Strong increase of photosynthetic pigments and leaf size in a pruned Ginkgo biloba tree

Abstract

A 50-year-old solitary, sun-exposed ginkgo tree had strongly been pruned in the fall of 2021. Very few buds for the formation of new leaves, twigs, and branches were left over. In spring 2022, these few remaining buds responded with the formation of a different leaf type. These leaves were 2.7 times larger and also thicker than in the years before. In addition, the mean content of total chlorophylls [Chl (a+b)] per leaf area unit of dark-green leaves was 1.45, those of green leaves two times higher as compared to the years before pruning and the two other ginkgo trees which had been investigated in parallel. A comparable increase was also found for the level of total carotenoids (x+c). The mean content for Chl (a+b) were 1,118 mg m^-2 for dark-green and 898 mg m^-2 for green leaves as compared to 435 to 770 mg m^-2 in leaves of other trees. The higher values for Chl (a+b) and total carotenoid content showed up also on a fresh and dry mass basis. Thus, with the formation of a new, larger leaf type by changes in morphology (leaf size and thickness) and the increase of photosynthetic pigments, the pruned ginkgo tree was able to compensate for the much lower number of leaves and photosynthetic units.

Keywords: chlorophyll a/b ratio; chlorophyll levels; leaf size; leaf thickness; ratio of chlorophylls to carotenoids; total carotenoid content.

Fig. 1. Dark-green leaves of a male ginkgo tree (tree 1) in summer 2022 which had very strongly been recut and pruned in the fall of 2021. One very large dark-green leaf was formed as first in spring 2022 at each of the few buds on thin stems. These leaves had an unusual large leaf size of 128 cm² (left) and 91 cm² (right). The three smaller light-green leaves shown were formed in June at the end of newly formed branches (shoots) of the same tree. (The razor blade shown serves as a measure, it has a length of 2 cm.)

Fig. 2. Dark-green relatively large ginkgo leaves in summer 2022 being formed in the spring on the buds of one of the few left-over branches of the strongly pruned male ginkgo tree (tree 1). (The razor blade shown serves as scale, it has a length of 2 cm.)

Fig. 3. Dark-green normal size ginkgo leaves in August 2022 from an old female tree at the KIT campus (tree 2). The largest leaf (down right) had only a leaf area of 46 cm². (The razor blade shown serves as scale, it has a length of 2 cm.)

Fig. 4. Green normal-size sun leaves in August 2022 from a younger male ginkgo tree (tree 3). (The razor blade shown serves as scale, it has a length of 2 cm.)

Fig. 5. Leaf-area size distribution of 100 leaves each of two ginkgo trees (tree 2 and 3). The points shown indicate the number of leaves in the range of 5–10, 10–15, and 15–20 cm², etc., up to 40–45 cm².

Fig. 6. Leaf-area size distribution of 100 leaves of ginkgo tree 1 which had very strongly been pruned in the fall of 2021 and showed in 2022 extra-large leaves. The points shown represent the number of leaves in the range of 10–20, 20–30, 30–40 and 40–50 cm², etc.