Abstract: Light heterogeneity leads to anatomically and physiologically heterogeneous features in leaves.  However, little attention has been paid to the effects of nonuniform illumination on the anatomical and photosynthetic performance on both sides along the leaf main vein.  This study explored such effects by combining in situ determination in the field with shading simulation in the phytotron, on pima cotton that has cupping leaves.  Photosynthetic characteristics and morphological structures were measured in the field on both sides along the main vein of eastward, westward, southward, and northward leaves.  The results showed that the difference in photosynthetic capacity between the two sides along the main vein in different directions was closely related to the daily photo irridiance (DPI).  This result indicates that the photosynthetic heterogeneity between the two sides is related to their intercepted light energy.  The conclusion was further verified by the shading simulation experiments.  Photosynthetic capacity and leaf thickness of the unshaded sides of leaves in the half-shaded treatment decreased, compared to those in the unshaded treatment.  Therefore, it is conjectured that the development of  photosynthetic characteristics on one side is systematically regulated by that on the other side.  The study provides theoretical guidance on accessing the feasibility of sampling and directional planting.   

Key words: photosynthetic heterogeneity , morphological traits ,  leaf mass per area ,  shade ,  systemic regulation