Combined addition of plant litter altered remediating effects on petroleum‐contaminated soil in Northern Shaanxi, China

Abstract

In the present study, we assessed whether the nonadditive effects of mixed litter decomposition on soil biological and chemical properties, which was usually recognized in clean soils, could be used to enhance the efficiency of petroleum‐contaminated soil necrophytoremediation. In particular, six common plant species from the petroleum production region of Northern Shaanxi, China were collected, forming nine mixture types. The single and mixed litters were used to treat petroleum‐contaminated soil with a proportion of 45 g kg−1 at 25°C and a constant humidity for 150 days. The possible nonadditive effects on the efficiency of removing contaminants and recovering the damaged soil traits caused by the mixed litter addition were then investigated. The results indicate that monospecific litter treatments significantly increased the degradation rates of petroleum contaminants, the available N and P contents, and the catalase and dehydrogenase activities by 36%–74%, 28%–455%, and 8%–102%, respectively (p < 0.05). The mixed addition of the litters from Lespedeza davurica and Artemisia scoparia or those from Agropyron cristatum and Bromus inermis caused significant synergistic effects, enhancing the overall petroleum component removal, replenishing nutrients (particularly nitrogen) or stimulating enzymatic activities (especially for sucrase, phosphatase, catalase, and urease). The observed values of the corresponding indicators following mixed litter treatment were observed to significantly increase by 12%–18%, 23%–58%, and 9%–24% (p < 0.05), relative to their predicted values, which were calculated based on the observed values from the monospecific litter treatments and the proportion of the litter in the mixture. However, other litter combinations may weaken the remediation effects of the litter addition. In general, a high content of nutrients, primary metabolites (e.g., soluble sugars and amino acids), and the potential bio‐surfactants and co‐metabolized substrates (including terpenoids and flavonoids) of mixed litters enhanced the remediation efficiency of mixed litters. Notably, an increase in the chemical diversity of mixed litter may weaken its synergistic effects on the degradation of petroleum components and the simulation of soil polyphenol oxidase activity. Our results demonstrate that appropriate litter mixing combinations can effectively enhance the efficiency of necrophytoremediation, thus providing new approaches for the more convenient and economical remediation of petroleum‐contaminated soil.

Potential effects of soil petroleum contamination on decomposition of Artemisia annua plant litter

“…The soil used for this study was artificially contaminated to simulate the effects of recent contamination on the chemical traits of plant litter. 25 To achieve this, a total of 20 quadrats measuring 1 m × 1 m were established within the uncontaminated region located on the slopes around the wells. Soil from the 0–10 cm layer was collected from each quadrat and passed through a 5 mm sieve to remove debris such as stones and plant and animal residues.…”

“…Subsequently, all contaminated and uncontaminated soil subsamples were placed in a shaded laboratory for 15 days to achieve full homogenization of the contaminated soils. 25 After 15 days, the actual petroleum concentrations in the lightly, moderately, and heavily contaminated soils were measured as 14.52 ± 0.26, 29.06 ± 0.63, and 44.97 ± 0.19 g kg −1 , respectively. These values showed no significant differences from the designed concentrations ( P > 0.05).…”

“…Their N and P contents were determined through phenol-blue colorimetry and vanadium-molybdenum yellow colorimetry after the samples were digested with sulfuric acid and 30% hydrogen peroxide. 25 The lignin and cellulose contents of undecomposed litter were determined using kits purchased from Solarbio Science & Technology Co., Ltd (Beijing, China). The total petroleum hydrocarbon (TPH) content was determined using the Soxhlet extractor method.…”

“…However, petroleum contamination and its remediation processes typically deplete soil nitrogen and phosphorus levels, compounded by the already limited background nutrient content in local soil. 2,19,25 Consequently, the long-term growth of remedial plants is oen constrained by nutrient availability. Therefore, the impact of soil petroleum contamination on the chemical properties of litter, inhibiting decomposition and nutrient release, directly inuences the ability of these plants to establish stable communities in contaminated regions and fulll their ecological roles.…”