Sampling Root-Associated Microbiome Communities of Maize (Zea mays).

The soil microbiome of maize shapes its fitness, sustainability, and productivity. Accurately sampling maize's belowground microbial communities is important for identifying and characterizing these functions. Here, we describe a protocol to sample the maize rhizosphere (including the rhizoplane and endorhizosphere) and root zone (still influential but further from the root) in a form suitable for downstream analyses like culturing and DNA extractions. Although this protocol is written with Zea mays as the focus, these methods can generally be applied to any plant with similar fibrous root systems.

Sampling and Analysis of the Maize Microbiome.

Maize is an important plant for both global food security and genetics research. As the importance of microorganisms to plant health is becoming clearer, there is a growing interest in understanding the relationship between maize and its associated microbiome; i.e., the collection of microorganisms living on, around, and inside the plant. The ultimate goal of this research is to use these microbial communities to support more robust and sustainable maize production. Here, we provide an overview of recent progress in the field of maize microbiome research. We discuss the major microbiome compartments (rhizosphere, phyllosphere, and endosphere) and known functions of the microbiome. We also review the methods currently available to study the maize microbiome and its functions, and discuss how to carry out maize microbiome experiments, including both a general workflow (suitable for most microbiome analyses) and maize-specific experimental considerations.

Manipulating the Maize (Zea mays) Microbiome.

Maize (Zea mays) is a multifaceted cereal grass used globally for nutrition, animal feed, food processing, and biofuels, and a model system in genetics research. Studying the maize microbiome sometimes requires its manipulation to identify the contributions of specific taxa and ecological traits (i.e., diversity, richness, network structure) to maize growth and physiology. Due to regulatory constraints on applying engineered microorganisms in field settings, greenhouse-based experimentation is often the first step for understanding the contribution of root-associated microbiota-whether natural or engineered-to plant phenotypes. In this protocol, we describe methods to inoculate maize with a specific microbiome as a tool for understanding the microbiota's influence on its host plant. The protocol involves removal of the native seed microbiome followed by inoculation of new microorganisms; separate protocols are provided for inoculations from pure culture, from soil slurry, or by mixing in live soil. These protocols cover the most common methods for manipulating the maize microbiome in soil-grown plants in the greenhouse. The methods outlined will ultimately result in rhizosphere microbial assemblages with varying degrees of microbial diversity, ranging from low diversity (individual strain and synthetic community [SynCom] inoculation) to high diversity (percent live inoculation), with the slurry inoculation method representing an "intermediate diversity" treatment.

Education in the Anthropocene: assessing planetary health science standards in the USA.

The environmental crises defining the Anthropocene demand ubiquitous mitigation efforts, met with collective support. Yet, disengagement and disbelief surrounding planetary health threats are pervasive, especially in the USA. This scepticism may be influenced by inadequate education addressing the scope and urgency of the planetary health crisis. We analysed current K-12 science standards related to planetary health throughout the USA, assessing their quality and potential predictors of variation. While planetary health education varies widely across the USA with respect to the presence and depth of terms, most science standards neglected to convey these concepts with a sense of urgency. Furthermore, state/territory dominant political party and primary gross domestic product (GDP) contributor were each predictive of the quality of planetary health education. We propose that a nation-wide science standard could fully address the urgency of the planetary health crisis and prevent political bias from influencing the breadth and depth of concepts covered.

Maize germplasm chronosequence shows crop breeding history impacts recruitment of the rhizosphere microbiome.

Recruitment of microorganisms to the rhizosphere varies among plant genotypes, yet an understanding of whether the microbiome can be altered by selection on the host is relatively unknown. Here, we performed a common garden study to characterize recruitment of rhizosphere microbiome, functional groups, for 20 expired Plant Variety Protection Act maize lines spanning a chronosequence of development from 1949 to 1986. This time frame brackets a series of agronomic innovations, namely improvements in breeding and the application of synthetic nitrogenous fertilizers, technologies that define modern industrial agriculture. We assessed the impact of chronological agronomic improvements on recruitment of the rhizosphere microbiome in maize, with emphasis on nitrogen cycling functional groups. In addition, we quantified the microbial genes involved in nitrogen cycling and predicted functional pathways present in the microbiome of each genotype. Both genetic relatednesses of host plant and decade of germplasm development were significant factors in the recruitment of the rhizosphere microbiome. More recently developed germplasm recruited fewer microbial taxa with the genetic capability for sustainable nitrogen provisioning and larger populations of microorganisms that contribute to N losses. This study indicates that the development of high-yielding varieties and agronomic management approaches of industrial agriculture inadvertently modified interactions between maize and its microbiome.