The role of cotyledons in growth and development of woody angiosperms

Abstract

The role of photosynthetically active cotyledons in the growth of young woody angiosperm seedlings was studied over a 35-day period under controlled environmental conditions. Two experiments were performed. In the first, cotyledons of Robinia pseudoacacia, Ulmus americana, and Ailanthus altissima were removed or covered at 7, 14, or 21 days after seedling emergence. In the second experiment, seedlings of Robinia pseudoacacia, Betula alleghaniensis, and Acer saccharum were grown over a range of light intensities. Removing or covering Robinia cotyledons of seedlings of any age resulted in lower dry weights of roots and stems than in controls. Removing or covering cotyledons of only 7-day-old Robinia seedlings retarded dry weight increase of foliage. Robinia seedling heights were unaffected by cotyledon covering or removal. Covering Ulmus americana cotyledons had no significant effect on dry weight increment of stems or foliage or on seedling height. Removal of Ulmus cotyledons from 7-day-old seedlings inhibited dry weight increase of roots, stems, and leaves and inhibited height growth. Removal of Ailanthus cotyledons inhibited dry weight increment of roots, stems, and leaves more than did covering of cotyledons. Species varied greatly in cotyledon development and response to light intensity. Cotyledon size was affected by light intensity in Robinia, but not in Betula or Acer. Responses of cotyledons to light intensity differed from those of foliage leaves. Cotyledon photosynthesis appeared to have a very important role in seedling growth in Robinia and Ailanthus and a less important role in Ulmus.