Slight Shading Stress at Seedling Stage Does not Reduce Lignin Biosynthesis or Affect Lodging Resistance of Soybean Stems

Effects of nitrogen fertilizer application rate on lodging resistance for rice (Oryza sativa L.) stem

Rice yield could be increased by apply higher level of nitrogen fertilizer, but excessive use of nitrogen fertilizer will cause plant lodging. This study aimed to investigate the effect of nitrogen application rate on lodging resistance of rice stems. Four japonica rice varieties with different lodging resistance were used, and six nitrogen fertilizer levels were set up to analyze the morphological structure, mechanical properties, and chemical components of rice stems under such treatments. The dynamic changes of lodging resistance of rice stems under different nitrogen fertilizer application rates were exanimated. The study provide valuable insights for improving lodging resistance and subsequently increasing rice yield. The results indicated that WYD4 exhibited the highest yield under the N1 treatment, whereas JYJ, JJ 525, and JND 667 achieved the highest yield under the N2 treatment. The lodging index of rice varieties fluctuated at the filling stage, peaking 30 days after heading. Moreover, the lodging index increased progressively with higher nitrogen fertilizer application rates, reaching its maximum under the N5 treatment, which corresponded to an increased lodging risk. Specifically, the lodging index under the N5 treatment increased by 0.63-1.21 times compared to the optimal nitrogen fertilizer level. Concurrently, the fracture bending point (s) and lodging resistance of the rice stem exhibited a gradual decline. Additionally, plant height, internode length, and barycenter height significantly increased with rising nitrogen application rates and were positively correlated with the lodging index. Conversely, the wall thickness of the second basal node decreased and showed a negative correlation with the lodging index. Furthermore, the contents of lignin, cellulose, soluble sugar, and starch in the second internode diminished with increasing nitrogen rates, and were positively correlated with the breaking moment.

Optimum nitrogen improved stem breaking resistance of intercropped soybean by modifying the stem anatomical structure and lignin metabolism

Excessive use of nitrogen fertilizers enhanced the stem lodging, leading to serious threats to environmental sustainability. As the maize-soybean intercropping system is eco-friendly, however, soybean micro-climate hinders soybean growth and caused lodging. Since the relationship between nitrogen and lodging resistance under the intercropping system is not widely studied. Therefore, a pot experiment was conducted with the application of different nitrogen concentrations referring to low nitrogen (LN) = 0 mg/kg, optimum nitrogen (OpN) = 100 mg/kg, and high nitrogen (HN) = 300 mg/kg. To evaluate the optimum nitrogen fertilization under the maize-soybean intercropping system, two soybean cultivars were selected Tianlong 1 (TL-1), (lodging resistant) and Chuandou 16 (CD-16), (lodging susceptible). The results revealed that under the intercropping system, the OpN concentration significantly improved the lodging resistance of soybean cultivars by reducing the plant height of TL-1 and CD-16 by 4 and 28% as compared to LN, respectively. Following OpN, the lodging resistance index for CD-16 was also increased by 67% and 59% under the respective cropping systems. In addition, we found that OpN concentration prompted the lignin biosynthesis by stimulating the enzymatic activities of lignin biosynthetic enzymes (PAL, 4CL, CAD, and POD), which was reflected at the transcriptional levels (GmPAL, GmPOD, GmCAD, Gm4CL), too. Henceforth, we proposed that optimum nitrogen fertilization boosts soybean stem lodging resistance by modulating the lignin metabolism in the maize-soybean intercropping system.

A Joint Transcriptomic and Metabolomic Analysis Reveals the Regulation of Shading on Lignin Biosynthesis in Asparagus

