Photosynthesis diversity of Isodon rubescens (Hemsley) H. Hara leaves at different leaf positions.

There are 5-15 pairs of leaves on the stem of Isodon rubescens. The I. rubescens leaves at different nodes are far apart because the internodes are long. The photosynthetic rates, light response curves and chlorophyll fluorescence characteristics of I. rubescens leaves at different leaf positions were determined in this study to clarify the differences in photosynthetic capacity distinctions of among these leaves. The results showed that the photosynthetic capacity of I. rubescens leaves on the upper part of the stem was slightly lower than that of the leaves on the middle part of the stem. However, the incompletely unfolded tender leaf on the upper part of the I. rubescens stem possessed considerable photosynthetic capacity. The leaves on the middle part of the I. rubescens stem were the main site of photosynthesis for the plant. The I. rubescens leaves at the lower leaf position exhibited a lower photosynthetic capacity. Pruning during the cultivation and management of I. rubescens could prompt the formation of tender leaves and therefore increase the photosynthetic efficiency of plants.