterogeneous landscapes with patches of vegetation known as resource islands that are generated by nurse species that delay the desertification process because they increase the availability of water and nutrients in the soil. The study aimed to characterize some foliar physiological, biochemical, and anatomical traits of three nurse tree species that form resource islands in the semi-arid environment of La Guajira, Colombia, i.e., Haematoxylum brasiletto, Pithecellobium dulce, and Pereskia guamacho. The results showed that H. brasiletto and P. dulce have sclerophyllous strategies, are thin (0.2 and 0.23 mm, respectively), and have a high leaf dry matter content (364.8 and 437.47 mg/g). Moreover, both species have a high photochemical performance, reaching Fv/Fm values of 0.84 and 0.82 and PI_ABS values of 5.84 and 4.42, respectively. These results agree with the OJIP curves and JIP parameters. Both species had a compact leaf with a similar dorsiventral mesophyll. On the other hand, P. guamacho has a typical succulent, equifacial leaf with a 97.78% relative water content and 0.81 mm thickness. This species had the lowest Fv/Fm (0.73) and PI_ABS (1.16) values and OJIP curve but had the highest energy dissipation value (DIo/RC).

The world is experiencing a rise in global temperatures as a result of climate change. Higher temperatures along with more frequent heat waves negatively impact physiological levels and ultimately lead to plant death. Although woody species have different strategies to regulate leaf temperature, the relative importance of structural and anatomical traits in leaf temperature regulation remains unclear. We evaluated the variation in thermal tolerance (T₅₀ and T_crit) among 17 woody species in an Andean Tropical Montane Forest in Colombia. We explored how 18 leaf structural and anatomical traits can explain the variation in thermal tolerance. Our findings revealed high variability in thermal tolerance, structural, and anatomical leaf traits among species. Thick layers of upper cuticle, epidermis, and hypodermis increased T₅₀. However, increases in T_crit were only associated with upper hypodermis thickness. Higher stomatal index, a trait related to increased stomatal conductance and leaf transpiration, increased T₅₀, while traits associated with leaf water transport did not correlate with temperature tolerance. Our results highlight the contrasting influence of leaf tissues on leaf tolerance and the diverse strategies plants employ to cope with high temperatures. These findings hold significant implications for the climate‐smart restoration of Andean Tropical Montane forests. Read the free Plain Language Summary for this article on the Journal blog.

Perennial ryegrass is a forage commonly used in temperate regions for livestock feeding; however, its yield is affected by reduced biomass production under water deficit. In a previous study, three co-inoculations of beneficial bacteria were selected based on their ability to promote plant growth under reduced water availability. The aim of this work was to elucidate some mechanisms by which the selected bacteria can help improve the response of perennial ryegrass to water deficit. Ryegrass plants were inoculated with each of the co-inoculations (Herbaspirillum sp. AP02–Herbaspirillum sp. AP21; Herbaspirillum sp. AP02–Pseudomonas sp. N7; Herbaspirillum sp. AP21–Azospirillum brasilense D7) and subjected to water deficit for 10 days. Physiological and biochemical measurements were taken 10 days after stress and shortly after rehydration. The results showed that bacteria had a positive effect on shoot biomass production, dissipation of excess energy, and proline and chlorophyll pigments during the days of water deficit (p < 0.05). The leaf water status of the inoculated plants was 12% higher than that of the uninoculated control after rehydration. Two Herbaspirillum strains showed greater potential for use as biofertilizers that help ameliorate the effects of water deficit.