Enhancement of plant drought stress tolerance by plant growth-promoting rhizobacteria (PGPR) has been increasingly documented in the literature. However, most studies to date have focused on PGPR-root/plant interactions; very little is known about PGPR's role in mediating physiochemical and hydrological changes in the rhizospheric soil that may impact plant drought stress tolerance. Our study aimed to advance mechanistic understanding of PGPR-mediated biophysical changes in the rhizospheric soil that may contribute to plant drought stress tolerance in addition to plant responses. We measured soil water retention characteristics, hydraulic conductivity, and water evaporation in soils with various textures (i.e., pure sand, sandy soil, and clay) as influenced by a representative PGPR (Bacillus subtilis strain UD1022) using the HYPROP system. We found that all PGPR-treated soils held more water and had reduced hydraulic conductivity and accumulative evaporation, compared to their corresponding controls. We discuss three mechanisms, due to B. subtilis incubation or production of extracellular polymeric substances (EPS), that are potentially responsible for the changes in hydraulic properties and soil evaporation: (i) EPS have a large water holding capacity; (ii) EPS alter soil matrix structure and connectivity of pore space; (iii) EPS modify the physicochemical properties of water (surface tension and viscosity). These results clearly demonstrate PGPR's ability to increase water availability to plants by slowing down evaporation and by increasing the time available for plants to make metabolic adjustments to drought stress.Plain Language Summary PGPR is a group of beneficial bacteria known to improve plant growth by, e.g., reducing pathogenic infection and/or promoting drought/salt tolerance. Despite the important role PGPR could potentially play in reducing drought stress to plants, we lack a complete understanding on the mechanisms through which PGPR mediate plant tolerance to drought. This study aimed to advance mechanistic understanding of PGPR-mediated biophysical changes in soil through microbe-soil interactions, to complement better understanding gained from previous studies that focused on microbe-plant interactions. Through laboratory measurements and imaging of water retention in soil, we show that a representative PGPR (B. subtilis UD1022) can increase soil water retention and reduce soil water evaporation. This effect is likely caused by the PGPR's ability to produce extracellular polymeric substances, which have high water holding capacity and can induce changes in soil physical properties. These changes lead to slower evaporation from soil, which can make more water available to plants as well as increase the time available for plants to make metabolic adjustments to drought stress. Our results provide scientific support to recent efforts in promoting application of rhizobacteria isolates as ''underground resource'' to contribute to solving globally challenging issues, e.g., water resource shortage and ...

Flexible polymers show high potential applications in rechargeable lithium–sulfur (Li–S) batteries for their capability of confining sulfur diffusion and tolerance to large volume expansion during lithiation. Herein, sulfur is copolymerized with 3-butylthiophene via radical polymerization by heating the mixture of both components at controlled temperatures. Further capping of the thus-synthesized copolymer CP­(S3BT) with highly conductive PEDOT:PSS thin film substantially enhances the electrical conductivity. With the resulting polymer hybrids as the cathode material, a Li–S battery is constructed which shows an initial discharge capacity of 1362 mA h g–1 at 0.1 C and a reversible capacity of 631 mA h g–1 even at 5 C. Moreover, the polymer cathode exhibits a high capacity of 682 mA h g–1 after 500 charge–discharge cycles at 1 C with 99.947% retention per cycle. The remarkable performance is attributed to the synergetic effects of (i) high conductivity resulting from both the conducting blocks of poly­(3-butylthiophene) (P3BT) and PEDOT:PSS capping layer, (ii) physical confinement of polysulfides by P3BT segments and PEDOT:PSS capping layers, and (iii) chemical confinement resulting from the high density of chemical bonds between sulfur and 3-butylthiophene. The results may offer a new paradigm in the development of efficient and stable polymer cathodes for high performance Li–S batteries.

Low electrical conductivity and a lack of chemical confinement are two major factors that limit the rate performances and cycling stabilities of cathode materials in lithium-sulfur (Li-S) batteries. Herein, sulfur is copolymerized with poly(m-aminothiophenol) (PMAT) nanoplates through inverse vulcanization to form the highly crosslinked copolymer cp(S-PMAT) in which approximately 80 wt % of the feed sulfur is bonded chemically to the thiol groups of PMAT. A cp(S-PMAT)/C-based cathode exhibits a high discharge capacity of 1240 mAh g at 0.1 C and remarkable rate capacities of 880 mAh g at 1 C and 600 mAh g at 5 C. Moreover, it can retain a capacity of 495 mAh g after 1000 deep discharge-charge cycles at 2 C; this corresponds to a retention of 66.9 % and a decay rate of only 0.040 % per cycle. Such a remarkable rate performance is attributed to the highly conductive pathways of PMAT nanoplates, and the excellent cycling stability is ascribed mainly to the chemical confinement of sulfur through a large number of stable covalent bonds between sulfur and the thiol groups of PMAT. The results suggest that this strategy is a viable paradigm for the design and engineering of conducting polymers with reactive functional groups as effective electrode materials for high-performance Li-S batteries.

From pyrolysis of polypyrrole nanosheets containing volatilizable FeCl3 derivatives, facilely prepared via an interfacially confined polymerization method, a honeycomb-like porous carbon catalyst with efficient ORR activity and superb performance in a Zn–air battery prototype was obtained.