Influence of Soil Moisture on Bioaccumulation, Growth, and Recruitment ofFolsomia candidaExposed to Phenanthrene-Polluted Soil

Abstract

Climate change has resulted in an increased occurrence of summer droughts in large parts of the world. Low soil moisture has marked impacts on the physiology of soil invertebrates and lowers degradation rates of organic contaminants in soil. Polycyclic aromatic hydrocarbons (PAHs) are hydrophobic contaminants that readily accumulate in the lipids of soil organisms. Here, we exposed springtails (Collembola, small soil living arthropods) to phenanthrene (a common PAH) in combination with a range of soil water contents to investigate the combined effects of these factors on the bioaccumulation, survival, recruitment, and body growth in a full factorial experiment. The results showed that phenanthrene up to 60 mg/ kg dry soil had moderate effects on survival (<20%), whereas dry soil (4% soil water content) caused approximately 60% mortality. The bioaccumulation of phenanthrene increased almost 3-fold when soil water content decreased from 22 to 4%. We observed a joint effect of low soil water content and phenanthrene on recruitment, suggesting a synergistic interaction. The recruitment EC50 values of phenanthrene decreased from approximately 40 mg/kg dry soil at 22% soil water content to approximately 10 mg/kg dry soil at 12% soil water content. Our results show that the effects of phenanthrene are more pronounced in dry soil partly because bioaccumulation is enhanced when soils become dry.

Low soil Moisture Slows Uptake and Elimination Rates of Phenanthrene in Springtails

“…Barker, HPLC quality) using 180 mL kg − 1 dry soil. The solution and dry soil were thoroughly mixed to obtain a sublethal phenanthrene concentration of 40 mg kg − 1 dry soil (Wang et al 2023 ). The spiked soil was left overnight under a fume hood to allow the acetone to evaporate.…”

“…To examine phenanthrene concentrations in springtails over time, ten animals were added to 150 mL jars containing 30 g spiked soil as previously described (Wang et al 2023 ). In total, 60 jars were set up for each soil water content (12 sampling times, 5 replicates for each sampling time).…”

“…Since soil water content influences the springtails’ body water content (Supplementary Fig. S2) we had to estimate the internal concentration of phenanthrene on a dry weight basis as described by Wang et al ( 2023 ) using the linear relationship between exposure time and the water content of springtails exposed to noncontaminated soil (Supplementary Fig. S2) to transform the fresh weight of phenanthrene-exposed springtails to dry weight and calculate an internal concentration of phenanthrene on a dry weight basis.…”

“…Finally, we expected that the detoxification system could be induced and enhanced during the exposure period and therefore hypothesized that (3) the elimination rate increased over time. While the previous study by Wang et al ( 2023 ) was focused on the interactive effects of phenanthrene and soil moisture on the growth and reproduction of F. candida it did not provide any mechanistic understanding of the toxicokinetic aspects in these interactions. With the present study, we aim to provide this understanding.…”

“…For example, a full-factorial 28-day mesocosm experiment showed that the EC50 for recruitment of springtails was reduced from 40 to 10 mg phenanthrene kg − 1 dry soil with decreasing soil water content from 22 to 12% of dry weight (equivalent to soil water potentials of -2 and − 15 kPa, respectively). However, the seemingly higher effect in dry soil was related to higher bioaccumulation in dry soil (Wang et al 2023 ). In addition, exposure to dry soil resulted in low body water contents which is likely physiologically challenging (Bayley and Holmstrup 1999 ; Wang et al 2022 ) and may decrease the detoxification capacity of springtails.…”