Chromosome-level reference genome assembly provides insights into the evolution of Pennisetum alopecuroides

Pennisetum alopecuroides is an important forage grass resource, which plays a vital role in ecological environment improvement. Therefore, the acquisition of P. alopecuroides genome resources is conducive to the study of the adaptability of Pennisetum species in ecological remediation and forage breeding development. Here we assembled a P. alopecuroides cv. 'Liqiu' genome at the chromosome level with a size of approximately 845.71 Mb, contig N50 of 84.83Mb, and genome integrity of 99.13% as assessed by CEGMA. A total of 833.41-Mb sequences were mounted on nine chromosomes by Hi-C technology. In total, 60.66% of the repetitive sequences and 34,312 genes were predicted. The genomic evolution analysis showed that P. alopecuroides cv. 'Liqiu' was isolated from Setaria 7.53-13.80 million years ago and from Cenchrus 5.33-8.99 million years ago, respectively. The whole-genome event analysis showed that P. alopecuroides cv. 'Liqiu' underwent two whole-genome duplication (WGD) events in the evolution process, and the duplication events occurred at a similar time to that of Oryza sativa and Setaria viridis. The completion of the genome sequencing of P. alopecuroides cv. 'Liqiu' provides data support for mining high-quality genetic resources of P. alopecuroides and provides a theoretical basis for the origin and evolutionary characteristics of Pennisetum.

Effects of root exudates on the activation and remediation of cadmium ion in contaminated soils

To screen out plants with hyperaccumulation of heavy metals and explore the effects of root exudates on the phytoremediation in contaminated soils. The germination rates of five plants including Lolium perenne L. (L. perenne), Sorghum sudanense (Piper) Stapf. (S. sudanense), Pennisetum alopecuroides (L.) Spreng. (P. alopecuroides), Medicago sativa L. (M. sativa), and Trifolium repens L. (T. repens) in different concentrations of cadmium ion solution (0-100 mg/kg) were determined. The growth adaptability of these five plants under conditions of contaminated soils with the above cadmium ion concentrations was also evaluated. S. sudanense and P. alopecuroides had higher germination rates and better growth than the three other plants and were selected as the latter experimental varieties. The activation amounts of cadmium ion in soils were measured using AAS in the presence of three types of root secretions (citric acid, glycine, and maltose) with different concentrations (10-500 mmol/L). The activation amounts decrease in the following order: citric acid > glycine > maltose. The effect of these three root exudates on the removal of cadmium-contaminated soils in combination with S. sudanense and P. alopecuroides was also tested. For S. sudanense and P. alopecuroides, the maximum biomass and removal rate reaches the maximum at 100 mmol/L of citric acid. Conversely, low concentrations (approximately 10-50 mmol/L) of glycine and maltose are more effective for plant growth and phytoremediation. The addition of citric acid at 100 mmol/L and approximately 10-50 mmol/L of glycine and maltose can effectively promote the transfer of cadmium ion from roots to leaves and the accumulation of cadmium ion in leaves.

[Urban Runoff Phosphorus Removal Pathways in Bioretention Systems]

The role of vegetation and saturated zones in stormwater-dissolved phosphorus (PO₄^3--P) removal was investigated using bioretention microcosms. Nine bioretention columns were dosed with synthetic stormwater under various hydrological conditions and phosphorus loading rates and monitored over a 12-month period. Remarkable phosphorus removal (>90%) was achieved using the mixed filter media of sand and local soil, with or without vegetation. Bioretention columns in which P. alopecuroides was planted could significantly enhance PO₄^3--P removal. The saturated zones could also reduce the effluent PO₄^3--P concentrations, but had no significant effect on total phosphorus removal. Approximately 50% of the input phosphorus retained in the filter media was extracted in the top 0-22.5 cm, where it could be available for uptake by plants. Further, 57.1% to 76.1% of the total phosphorus input recovered in the total plant biomass was stored in the above-ground shoots. Thus, periodic harvesting of shoots can be a sustainable method of phosphorus removal from stormwater bioretention systems.