Exploring the Structure and Substance Metabolism of a Medicago sativa L. Stem Base.

The stem base of alfalfa is a critical part for its overwintering, regeneration, and yield. To better understand the specificity and importance of the stem base, we analyzed the structure, metabolic substances, and transcriptome of the stem base using anatomical techniques, ultra-high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS), and RNA sequencing (RNA-seq), and compared it with stems and roots. The anatomical structure shows that the ratio of xylem to phloem changes at the base of the stem. A total of 801 compounds involved in 91 metabolic pathways were identified from the broadly targeted metabolome. Transcriptome analysis revealed 4974 differentially expressed genes (DEGs) at the stem base compared to the stem, and 5503 DEGs compared to the root. Comprehensive analyses of differentially accumulated compounds (DACs) and DEGs, in the stem base vs. stem, identified 10 valuable pathways, including plant hormone signal transduction, zeatin biosynthesis, α-Linolenic acid metabolism, histidine metabolism, carbon metabolism, carbon fixation in photosynthetic organisms, pentose phosphate pathway, galactose metabolism, and fructose and mannose metabolism. The pathways of plant hormone signal transduction and carbon metabolism were also identified by comparing the stem base with the roots. Taken together, the stem base of alfalfa is the transition region between the stem and root in morphology; in terms of material metabolism, its growth, development, and function are regulated through hormones and sugars.

Seed germination and seedling growth response of Leymus chinensis to the allelopathic influence of grassland plants.

Allelopathy has a profound impact on the germination and growth of plants, influencing the establishment of plant populations and shaping community ecological patterns. However, the allelopathic potential of many grassland species remains poorly understood. In this study, we prepared aqueous extracts from 17 herbaceous plants to investigate their allelopathic effects on the seed germination and seedling growth of Leymus chinensis, a dominant grassland species. Our results revealed that the response of L. chinensis to allelopathic compounds was dependent on the specific plant species, extract concentration, and target plant organ. Notably, Fabaceae plants exhibited a stronger allelopathic potential than Poaceae, Asteraceae, and other plant families. Moreover, we observed that root growth of L. chinensis was more sensitive to allelopathy than shoot growth, and seed germination was more affected than seedling growth. Generally, the germination of L. chinensis was strongly inhibited as the donor plant extract concentration increased. The leachate of Fabaceae plants inhibited the seedling growth of L. chinensis at concentrations ranging from 0.025 to 0.1 g mL-1. On the other hand, the leachate from other families' plants exhibited either inhibitory or hormetic effects on the early growth of L. chinensis, promoting growth at 0.025 g mL-1 and hindering it at concentrations between 0.05 and 0.1 g mL-1. These findings highlight the significant allelopathic potential of grassland plants, which plays a critical role in establishing plant populations and associated ecological processes. In addition, they shed light on the coexistence of other plants with dominant plants in the community.

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

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.