Spatial Distribution of Oil and Biostimulation Through the Rhizosphere of Leersia hexandra in Degraded Soil

Abstract

The aim of this study was to evaluate the spatial distribution of total petroleum hydrocarbons (TPH) in rhizoplane and non-rhizosphere of Leersia hexandra, known as Japanese grass, the effect of oil on the aerial biomass of L. hexandra, the population of plant growth-regulating bacteria, and microbial respiration in rhizosphere and non-rhizospheric soil. Samples of rhizosphere and soil were collected at 14 points across a surface of 2.3 ha, layer 1 (0–15-cm depth), layer 2 (15–30 cm), and layer 3 (30–70 cm), to measure TPH (mg kg−1). The spatial distribution of TPH defined four study zones (Z): Z1: 1393, Z2: 3455, Z3: 5574, and Z4: 7544. TPH were higher in underlying layers in the four zones. Zone 2 produced the largest amount of aerial biomass; oil induced hormesis in the grass, but inhibited it at doses ≥5574. For the rhizosphere of L. hexandra, it was cut with a sterilized knife, stimulated the population of N-fixing and phosphorus solubilizing, heterotrophic bacteria, as well as microbial respiration (day 1, 14, 21, 42, and 63 after incubation) in the four zones. The population of the three groups of bacteria was more stimulated by weathered oil in rhizosphere soil, compared to non-rhizosphere soil and with control treatment, suggesting that the rhizosphere system of L. hexandra has the potential to bioestimulate beneficial microbial activity in unpolluted and polluted areas compared to non-rhizosphere soil. We recommend the use of L. hexandra to recover soils degraded by weathered oil in farms located in the Mexican humid tropics.