Photosynthetic characteristics of the subtending leaf of cotton boll at different fruiting branch nodes and their relationships with lint yield and fiber quality

To investigate photosynthetic characteristics of the subtending leaf at the 2–3rd and 10–11th fruiting branch (FBN, FB(2–3), and FB(10–11)), 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 FB(2–3) was reduced to improve solar energy utilization efficiency to compensate for lower Pn, (2) higher NPQ at FB(10−11) 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 FB(2–3) resulted in lower boll weight and fiber strength.