Submergence stress is a prevalent abiotic stress affecting plant growth and development and can restrict plant cultivation in areas prone to flooding. Research on plant submergence stress tolerance has been essential in managing plant production under excessive rainfall. Red clover (Trifolium pratense L.), a high-quality legume forage, exhibits low tolerance to submergence, and long-term submergence can lead to root rot and death. This study assessed the microstructure, physiological indicators, and the key genes and metabolic pathways under submergence stress in the root system of red clover HL(Hong Long) and ZY(Zi You) varieties under submergence stress at 0 h, 8 h, 24 h, 3 d, and 5 d. Based on 7740 transcripts identified in the leaves at 0 h, 8 h, and 24 h submergence stress, Weighted Gene Co-expression Network Analysis (WGCNA) was performed on the differentially expressed genes (DEGs) at 8 h and 24 h. Functional annotation of the DEGs in the four key modules was obtained. Based on the results, the red clover root system exhibited epidermal cell rupture, enlargement and rupture of cortical thin-walled cells, thickening of the mid-column, and a significant increase in the number of air cavities and air cavity area of aeration tissue with the prolongation of submergence stress. The malondialdehyde content, relative conductivity, peroxidase, and superoxide dismutase initially increased and decreased as submergence stress duration increased. Four specific modules (cyan, purple, light cyan, and ivory) closely correlated with each stress were identified by WGCNA. The 14 obtained Hub genes were functionally annotated, among which six genes, including gene51878, gene11315, and gene11848, were involved in glyoxylate and dicarboxylic acid metabolism, carbon fixation in photosynthetic organisms, carbon metabolism, biosynthesis of pantothenic acid and CoA, flavonoid biosynthesis. In this study, using WGCNA, the molecular response mechanisms of red clover to submergence stress was proposed, and the core genes and metabolic pathways in response to submergence stress were obtained, providing a valuable data resource at the physiological and molecular levels for subsequent studies of submergence stress tolerance in plants.

Introduction: The severity of flood disasters is increasing due to climate change, resulting in a significant reduction in the yield and quality of forage crops worldwide. This poses a serious threat to the development of agriculture and livestock. Hemarthria compressa is an important high-quality forage grass in southern China. In recent years, frequent flooding has caused varying degrees of impacts on H. compressa and their ecological environment.Methods: In this study, we evaluated differences in flooding tolerance between the root systems of the experimental materials GY (Guang Yi, flood-tolerant) and N1291 (N201801291, flood-sensitive). We measured their morphological indexes after 7 d, 14 d, and 21 d of submergence stress and sequenced their transcriptomes at 8 h and 24 h, with 0 h as the control.Results: During submergence stress, the number of adventitious roots and root length of both GY and N1291 tended to increase, but the overall growth of GY was significantly higher than that of N1291. RNA-seq analysis revealed that 6046 and 7493 DEGs were identified in GY-8h and GY-24h, respectively, and 9198 and 4236 DEGs in N1291-8h and N1291-24h, respectively, compared with the control. The GO and KEGG enrichment analysis results indicated the GO terms mainly enriched among the DEGs were oxidation-reduction process, obsolete peroxidase reaction, and other antioxidant-related terms. The KEGG pathways that were most significantly enriched were phenylpropanoid biosynthesis, plant hormone signal transduction etc. The genes of transcription factor families, such as C2H2, bHLH and bZIP, were highly expressed in the H. compressa after submergence, which might be closely related to the submergence adaptive response mechanisms of H. compressa.Discussion: This study provides basic data for analyzing the molecular and morphological mechanisms of H. compressa in response to submergence stress, and also provides theoretical support for the subsequent improvement of submergence tolerance traits of H. compressa.

