Inoculation with extreme endophytes improves performance and nutritional quality in crop species grown under exoplanetary conditions

Abstract

Introduction: Technological advances have made possible long space travels and even exoplanetary colonies in the future. Nevertheless, the success of these activities depends on our ability to produce edible plants in stressful conditions such as high radiation, extreme temperatures and low oxygen levels. Since beneficial microorganisms, such as fungal endophytes from extreme environments, have helped agriculture cope with those difficulties, endophytic fungi may be a putative tool to ensure plant growth under exoplanetary conditions. Additionally, growing crops in polyculture has been shown to increase productivity and spatial efficiency, which is essential given the likely space restrictions in such conditions.

Methods: We evaluated the effect of the inoculation with a mix of two fungal endophytes from the Atacama Desert on performance (survival and biomass) and nutritional quality of three crop species (lettuce, chard and spinach) grown under exoplanetary conditions. In addition, we measured the amount of antioxidants (flavonoids and phenolics) as possible mechanisms to cope with such abiotic conditions. The exoplanetary conditions were; high UV radiation, low temperature, low water availability, and low oxygen levels. These crops were put in growing chambers in monoculture, dual culture and polyculture (the three species in the same pot) for 30 days.

Results and discussion: Our results show that inoculation with extreme endophytes improved survival by ca. 15 - 35% and biomass by ca. 30 - 35% in all crop species. The most evident increase was when grown in polyculture, except for survival in spinach, where inoculated plants had higher survival only in dual culture. Nutritional quality and the amount of the antioxidant compounds antioxidants increased in all crop species when inoculated with the endophytes. Overall, fungal endophytes isolated from extreme environments such as the Atacama Desert, the driest desert in the world, could be a key biotechnological tool for future space agriculture, helping plants cope with environmental stress. Additionally, inoculated plants should be grown in polyculture to increase crop turnover and space-use efficiency. Lastly, these results provide useful insights to face the future challenges of space-farming.

Keywords: Atacama Desert; astrobiology; crops; endophytes; extremophiles; space farming.

Figure 1

Effects of endophyte treatment (E- and E+), crop culture type (mono-culture, dual- and tri-culture) and their interaction on (A) survival and (B) biomass percentages in the three crop species, i.e., chard, lettuce and spinach. Mean crop culture types and their 95% confidence intervals (CI) are shown for chard (red), lettuce (blue) and spinach (green) treated without (pale circles) and with endophytes (filled circles). Means are derived from 150 replicate plants per treatment. Asterisks denote significant effects of endophyte treatment (E), crop culture type (C) or their interaction (E×C) as shown in Table 1 .

Figure 2

Mean effect sizes (Cohen’s f statistics) of differences in nutritional traits between endophytes-inoculated plants compared to un-inoculated plants in all crop species. Error bars depict 95% confidence intervals (CIs). A mean effect size is significantly different from zero when CIs do not overlap zero. Significant results are denoted with filled circles. Positive (or negative) effect sizes indicate that endophytes-inoculated plants have on average greater (or lesser) nutritional trait concentration than un-inoculated plants. Means are derived from 50 replicate plants per each crop species (25 ind., E+ and 25 ind., E-).

Figure 3

Effects of endophyte treatment –uninoculated (E-) vs. endophytes-inoculated (E+)– on (A) total flavonoids and (B) total phenolics in the three crop species, i.e., chard, lettuce and spinach. Mean and 95% confidence intervals (CI) are shown for E- (pale circles) and E+ (filled circles) plants of chard (red), lettuce (blue) and spinach (green). Means are derived from 50 replicate plants per each crop species (25 ind., E+ and 25 ind., E-).