Allelochemicals-based expansion of Elsholtzia densa Benth. hindering plants’defense function: case study of Hordeum vulgare L.

Abstract Background The root extracellular trap (RET) comprising root border cells (RBCs) and their secretions are plants' first line of defense to resist external stress. Since soil microorganisms are closely related to nutrient circulation, this study chooses a poisonous weed Elsholtzia densa Benth. (E. densa) in alpine meadows on the Qinghai-Tibet Plateau (QTP) to explore the mechanism of its rapid expansion. Methods Bioassays and pure agar suspension air culture methods are used to determine the effects of the decomposing substances of E. densa on the RBCs characteristics of the plateau crop highland barley (Hordeum vulgare L.), soil nutrients, soil enzyme activities, and soil bacteria, using microscopic techniques and biochemical analysis techniques.Results The decomposing allelopathic effect of the E. densa mainly occurs in the early stage of decomposing, with its decomposing solution thickening the RBC’s mucilage layer and decreasing the RBC’s activity and even apoptosis. The decomposed product of the E. densa changes the diversity of the soil bacterial and species composition, affects soil nutrient content, and increases the activities of various extracellular enzymes.Conclusions During the expansion, the E. densa releases allelochemicals to its surroundings interfering with the surrounding plants' defense function and directly inhibiting their growth. At the same time, the stubble's decomposition changes soil microbial activities, enriches the soil nutrients, and forms a self-interested soil environment. Eventually, the E. densa gains an edge over the competition.