Dynamic Changes in Carbohydrate Accumulation and Activities of Associated Fructan-Metabolizing Enzymes Throughout All Growth Stages of Garlic (Allium sativum L.)

Fructan metabolism governs garlic bulb expansion and yield formation. Dynamic carbohydrates and four fructan-metabolizing enzymes (1-FFT, 1-SST, 1-FEH, INV) of ‘Ledu purple garlic’ were tracked over 0–84 days after transplanting. Combined with multivariate statistics and carbon contribution quantification, we analyzed source–sink carbohydrate allocation. Garlic growth was divided into three phases: 0–42 d leaf vegetative growth, 42–56 d synchronous leaf and bulb development, and 56–84 d rapid bulb bulking. Fructan was the dominant storage carbohydrate in bulbs, peaking at 869.81 mg·g−1 DW at harvest. Aerial carbohydrates were degraded and remobilized underground in late growth, while bulb monosaccharides showed bimodal fluctuations. Carbon supply shifted sequentially: mother bulbs supplied carbon at the seedling stage, leaves and pseudostems co-provided photosynthates in the mid-term, and pseudostems became the major temporary remobilizable carbon storage organ during late bulking under this single-site trial with a 14-day sampling interval. Fructan contents and enzyme activities exhibited obvious stage-specific patterns and could act as potential biochemical markers for distinguishing growth stages of ‘Ledu purple garlic’ under the present single-site field trial; their broad applicability across diverse garlic cultivars remains to be verified. 1-FFT was active only in early stages, while bulb 1-SST increased continuously. Day 42 represented the source–sink transition threshold with peak INV activity. Synchronous variation in enzyme activities only hints at coordinated carbohydrate redistribution under this test environment, which may support bulb dry matter accumulation.