Abstract
To investigate photosynthetic characteristics of the subtending leaf at the 2-3rd and 10-11th fruiting branch (FBN, FB2-3, and FB10-11), and their relationship with cotton yield and quality, field experiments were conducted using two cotton cultivars, Kemian 1 and Sumian 15. The results showed that with FBN increasing, chlorophyll (Chl) components, Pn and non-photochemical quenching (NPQ) in the subtending leaf significantly declined, while soluble sugar, amino acid and their ratio (C SS/C AA) as well as F v/F m increased. These results indicated that (1) non-radiative dissipation of excess light energy at FB2-3 was reduced to improve solar energy utilization efficiency to compensate for lower Pn, (2) higher NPQ at FB10-11 played a role in leaf photo-damage avoidance, (3) boll weight was related to the C SS/C AA ratio rather than carbohydrates content alone, (4) with FBN increasing, lint biomass and lint/seed ratio increased significantly, but lint yield decreased due to lower relative amount of bolls, and (5) the decreases in Pn, sucrose content and C SS /C AA in the subtending leaf at FB2-3 resulted in lower boll weight and fiber strength.