Drought stimulates root exudation of organic nitrogen in cotton (Gossypium hirsutem)

Aeroponic Technology for Accelerated Weathering of Extraterrestrial Regolith to Extract Plant Essential Nutrients and Generate Arable Soils

Advancements in off-world food and fiber production should seek to utilize regolith as a source of nutrients and prepare it for use as a solid plant growth substrate. Towards this goal, aeroponic biowaste streams containing both inorganic nutrients and root system efflux from plants provide an opportunity for accelerated weathering and enhancement of extraterrestrial soils. To test this hypothesis, an aeroponic system was built that contained Martian simulant (Mars Mojave Simulant-2; MMS-2), inert sand, and a no-filter control to evaluate the in-line filters for simultaneous mineral weathering and recycling of biowastes from wheat. The growth performance of wheat in aeroponics was highly productive across all treatments. After inundation with biowastes from the aeroponic system growing wheat for 40 days, MMS-2 sorbed P and K and released Al, B, Ca, Fe, Mn, Na, and S into the nutrient solution. Generated plant biowaste was mixed into MMS-2 and sand treatments, which increased the extractable Fe, K, Mg, P, and S in MMS-2. Substrate chemical properties were quantified (e.g., total C and N, total and extractable elements, pH, EC, particle size, and P species). Augmentation of MMS-2 with aeroponic biowastes followed by amendment with plant residue greatly improved wheat growth compared with the unmodified MMS-2, which resulted in plant death. This technology expands lunar/Martian base agriculture by offering a means to acquire nutrients from weathered regolith while simultaneously improving the fertility of extraterrestrial soils.

Aeroponic approach for nondestructive root exudate collection and simulation of variable water stress trialed on cotton (Gossypium hirsutum)

Analyzing root exudates during drought poses a serious challenge; sampling root exudates in soil is destructive to roots and leads to biased molecular analysis, along with microbial decomposition and exudate sorption to soil components. Hydroponic approaches are useful to overcome these problems but lack the utility to induce drought. Nondestructive sampling techniques are thus needed to analyze root exudates from the same plants over time in combination with highly controlled variable water/nutrient stress. The proposed aeroponic approach demonstrated that cotton could be grown to maturity in the aeroponic system, then a progressive drought treatment applied while simultaneously collecting root exudates from the same plants over time. Treatments of varying irrigation rates consisted of well-watered cotton (control) that was compared to cotton given progressive water stress (drought) and subsequent drought recovery for two weeks. Plants were entering flowering as drought treatment was applied. Nondestructive morphological measurements of plant productivity were made. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was employed to analyze the molecular profile of exudates, whereas gas chromatography-mass spectroscopy (GC-MS) was used to quantify abscisic acid (ABA). Plant development was highly responsive to reduced irrigation intervals with decreased canopy height, number of green leaves, biomass, and water content. As revealed by FT-ICR MS, the complexity and connectivity of unique biochemical transformation networks in response to drought was greatest at 9 days after treatment, where severe visual symptoms were observed. Overall, the aeroponic approach is a promising technology to simulate drought while sampling root exudates nondestructively, advancing root system research and plant-stress response mechanisms.