Aqueous Extracts of Three Herbs Allelopathically Inhibit Lettuce Germination but Promote Seedling Growth at Low Concentrations

Abstract

Allelopathy is an important process in plant communities. The effects of allelopathy on seed germination and seedling development have been extensively investigated. However, the influences of extract soaking time and concentration on the foregoing parameters are poorly understood. Here, we conducted a seed germination assay to determine the allelopathic effects of the donor herbs Achnatherum splendens (Trin.) Nevski, Artemisia frigida Willd., and Stellera chamaejasme L., from a degraded grassland ecosystem in northern China, on lettuce (Lactuca sativa L.) seed germination and early seedling growth. Extract soaking times (12 h or 24 h) did not exhibit significantly different effects on lettuce seed germination or seedling development. However, all aqueous herb extracts inhibited lettuce seed germination and root length (RI < 0) and promoted lettuce shoot length, stem length, leaf length, and leaf width (RI > 0) at both low (0.005 g mL−1) and high (0.05 g mL−1) concentrations. Moreover, A. splendens extracts increased seedling biomass (RI > 0) and synthetical allelopathic effect (SE > 0) at both concentrations. In contrast, both A. frigida and S. chamaejasme extracts had hormesis effects, which stimulate at low concentrations (RI > 0) but inhibit at high concentrations (RI < 0) on seedling biomass and synthetical allelopathic effect (SE). The results suggest that allelopathic potential may be an important mechanism driving the dominance of A. frigida and S. chamaejasme in degraded grasslands. Reseeding allelopathy-promoting species such as A. splendens may be beneficial to grassland restoration. The present study also demonstrated that seedling biomass, root and shoot length, and seed germination rate are the optimal bioindicators in allelopathy assays and could be more representative when they are combined with the results of multivariate analyses.

The Impact of Aqueous Extracts of Verbesina sphaerocephala and Verbesina fastigiata on Germination and Growth in Solanum lycopersicum and Cucumis sativus Seedlings

“…Several studies have demonstrated optimal development in seedlings in terms of agronomic variables by evaluating the inhibition and/or delay of germination. For example, Wang et al [15] revealed that the aqueous extracts of three herbs allelopathically inhibit the germination of lettuce, but promote seedling growth in low concentrations, which is similar to what was found in this study. Mira et al [46] reported the allelopathic effect of Pteridium aquilinum on the germination and growth of economically important weeds.…”

“…Various weeds and wild plants that grow and develop in cultivated fields can contain allelopathic substances that affect seed germination [30]. Various studies, i.e., [15,16,31], have indicated that most allelopathic substances, such as secondary metabolites, are synthesized through the metabolic shikimic acid and isoprene pathways. The known allelopathic substances mainly include phenols, quinones, karinas, flavonoids, terpenes, sugars, glycosides, alkaloids, and non-protein amino acids [32].…”

“…Several allelochemicals have been aqueously extracted from various botanical species and have not been classified as either germination inhibitors or retardants, but as growth promoters. For example, the aqueous extracts of three wild herbs (Achatherum splendens, Artemisia frigida, and Stellera chamaejasme) were found to allelopathically inhibit lettuce germination, but promote seedling growth when applied in low concentrations [15]. In addition, aqueous extracts of fig leaves (Ficus carica L.) were found to affect germination, but promote growth in three medicinal species (Mint, Dandelion, and Woad) [16].…”

Volatile and Non-Volatile Allelopathic Characteristics in Thermally Processed Needles of Two Conifers

“…Considering the thermal effects, the positive correlation between bioassays and HPLC results was found with the highest dose (1 mg mL −1 ) in our results. According to the other study, certain allelopathic extracts did not negatively affect seedling growth at low concentration, causing leaf extension and total biomass increase of lettuce seedlings [23]. Furthermore, it was mentioned that dose is a critical factor for exhibiting the inhibitory effects of allelochemicals in rice hull extracts [24].…”

From Soil Amendments to Controlling Autophagy: Supporting Plant Metabolism under Conditions of Water Shortage and Salinity

“…Information on stress signaling pathways [13,[275][276][277] have been completed by experiments that analyze potential targets [278,279]. Impressive and very detailed studies showed an interplay between de novo synthesis of enzymes and cell structures and degradation of these structures by autophagy [280][281][282].…”