About this Research Topic
There is an intrinsic need to incorporate plants and other primary producers (e.g., algae) into the life-support systems that will support human exploration beyond the boundaries of Earth. Understanding how these organisms respond and adapt to spaceflight and other extraterrestrial environments represents an exciting and critical scientific and engineering challenge. Photosynthetic organisms are keystones in the vast majority of terrestrial and aquatic ecosystems as they, in whole or in part, form the base of nearly all food webs. These organisms have enabled life on Earth and will continue to enable human survival as we continue to explore extraterrestrial environments and establish ourselves on other planetary bodies.
The challenge of creating a spaceflight environment that not only sustains human life but also allows us to be productive and thrive is a daunting task. The concept of using a combination of physical, chemical, and biological systems that are regenerative in nature is key to addressing the life-support challenges associated with long-duration human space exploration. Bioregenerative Life Support Systems (BLSSs), where resources are continuously recycled via metabolic/biological processes, would minimize the need for re-supply from Earth, while contributing significantly to the overall well-being (physical and mental) of the crews tasked with exploring and colonizing our solar system.
The spaceflight environment represents a set of environmental conditions well outside of the evolutionary experience of any terrestrial life form including plants and algae. This does not preclude survival in the spaceflight environment but it does require plants to utilize genetic resources in ways that may not otherwise be expected in normal terrestrial settings. Plant growth in space is influenced by the addition of new abiotic factors (e.g., increased cosmic radiation) and/or the removal of previously ubiquitous abiotic factors (e.g., gravity/microgravity). Gravity plays an important role in plant growth, development and orientation on Earth. Reduced levels of gravity affect many processes including gene expression, cell division, root development, vascular development, and lignification. Moreover, altered gravity dramatically influences fluid-dynamics, which has a direct impact on plant physiological processes. The interaction of microgravity with other environmental factors (i.e. temperature, light, super elevated CO2) complicates the morpho-anatomical modifications making it difficult to define a ‘typical’ response. Ionizing radiation may have different effects on plant metabolism, growth and reproduction depending on the dose and radiation quality (i.e., high or low LET – Linear Energy Transfer). The outcomes can be positive at very low doses but quite detrimental at high doses. Moreover, at the same dose, high-LET radiation is more active than low-LET radiation in inducing biological damage. The severity of the radiation-induced effects varies with species, cultivars, physiological status, and developmental stage.
Studies occurred directly in space such as parabolic flights or experiments on International Space Station (ISS) offer a great opportunity for scientific community for understanding the response of autotrophic organisms to multiple stress and its role in plant physiology. Also, Space-oriented experiments carried out on the ground provide a valuable tool to gain knowledge on plants and micro-organisms behavior in closed controlled environments. The most relevant literature, at present, shows contrasting outcomes in relation to dose, radiation quality, and species. Modifications at the anatomical, biochemical, and physiological level have been demonstrated. In terms of BLSS, it is the whole plant response that will ultimately determine the functionality of bioregenerative life-support systems, hence, studies are emerging to shed light on physiological, biochemical and molecular level effects of the integrated spaceflight environment.
The goal of this Research Topic is to assemble a current and representative cross-section of space biology research as it relates to photosynthetic autotrophic organisms, namely plants, algae, and cyanobacteria. We welcome submissions examining the influence of spaceflight and spaceflight analog environments on photosynthetic organisms, including gravity sensing, radiation tolerance mechanisms, and crop management strategies (e.g., cultivation practices/systems, lighting systems, water and nutrient delivery systems, atmospheric management including CO2, water vapour, and air flow) required to achieve sustainable bioregenerative life-support for human space exploration.
Permanent and sustainable habitation beyond the protection of the terrestrial sphere will absolutely require the [bioregenerative] services of plants and other biological systems. There has been a great deal of progress made in characterizing and understanding the response of plants and other organisms to Low Earth Orbit (LEO) spaceflight environments, yet many questions remain. If we are to send humans beyond LEO for extended periods, it is absolutely critical that we take the necessary research steps to evaluate the resiliency of biological systems and understand their responses to these new and extreme environments. As we develop a deeper understanding of the influence and response to spaceflight environments, both in LEO and beyond, we can then apply modern scientific tools to modify or adapt the biology to be better suited to carry out the functions of human life-support.
Keywords: Space, Bioregenerative Life Support Systems (BLSSs), Altered Gravity, Hydroponic, Ionizing Radiation
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