Asparagus belongs to the Liliaceae family and has important economic and pharmacological value. Lignin plays a crucial role in cell wall structural integrity, stem strength, water transport, mechanical support and plant resistance to pathogens. In this study, various biological methods were used to study the mechanism of shading on the asparagus lignin accumulation pathway. The physiological results showed that shading significantly reduced stem diameter and cell wall lignin content. Microstructure observation showed that shading reduced the number of vascular bundles and xylem area, resulting in decreased lignin content, and thus reducing the lignification of asparagus. Cinnamic acid, caffeic acid, ferulic acid and sinapyl alcohol are crucial intermediate metabolites in the process of lignin synthesis. Metabolomic profiling showed that shading significantly reduced the contents of cinnamic acid, caffeic acid, ferulic acid and sinapyl alcohol. Transcriptome profiling identified 37 differentially expressed genes related to lignin, including PAL, C4H, 4CL, CAD, CCR, POD, CCoAOMT, and F5H related enzyme activity regulation genes. The expression levels of POD, CCoAOMT, and CCR genes were significantly decreased under shading treatment, while the expression levels of CAD and F5H genes exhibited no significant difference with increased shading. The downregulation of POD, CCoAOMT genes and the decrease in CCR gene expression levels inhibited the activities of the corresponding enzymes under shading treatment, resulting in decreased downstream content of caffeic acid, ferulic acid, sinaperol, chlorogenic acid and coniferin. A significant decrease in upstream cinnamic acid content was observed with shading, which also led to decreased downstream metabolites and reduced asparagus lignin content. In this study, transcriptomic and metabolomic analysis revealed the key regulatory genes and metabolites of asparagus lignin under shading treatment. This study provides a reference for further understanding the mechanism of lignin biosynthesis and the interaction of related genes.

Foliar Application of NH4 +/NO3 - Ratios Enhance the Lodging Resistance of Soybean Stem by Regulating the Physiological and Biochemical Mechanisms Under Shade Conditions

Shading is one of the most chronic restrains which can lead to the lodging of intercropped plants. In order to increase the soybean stem lodging resistance, a 2-year field trial was conducted to evaluate the impact of different ratios and concentrations of NH₄ ⁺/NO₃ ^- on the morpho-physiological and biochemical characteristics of soybean stem under shade conditions. The total 5 ratios of NH₄ ⁺/NO₃ ^- were applied as follows: T0 = 0/0 (control), T1 = 0/100 (higher ratio), T2 = 25/75 (optimum), T3 = 50/50 (optimum), and T4 = 75/25 (higher ratio) as a nitrogen source. Our findings displayed that the T2 (25/75) and T3 (50/50) treatments alleviated the shading stress by improving the photosynthetic activity, biomass accumulation, carbohydrates contents, and lignin related enzymes (POD, CAD, and 4Cl) which led to improvement in stem lodging resistance. The correlation analysis (p ≤ 0.05, p ≤ 0.01) revealed the strong relationship between lodging resistance index and stem diameter, stem strength, lignin content, photosynthesis, and lignin related enzymes (POD, CAD, and 4CL) evidencing the strong contribution of lignin and its related enzymes in the improvement of lodging resistance of soybean stem under shade conditions. Collectively, we concluded that optimum NH₄ ⁺/NO₃ ^- ratios (T2 and T3) can boost up the lodging resistance of soybean stem under shade stress.

Enhancement of Lodging Resistance and Lignin Content by Application of Organic Carbon and Silicon Fertilization in Brassica napus L

This study was aimed to investigate the effects of organic carbon and silicon fertilizers on the lodging resistance, yield, and economic performance of rapeseed. Two cultivars, namely Jayou (lodging-resistant) and Chuannongyou (lodging-susceptible), were selected to evaluate the effects of various fertilizer treatments on rapeseed culm morphology, lignin accumulation, and their relationships with their lodging resistance indices. The results showed that both organic carbon and silicon fertilizer applications increased the plant height, basal stem diameter, internode plumpness, and bending strength of rapeseed in both the studied years. The bending strength was significantly and positively correlated with the lodging resistance index and lignin content. It was found that both organic carbon and silicon fertilizers had improved the activities of lignin biosynthesis enzymes (phenylalanine ammonia-lyase, 4-coumarate:CoA ligase, cinnamyl alcohol dehydrogenase, and peroxiredoxins) and their related genes to increase lignin accumulation in the culm, which ultimately improved the lodging resistance. At the same time, the thickness of the stem cortex, vascular bundle area, and xylem area was increased, and the stem strength was improved. The effect of silicon fertilizer was better than that of organic carbon fertilizer, but there was no significant difference with the mixed application of silicon fertilizer and organic carbon fertilizer. Similarly, silicon fertilizer increased the number of pods, significantly increased the yield, and improved the economic benefit, while organic carbon fertilizer had no significant effect on the yield. Therefore, we believe that organic carbon and silicon fertilizer can improve the lodging resistance of rape stems by improving the lignin accumulation and the mechanical tissue structure. Still, the effect of silicon fertilizer is the best. Considering the economic benefits, adding silicon fertilizer can obtain more net income than the mixed application of silicon fertilizer and organic carbon fertilizer.

