Seasonal dynamics of morphology, carbon, and nitrogen reserves in two bermudagrass accessions ( Cynodon dactylon (L.)) differing in tolerance to long‑term low nitrogen supply

Understanding how wild bermudagrass (Cynodon dactylon (L.) Pers.) maintains its persistence in nutrient-poor habitats through seasonal nitrogen cycling is of important for reducing nitrogen inputs. The seasonal dynamics of growth and nitrogenous and carbohydrate compounds were determined in two wild bermudagrass germplasms (C291, low-N-tolerant, C134, low-N-sensitive) under low N (0.5 mM) and control N (5 mM) levels. The results revealed that the rhizome accounted for the highest proportion of the plant dry weight, stored nutrients and contained buds, and played a crucial role in determining the perenniality of bermudagrass. In winter, free amino acids and starch stored in the rhizome served as the primary sources for nitrogen and carbon, respectively, which were subsequently remobilized, along with soluble sugars, to support spring regrowth in the following year. In addition, a low N supply decreased the free amino acid content but increased the ratio of soluble sugars to free amino acids in wild bermudagrass. For the two accessions, C291 was more tolerant to long-term low-N treatment than C134, with the rhizome bud density decreasing less than that of C134 because the internode length of C291 decreased compared with control. Moreover, a greater proportion of free amino acids was stored in the rhizomes of C291, and some of the starch stored in the rhizomes of C291 was remobilized for regrowth at the spring green-up stage. These findings highlight rhizome bud viability, reserve remobilization, and compact architecture as key targets for breeding low-N-tolerant bermudagrass, as exemplified by C291 superior bud retention and reserve utilization under low N.