Hemarthria compressa is a high-quality forage resource in China. In recent years, waterlogging has frequently occurred, adversely affecting the growth and development of H. compressa. In order to investigate the physiological and molecular response mechanisms of H. compressa under waterlogging stress and identify hub genes involved in waterlogging tolerance, H. compressa roots from the GY (waterlogging-tolerant) and N1291 (waterlogging-sensitive) cultivars were selected as experimental materials in this study. The physiological indexes of H. compressa were measured, and transcriptome sequencing was carried out after 8 h and 24 h of waterlogging stress, with 0 h used as the control group. Superoxide dismutase (SOD) and peroxidase (POD) activities were significantly increased in both GY and N1291 under waterlogging stress (P < 0.05). Weighted gene co-expression network analysis (WGCNA) identified a total of four modules significantly associated with waterlogging stress (r>|0.9|, P < 0.05). Gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) enrichment results showed that differentially expressed genes (DEGs) were mainly enriched in the Starch and sucrose metabolism, Plant hormone signal transduction, Ribosome and Glutathione metabolism pathways. Seven hub genes were also retrieved, including Cluster-38255.67514 and Cluster-38255.80127, potentially associated with waterlogging tolerance. It is related to the Ribosome pathway and participates in the process of anti-waterlogging regulation. The results of this experiment provide new insights into the response mechanisms of H. compressa to waterlogging stress and a theoretical framework for the effective selection and breeding of waterlogging-tolerant cultivars.

Changes of permafrost and the active layer affect geophysical process, water circulation, biological diversity and carbon storage. The monitoring of ground surface deformations is crucial and necessary to estimate the degradation of permafrost environment. In this study, the ground motions of the Tanggula section in the Qinghai- Tibet Plateau (QTP), a region with limited in situ measurements at spatial scale, have been investigated by the small baseline SAR interferometry (SBAS-InSAR). In total, 17 C-band ENVISAT ASAR images (acquired from January 1, 2009 to August 19, 2010) were employed. The results show that the ground surface motion was primarily in the range of – 7.6 mm per year to 6.7 mm per year, and the correlation coefficients and the P-values between deformations and Moderate Resolution Imaging Spectroradiometer (MODIS) Land Surface Temperatures (LSTs) were ranged from -0.24 to -0.47 and from 0.09 to 0.41, respectively. And the precision file of the surface displacement rates map is showed that the estimated displacement velocity is reliable. Our study has observed that the majority of ground surface (approximately 70%) was relatively stable in the study period with displacements in the range of -2 mm per year to 2 mm per year and the ground subsidence is larger than the ground heave, implying the necessity of time series deformations surveillance derived from satellites in the permafrost environment.

Sorghum-sudangrass hybrid silage has poor fermentation characteristics owing to a high moisture content. Accordingly, a 3 × 4+1 factorial design was applied to investigate the effects of adding different types and amounts of hay (corn stalk, wheat straw, and alfalfa hay at 12.5 kg t-1, 25 kg t-1, 37.5 kg t-1, and 50 kg t-1) on the nutritive value, fermentation quality, 72 h dry matter digestibility, and gas dynamics in vitro to simulate the rumen fermentation of sorghum-sudangrass hybrid silage. Separated silage of sorghum-sudangrass hybrids had a high butyric acid content and a FLIEG’s scores evaluation ranking of only “Fair.” The addition of hay significantly improved the fermentation quality of mixed silage. With respect to hay type, adding wheat straw had the best fermentation quality, alfalfa hay had the best nutritive value, in vitro dry matter digestibility (IVDMD) (662.41 g kg-1), constant fractional rate (C) (0.28 mL h-1), and the average gas production rate (AGPR) (32.70 mL h-1) content. There were no differences in the cumulative gas production at 72 h (GP72h), asymptotic gas production generated at a constant fractional rate (A), and lag time before gas production commenced (lag) among the three hay types. With respect to quantity, 25 kg t-1 hay had the best fermentation quality, 50 kg t-1 hay had the best nutritive value and highest IVDMD content (662.81 g kg-1), 37.5 kg t-1 hay had the highest C (0.28 mL h-1) and AGPR (31.48 mL h-1) contents, 25 kg t-1 hay had the highest Half time (2.20 h), and there were no significant differences in GP72h, A, and lag among the four amounts. Considering both nutritive value and fermentation quality, the best mixed silage mode was 37.5 kg t-1 wheat straw.