Foliar application of silicon improves growth of soybean by enhancing carbon metabolism under shading conditions

An experiment was set up to investigate physiological responses of soybeans to silicon (Si) under normal light and shade conditions. Two soybean varieties, Nandou 12 (shade resistant), and Nan 032-4 (shade susceptible), were tested. Our results revealed that under shading, the net assimilation rate and the plant growth were significantly reduced. However, foliar application of Si under normal light and shading significantly improved the net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and decreased intercellular carbon dioxide concentration (Ci). The net photosynthetic rate of Nandou 12 under normal light and shading increased by 46.4% and 33.3% respectively with Si treatment (200 mg/kg) compared to controls. Si application also enhanced chlorophyll content, soluble sugars, fresh weight, root length, root surface area, root volume, root-shoot ratio, and root dry weight under both conditions. Si application significantly increased the accumulation of some carbohydrates such as soluble sugar and sucrose in stems and leaves ensuring better stem strength under both conditions. Si application significantly increased the yield by increasing the number of effective pods per plant, the number of beans per plant and the weight of beans per plant. After Si treatment, the yield increased 24.5% under mono-cropping, and 17.41% under intercropping. Thus, Si is very effective in alleviating the stress effects of shading in intercropped soybeans by increasing the photosynthetic efficiency and lodging resistance.

Foliar application of silicon improves stem strength under low light stress by regulating lignin biosynthesis genes in soybean (Glycine max (L.) Merr.)

In order to improve soybean's resistance to lodging, silicon (Si) solutions at concentrations of 0,100, 200,300 mg kg-1 were applied during the seedling stage. The Si accumulation in different parts of the plants, the photosynthetic parameters of leaves and chlorophyll content, the stem bending resistance, the expression of genes of lignin biosynthesis and associated enzyme activity and sap flow rates were measured at early and late growth stages. The potential mechanisms for how Si improve growth and shade tolerance, enhances lodging resistance and improves photosynthesis were analyzed to provide a theoretical basis for the use of Si amendments in agriculture. After application of Si at 200 mg kg-1, the net photosynthetic rate of soybeans increased by 46.4 % in the light and 33.3 % under shade. The application of Si increased chlorophyll content, and fresh weight of leaves, reduced leaf area and enhanced photosynthesis by increasing stomatal conductance. The activity of peroxidase (POD), 4-coumarate:CoA ligase (4CL), cinnamyl alcohol dehydrogenase (CAD) and phenylalanine ammonia-lyase (PAL) increased during pre-and post-growth periods, whereas Si also increased lignin accumulation and inhibited lodging. We concluded that Si affects the composition of plant cell walls components, mostly by altering linkages of non-cellulosic polymers and lignin. The modifications of the cell wall network through Si application could be a useful strategy to reduce shading stress in intercropping.

Agro-Techniques for Lodging Stress Management in Maize-Soybean Intercropping System-A Review

Lodging is one of the most chronic restraints of the maize-soybean intercropping system, which causes a serious threat to agriculture development and sustainability. In the maize-soybean intercropping system, shade is a major causative agent that is triggered by the higher stem length of a maize plant. Many morphological and anatomical characteristics are involved in the lodging phenomenon, along with the chemical configuration of the stem. Due to maize shading, soybean stem evolves the shade avoidance response and resulting in the stem elongation that leads to severe lodging stress. However, the major agro-techniques that are required to explore the lodging stress in the maize-soybean intercropping system for sustainable agriculture have not been precisely elucidated yet. Therefore, the present review is tempted to compare the conceptual insights with preceding published researches and proposed the important techniques which could be applied to overcome the devastating effects of lodging. We further explored that, lodging stress management is dependent on multiple approaches such as agronomical, chemical and genetics which could be helpful to reduce the lodging threats in the maize-soybean intercropping system. Nonetheless, many queries needed to explicate the complex phenomenon of lodging. Henceforth, the agronomists, physiologists, molecular actors and breeders require further exploration to fix this challenging problem.