Seasonal dynamics and effect of harvest time on the concentration and yield of non-structural carbohydrates in rhizomes and aboveground biomass of giant reed (Arundo donax L.)

Non-Structural Carbohydrates (NSC) in giant reed (Arundo donax L.), a perennial energy grass characterized by high carbon accumulation rates, remain poorly studied. The objective of this study is to investigate how harvest timing under varying seasonal conditions influences the concentration and yield of NSC in different giant reed organs, including belowground reserves essential for plant regrowth. In a two-year field study, biomass from leaves, culms and rhizomes was collected at eight sampling times from spring to winter, and NSC (i.e. starch, water-soluble carbohydrates) were quantified. Results revealed organ‐specific patterns: in leaves, hexoses were generally prevalent, starch was dominant over sucrose during early growth; in culms, starch prevailed during senescence, sucrose prevailed at earlier stages; in rhizomes, sucrose was generally more abundant than starch, averaging 178 vs 69 mg g−1 DM. However, sprouting relied on rhizome starch, which peaked in late summer, rather than sucrose; sucrose was used later in the season and then restored. Relevant amounts of NSC were found in aboveground biomass harvested in summer, peaking in late August (up to 3.2 t ha−1), then partly retained until wintertime (1.1–1.8 t ha−1), though differences between years emerged, especially in leaf sucrose and total NSC in culms. Belowground reserves showed differences between sampling times but not between years. These findings suggest that harvesting in late summer can enhance the NSC content of biomass while preserving belowground carbohydrate reserves.