Leaf expansion and development of PHOTOSYNTHETIC CAPACITY AND PIGMENTS IN Liquidambar styraciflua (Hamamelidaceae)—EFFECTS OF UV‐B RADIATION

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In order to perform their functions as photosynthetic organs, leaves must cope with excess heat and potentially damaging ultraviolet radiation. Possible increases in the UV‐B portion of the solar spectrum may place an additional burden on leaves, and this could be particularly important for young expanding leaves with poorly developed UV‐B defense mechanisms. We evaluated the effects of supplemental UV‐B radiation on leaf expansion and the development of photosynthetic capacity and pigments in sweetgum (Liquidambar styraciflua L.) seedlings. Seedlings were grown in the field under either ambient or ambient plus 3 or 5.0 kJ of biologically effective supplemental UV‐B radiation. Although final leaf size was unaffected, the rate of leaf elongation and accumulation of leaf area was slower in leaves exposed to the lower supplemental UV‐B irradiance. In contrast, chlorophyll accumulation and the development of photosynthetic capacity was more rapid in plants exposed to the higher, compared to the lower supplemental UV‐B irradiance. The accumulation of anthocyanins and other putative flavonoids or UV‐absorbing compounds was scarcely affected by exposure to supplemental UV‐B radiation. These results suggest that the UV‐B portion of the solar spectrum may, in the absence of gross affects on biomass, exert subtle influences on leaf ontogeny and the development of photosynthetic pigments and capacity in sweetgum.