Barbara J. Campbell’s research while affiliated with Clemson University and other places

Rhizosphere soil microbes are increasingly recognized for their significant roles in enhancing plant resilience to abiotic stress and stimulating plant growth. Rhizobiome adapted to dry conditions can enhance drought tolerance in crops by cross-inoculation. However, changes in the rhizobiome that help in conferring drought tolerance remain poorly understood. Here, by conducting a drought-manipulating greenhouse experiment, we characterized changes in the rhizobiome of maize (Zea mays) after cross-inoculation of rhizosphere soil collected from droughtadapted Andropogon virginicus (Andropogon rhizobiome). Results showed that maize inoculated with Andropogon rhizobiome reduced oxidative damage of leaves under drought. Drought stress increased the species richness and Shannon diversity of the fungal community. Additionally, the inoculation of Andropogon rhizobiome induced a more significant increase in fungal diversity than the inoculation of organic rhizobiome. The increase of fungal diversity was positively correlated with the increased drought resistance of maize. Bacterial richness and diversity under the inoculation of Andropogon rhizobiome were negatively affected by drought stress. In addition, increased positive links in the fungal network in the Andropogon inoculation under drought conditions as compared with the ambient controls suggests more cooperation between fungal taxa to cope with drought stress. Collectively, our findings indicate that the fungal but not bacterial community diversity and network complexity stimulates drought tolerance in maize by cross-inoculation of the rhizobiome from A. virginicus. This study provides important insights that will enhance theoretical understanding and applications of plant–rhizobiome associations to promote drought resilience in agricultural crops.

The close association between bacteria and insect hosts has played an indispensable role in insect diversity and ecology. Thus, continued characterization of such insect-associated-microbial communities is imperative, especially those of saprophagous scarab beetles. The bacterial community of the digestive tract of adults and larvae of the cetoniine scarab species Cotinis nitida is characterized according to life stage, gut structure, and sex via high-throughput 16S rRNA gene amplicon sequencing. Through permutational ANOVAs of the resulting sequences, bacterial communities of the digestive system are shown to differ significantly between adults and larvae in taxon richness, evenness and relatedness. Significant bacterial community-level differences are also observed between the midgut and hindgut in adult beetles, while no significant host-sex differences are observed. The partitioning between bacterial communities in the larval digestive system is shown through significant differences in two distinct hindgut regions, the ileum and the expanded paunch, but not between the midgut and ileum portion of the hindgut region. These data further corroborate the hypothesis of strong community partitioning in the gut of members of the Scarabaeoidea, suggest hypotheses of physiological-digestive association, and also demonstrate the presence of a seemingly unusual non-scarab-associated taxon. These findings contribute to a general portrait of scarabaeoid digestive tract bacterial communities while illuminating the microbiome of a common new world cetoniine of the Gymnetini—a tribe largely neglected in scarab and beetle microbiome and symbiosis literature.

Rhizobiome confer stress tolerance to ruderal plants, yet their ability to alleviate stress in crops is widely debated, and the associated mechanisms are poorly understood. We monitored the drought tolerance of maize (Zea mays) as influenced by the cross‐inoculation of rhizobiota from a congeneric ruderal grass Andropogon virginicus (andropogon‐inoculum), and rhizobiota from organic farm maintained under mesic condition (organic‐inoculum). Across drought treatments (40% field capacity), maize that received andropogon‐inoculum produced two‐fold greater biomass. This drought tolerance translated to a similar leaf metabolomic composition as that of the well‐watered control (80% field capacity) and reduced oxidative damage, despite a lower activity of antioxidant enzymes. At a morphological‐level, drought tolerance was associated with an increase in specific root length and surface area facilitated by the homeostasis of phytohormones promoting root branching. At a proteome‐level, the drought tolerance was associated with upregulation of proteins related to glutathione metabolism and endoplasmic reticulum‐associated degradation process. Fungal taxa belonging to Ascomycota, Mortierellomycota, Archaeorhizomycetes, Dothideomycetes, and Agaricomycetes in andropogon‐inoculum were identified as potential indicators of drought tolerance. Our study provides a mechanistic understanding of the rhizobiome‐facilitated drought tolerance and demonstrates a better path to utilize plant–rhizobiome associations to enhance drought tolerance in crops.

The symbiosis of arbuscular mycorrhizal fungi (AMF) with plants, the most ancient and widespread association, exhibits phenotypes that range from mutualism to parasitism. However, we still lack an understanding of the cellular‐level mechanisms that differentiate and regulate these phenotypes. We assessed the modulation in growth parameters and root metabolome of two sorghum accessions inoculated with two AMF species (Rhizophagus irregularis, Gigaspora gigantea), alone and in a mixture under phosphorus (P) limiting conditions. Rhizophagus irregularis exhibited a mutualistic phenotype with increased P uptake and plant growth. This positive outcome was associated with a facilitatory metabolic response including higher abundance of organic acids and specialized metabolites critical to maintaining a functional symbiosis. However, G. gigantea exhibited a parasitic phenotype that led to plant growth depression and resulted in inhibitory plant metabolic responses including the higher abundance of p‐hydroxyphenylacetaldoxime with antifungal properties. These findings suggest that the differential outcome of plant–AMF symbiosis could be regulated by or reflected in changes in the root metabolome that arises from the interaction of the plant species with the specific AMF species. A mutualistic symbiotic association prevailed when the host plants were exposed to a mixture of AMF. Our results provide a metabolome‐level landscape of plant–AMF symbiosis and highlight the importance of the identity of both AMF and crop genotypes in facilitating a mutualistic AMF symbiosis.

The increase in dynamic interactions between climate and human activities threatens water security in terms of water quantity and quality. Most water security studies have focused on water quantity compared to water quality, while both are equally important and vital for maintaining a healthy ecosystem and human well-being. The first part of the paper provides a review of the potential impacts of climate-related extreme events (i.e., drought, flood, and wildfires) on different water quality indicators and the potential impact of cascading extreme events (e.g., drought-flood regimes) on dynamics of water quality behavior. In the second part of the paper, we demonstrate the cascading impact of severe drought and an extreme historical flood event (October 1-4, 2015) in South Carolina (USA) on water quality variables. The effect of drought on water quality in contrasting land-use settings is investigated. Finally, water quality data was collected over a period of time in three types of land-use settings to study the dynamics of multiple flood and drought events on microbial communities. Flooding conditions result in high levels of bacteria associated with fecal contamination, especially in the stream setting, where large differences between drought and flooding occur in the microbial communities. The results highlight the significant impact of cascading events on water quality and microbial communities. The effect of drought on water quality indicators in different land-use settings can be different, highlighting the dominant role of watershed characteristics. Overall, it is essential to develop quantitative frameworks in the context of sustainability science to quantify the interaction between climate, watershed, and anthropogenic variables that control stream water quality. This study highlights the importance of understanding the relationships between extreme events and water quality indicators as an important step to improve ecosystem health and sustainability. Finally, some remarks are made on the knowledge gaps which need to be addressed in future studies.