| The Inner Mongolian steppe,which comprised 74%of the region’s total area,experienced a degradation phenomenon in over 50%of the territory due to factors such as overgrazing and climate change.Leymus chinensis（Trin.）Tzvel,a Gramineae forage grass widely distributed across these steppe,primarily propagated asexually via its underground horizontal stem-the rhizome.The rhizomes of Leymus chinensis could penetrate the soil,forming a dense,net-like structure,playing a vital role in soil and water conservation,restoration of degraded grassland patches,and enhancement of productivity.However,research on the rhizomes of Leymus chinensis remained insufficiently reported.To elucidate the developmental mechanism and influencing factors of Leymus chinensis rhizomes,this study focused on the Leymus chinensis rhizomes,employing a combination of phenotypic,growth data,and multi-omics methods for investigation.The research delved into three aspects:the growth and development mechanism of Leymus chinensis rhizomes,differences in lipid components,and mineral elements,aiming to provide theoretical and technical support for the ecological restoration of the Inner Mongolian steppe.The following were the main findings and conclusions of this study:（1）Significant growth variations were evident among the sixty samples of Leymus chinensis rhizomes from the Inner Mongolian steppe.The robust rhizome fescue was widely distributed,while the weaker ones were primarily concentrated in the central region.This study established a uniform sand cultivation system in a custom-built growth chamber,facilitating the assessment of the rhizome characteristics of the sixty fescue samples.Fescue with a higher quantity of rhizomes were predominantly located in eastern areas like the Hulun Buir steppe,while those with fewer rhizomes were represented in central territories such as the Abag Banner.Fescue that produced numerous rhizome seedlings were widespread,whereas those producing fewer were chiefly found in the central region of the Xilingol League.The capacity for tillering was also widely present,while the weaker capacity was observed in the central-eastern regions of the Inner Mongolian steppe.The length of the primary rhizome and the internodal distance also followed this pattern:longer lengths and larger internodal distances were common in eastern regions such as Hulun Buir,while shorter lengths and smaller internodal distances were more frequent in central locations like Xilingol and Abag Banner.Ultimately,five strains of fescue with superior comprehensive rhizome growth capabilities（2,54,64,74,73）and five with lower capabilities（16,19,14,34,68）were selected,representing different ecological types of Leymus chinensis.（2）Rhizome-74,distinguished by its superior rhizome development capabilities,outperformed in aspects such as the quantity of rhizomes,total rhizome length,primary rhizome length,and the number of rhizome seedlings,in contrast to the underperformance of Rhizome-16.The elongation of the rhizome positively correlated with the quantity of internodes within the rhizome,influencing the biomass of the steppe grass.Compared to Rhizome-16,Rhizome-74 exhibited a higher hardness at the rhizome tip,a greater abundance of transcripts involved in cell wall component synthesis,and metabolites,including L-phenylalanine,trans-cinnamic acid,3-coumaric acid,ferulic acid,and coniferin.These metabolites,precursors of lignin,played a pivotal role in the phenylpropane biosynthesis pathway.Additionally,Rhizome-74 contained a higher quantity of growth hormone metabolites,including tryptophan（Trp）,indole-3-acetone（IPA）,indole-3-butyric acid（IBA）,indole-3-acetic acid（IAA）,and indole-3-acetyl-glucose（IAA-Glc）.The genes for auxin biosynthesis（YUCCAs）,auxin efflux carrier protein（PIN）,uridine diphosphate glycosyltransferase（UGT）,and transcriptional repressor（Aux/IAA）were upregulated.（3）This study marked the first instance of identifying distinct internal structures within the protoplasts of the Leymus chinensis rhizome,which possessed unique mitochondria.The primary lipids within the rhizome of Leymus chinensis encompassed four major categories:Glycerophospholipids（GP）,Sphingolipids（SP）,Glycerol Ester（GL）,and Fatty Acids（FA）.In comparison to the root and stem,the content of Diacylglycerols（DAG）,Triacylglycerols（TAG）,Ceramides（Cer）,and Sphingomyelins（SM）in the rhizome significantly decreased,while the levels of Fatty Acids（FA）and Phosphatidylserine（PS）notably increased.The differences between the rhizome and the stem and root were evident in the following:the rhizome was rich in ribosome and fatty acid metabolism genes,the stem abounded in starch and sucrose,galactose genes,and the root was replete with genes related to plant-pathogen interaction and oxidative stress response.（4）The optimal concentration of mineral elements was requisite for the growth and development of the rhizome of the steppe grass.Both low and high levels of calcium,as well as high zinc and low iron,inhibited the growth of the steppe grass rhizome,while magnesium did not have any significant effect.Low calcium,by reducing the quantity of rhizomes and the content of pectin,led to a thinning of the cell wall and a blunting of the rhizome tip,thereby stunting the growth of the steppe grass rhizome.Although the calcium content in the rhizomes and rhizome seedlings of steppe grass treated with low calcium declined,there was no significant difference in the calcium content between the mother plant and the tiller seedlings.The gene expression of calcium-dependent protein kinases（CDPK）was upregulated,while that of calmodulin（Ca M）was downregulated.Genes encoding auxin input protein（Aux/IAA）,pectin synthase-galacturonic acid transferase（GAUT）,and genes associated with fatty acid synthesis-long-chain acyl-coenzyme A synthase（ACSL）were downregulated.High calcium,by reducing length and quantity,increased the curvature of the rhizome,as well as the thickness of the cell wall and the content of cellulose and pectin,thus inhibiting the growth of the steppe grass rhizome.After high calcium treatment,the overall calcium content of the steppe grass increased.The gene expression of calcium-binding proteins,calcium-dependent protein kinases（CDPK）,calmodulin（Ca M）,and genes encoding calcium efflux Ca2+-ATPase were upregulated.Genes encoding auxin output protein（PIN）,pectin-degrading enzyme-polygalacturonic acid enzyme（PG）,and genes responsible for fatty acid extension-ketoacyl-coenzyme A thiolase（KCS）were downregulated.In summary,the growth and development of the rhizomes in Leymus chinensis are closely related to auxins,membrane lipid components,and mineral elements.These three factors can independently or synergistically regulate the growth of the rhizomes.This study provides a theoretical basis for perennial rhizomatous plant research and has significant implications for the restoration of the Inner Mongolia steppe. |
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